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Activated clotting time

Also called: (ACT); Activated Coagulation Time

Specimen or type of test:

Purpose of the test

The activated clotting time is used to measure the anticoagulation effect of high-dose heparin therapy during cardiac bypass surgery with extracorporeal circulation, angioplasty, and hemodialysis. It is also used to determine the dose of protamine sulfate needed to reverse the anticoagulant effect of heparin after completion of the surgical procedure.

Basics the nurse needs to know

When the patient receives very high doses of heparin medication, frequent monitoring of the anticoagulation effect is required. If the anticoagulant effect of the heparin is insufficient, the clotting time will be lower than the therapeutic value and the patient may form a blood clot. If the anticoagulant effect of the heparin therapy is beyond the therapeutic range, the patient may develop a hemorrhage. This blood test measures the time it takes for the blood to form a clot.

When high doses of heparin are given, the therapeutic values are elevated because it takes a longer time for the blood to coagulate. This is a desirable goal because the patient is protected from formation of a thrombus or embolus during the surgery or procedure. The therapeutic values vary with the type of procedure and coagulation risk that is involved. Generally, the therapeutic goal of anticoagulation during cardiopulmonary bypass surgery is longer than 400 to 500 seconds and during cardiac angioplasty, the therapeutic value is longer than 350 seconds.

The specimen for the activated clotting time is analyzed in point-of-care testing. This means that the analyzer instrument is at the patient’s bedside or near the patient care unit so that test results can be obtained without delay. Several types of analyzer instruments are available. The test method and the test values vary with the analyzer instrument used. The nurse should refer to the instructions and normal values determined by the institution’s laboratory and the manufacturer.

REFERENCE VALUES

70 to 180 seconds

How the test is done

Venipuncture is performed to collect a sample of venous blood.

Significance of test results

Elevated values

Anticoagulation with heparin

Severe deficiency of coagulation factors of the intrinsic pathway (except Factors VII and VIII)

Interfering factors

• Contamination with heparin in the intravenous line

• Hemodilution/hemoconcentration

NURSING CARE

Nursing actions are similar to those used in other venipuncture procedures (see Chapter 2), with the following additional measures.

Pretest

• The nurse uses a flow sheet that provides for documentation of the time, amount, and route of heparin administration, as well as the time and result of ACT testing.

During the test

• If the nurse collects the specimen of blood, the intravenous line that contains heparin or heparin infusion should not be used. Select a vein in the opposite arm because the heparin in the intravenous line or catheter would falsely elevate the test result. Some specimen tubes require vigorous shaking to mix the blood with the activator in the tube. Other tubes require gentle mixing. The nurse should refer to the specific manufacturer’s instructions for reference information. Once obtained, the specimen should be placed in the analyzer, without delay.

Posttest

• Using sterile gauze, the nurse applies pressure on the venipuncture site until bleeding ceases. There is a tendency to bleed for a longer time than usual because the patient is very anticoagulated.

• The nurse frequently assesses for signs of abnormal bleeding, as into the urine or from the gingivae and mucosa in the mouth. The skin is assessed for bruising, bleeding, and petechiae.

• Each ACT test result is posted in the patient’s record and on the flow sheet.

Nursing response to critical values

When the activated clotting time result is elevated, the patient may begin to bleed or hemorrhage. The nurse performs frequent assessment for signs of bleeding and monitors the values of ACT test results.

The nurse keeps protamine sulfate on hand for use in case of hemorrhage. The action of protamine sulfate is to neutralize heparin, usually within 5 minutes after it is administered. If prescribed, this medication in its undiluted state is injected very slowly, intravenously. When protamine sulfate is administered, the nurse monitors the vital signs because if it is administered too rapidly, this medication can result in severe hypotension, bradycardia, and dyspnea. Thereafter, ACT values are monitored because of a potential heparin rebound effect that can occur several hours later. Protamine sulfate would lower the ACT value; a heparin rebound effect would again raise the ACT value.

Activated partial thromboplastin time

Also called: (APTT); Partial Thromboplastin Time (PTT)

Specimen or type of test:

Purpose of the test

This test helps identify bleeding or clotting disorders that are hereditary or acquired. It is used to monitor the effect of heparin anticoagulant therapy and to adjust the dosage of heparin based on the test results.

Basics the nurse needs to know

The activated partial thromboplastin time measures the number of seconds needed for a clot to form. The test results include the patient’s value and the control value. The control value of the test is the reference or normal value that is used to evaluate the patient’s test result. The APTT is used to monitor the results of anticoagulation therapy with heparin, hirudin, or argatroban. The goal of anticoagulation therapy is to maintain the APTT in a therapeutic range of about 1.5 to 2.5 times the normal value. For example, if the control (normal) value is 30 seconds, the anticoagulated patient’s therapeutic value should be in the range of 45 to 75 seconds. With a prolonged APTT, the patient takes longer to make a clot, and a thrombus or embolus is less likely to develop.

If the patient has an impairment of the intrinsic coagulation system that causes a prolonged APTT, the medical treatment may be a transfusion of whole blood or plasma so that the clotting factors are increased and the APTT value returns to normal.

How the test is done

Venipuncture or capillary puncture is used to obtain a sample of venous blood.

Interfering factors

• Inadequate blood sample

NURSING CARE

Nursing actions are similar to those used in other venipuncture procedures (see Chapter 2), with the following additional measures.

Pretest

• When heparin is given in intermittent doses, the time for APTT monitoring is 6 hours after the anticoagulant is given. This timing provides accurate information and allows the physician to adjust the heparin dose as needed.

• When a continuous intravenous infusion of heparin is started, the APTT is drawn every 6 hours after the initial dose of anticoagulant for the first day and 6 hours after changing the medication dosage. Once the therapeutic range of anticoagulation is achieved, the APTT is tested once a day.

Posttest

• For the patient receiving anticoagulants, assess the venipuncture site for signs of bleeding or ecchymosis. To promote clotting at the venipuncture site, the nurse uses sterile gauze to apply pressure to the site or raises the patient’s arm above the head while maintaining pressure on the site. Prolonged pressure is often needed because of the anticoagulant effect.

• When the patient receives heparin anticoagulation therapy, the nurse monitors each APTT result for a value in the therapeutic range. If the result is elevated beyond the therapeutic range, the nurse notifies the physician. The physician may lower the dose of the anticoagulant or the intravenous infusion with heparin may be discontinued for a short time. Protamine sulfate, the antidote to heparin, is kept available in case of a severe, excess anticoagulation result. When prescribed, the nurse injects the protamine sulfate subcutaneously.

• Patient teaching.

The nurse teaches the anticoagulated patient how to protect against a bleeding episode. The patient should use an electric razor for shaving and a soft toothbrush to avoid scraping of the gingiva (gums) of the oral cavity. Over-the-counter medications such as aspirin and remedies that contain aspirin are to be avoided because they interfere with platelet aggregation. The patient is taught to observe signs of abnormal bleeding in the skin, gingiva, vomitus, stool, and urine.

Nursing response to critical values

If the APTT value is in the critical value range, the physician must be notified. The patient is at risk for spontaneous bleeding or hemorrhage.

The nurse assesses the patient for spontaneous bleeding, oozing of blood, bruising, and petechiae. The nurse observes the skin, mucus membranes, and gingiva of the oral cavity, and the urine and stool for manifestations of bleeding. The vital signs are taken, observing for hypotension and tachycardia. The nurse asks the patient if he or she has a headache because this can be an early sign of an intracranial bleeding episode. Until the physician is contacted, the nurse must withhold the next dose of heparin.

Adrenocorticotropic hormone, plasma

Also called: (ACTH); Corticotropin

Specimen or type of test:

Purpose of the test

A plasma ACTH determination is obtained to diagnose Cushing’s disease and differentiate primary and secondary adrenal insufficiency.

Basics the nurse needs to know

Adrenocorticotropic hormone (ACTH) is produced and secreted by the anterior pituitary gland. Its secretion is under the control of the hypothalamus and the central nervous system by neurotransmitters and corticotropin-releasing hormone (CRH). ACTH, in turn, regulates the secretion of the glucocorticoids and androgens from the adrenal cortex.

The mechanisms of regulation of CRH, ACTH, and the adrenal hormones are multiple, and patterns of secretion of these hormones vary within the individual and among individuals. CRH and ACTH are excreted episodically and by circadian rhythm (remember crossing multiple time zones can affect a person’s circadian rhythm). Increases in ACTH levels cause increased levels of glucocorticoids and androgens in the blood within minutes. Generally, CRH, ACTH, and cortisol (the major glucocorticoid) levels are low in the evening and continue to decline for the first few hours of sleep. After 3 to 5 hours of sleep, the levels of the hormones increase and then peak after 6 to 8 hours of sleep. On waking, the hormone levels begin to decline. Superimposed on this circadian rhythm are episodic secretions. The hormone levels increase with exercise, eating, and stress.

A negative feedback mechanism also regulates the hypothalamic-pituitary-adrenal hormonal responses. As the cortisol level increases in the plasma, it inhibits both ACTH secretion by the pituitary gland and CRH secretion by the hypothalamus (Figure 10). The nurse needs to be aware of the feedback inhibition of CRH and ACTH, which occurs with exogenous administration of glucocorticoids.

Figure 10. Hypothalamic-pituitary-adrenal axis. Hypothalamic control of adrenal hormone secretion occurs through release of corticotropin-releasing hormone (CRH), which stimulates the secretion of adrenocorticotropic hormone (ACTH) by the pituitary gland. ACTH stimulates the adrenals to increase their secretion of cortisol. By a negative feedback mechanism, the increase in serum cortisol level suppresses the release of CRH and ACTH.

An increase or decrease in the production of ACTH will cause an increase or decrease in the glucocorticoid levels. A deficiency of ACTH will cause secondary adrenal insufficiency. An increase in ACTH will cause Cushing’s disease (Cushing’s syndrome is a primary adrenal disorder).

REFERENCE VALUES *

In morning (6 am-10 am): 25-100 pg/mL or SI: 25-100 pmol/L

In evening (9 pm-12 am): 0-50 pg/mL or SI: 0-50 pmol/L

^*Values vary depending on laboratory.

How the test is done

A venipuncture is done with chilled syringe and blood placed on ice and sent immediately to the lab.

Interfering factors

• Noncompliance with medication, diet, or activity restrictions

• Administration of radioactive scans within 7 days

• Traumatic venipuncture

• Delay in specimen being tested or frozen

• Ingestion of alcohol, amphetamines, calcium gluconate, corticosteroids, estrogen, lithium, or spironolactone

NURSING CARE

Nursing actions are similar to those used in other venipuncture procedures (see Chapter 2), with the following additional measures.

Posttest

• The patient resumes a normal diet, activity, and medication regimen. The nurse notifies the dietary department to bring the patient his or her meal.

Adrenocorticotropic hormone stimulation test

Also called: ACTH Stimulation Test; Rapid or Short ACTH Test; Corticotropin Stimulation Test; Cosyntropin Test; Cortrosyn Stimulating Test

Specimen or type of test:

Purpose of the test

The ACTH stimulation test is performed to diagnose primary and secondary adrenal insufficiency. It may also be done to assess outcome in patients in septic shock. A small increase in corticotropin in the simulation test indicates a poor outcome for patients in septic shock.

Basics the nurse needs to know

ACTH is secreted by the pituitary gland. Its target organ is the adrenal cortex, where it stimulates the secretion of glucocorticoids, aldosterone, and androgens. Synthetic ACTH, known as cosyntropin (Cortrosyn), normally has the same effect. It causes an increase in adrenal cortex hormones. A normal response excludes the diagnosis of primary adrenocorticoid insufficiency, because the gland was able to respond. A normal response will also rule out complete ACTH deficiency (secondary adrenocorticoid failure) because complete lack of ACTH causes adrenal atrophy, and the gland is unable to respond.

In an abnormal response, primary or secondary adrenal insufficiency may be present. Aldosterone levels may be measured to distinguish between the two forms. If no change occurs in the aldosterone levels after cosyntropin is given, primary adrenal insufficiency is present. With secondary adrenal insufficiency, aldosterone levels will increase by more than 4 μg/dL.

ACTH will also be secreted in response to insulin-induced hypoglycemia; therefore, insulin is another means to stimulate its secretion.

REFERENCE VALUES

Within 30 to 60 minutes, plasma cortisol increases to 18 to 20 μg/dL or SI: 500 to 550 npmol/L.

How the test is done

After the baseline plasma cortisol level is obtained, cosyntropin or insulin is given intravenously. Cosyntropin may be given intramuscularly if the patient is not hypotensive. After 30 to 60 minutes, another plasma cortisol level is obtained.

Significance of test results

Elevated values

Normal response

Unchanged values

Addison’s disease

Adrenal atrophy

Hypopituitarism

Alanine aminotransferase

Also called: (ALT); Glutamic-Pyruvic Transaminase (SGPT)

Specimen or type of test:

Purpose of the test

The alanine aminotransferase (ALT) test is used to detect hepatocellular injury or necrosis (injury or death of liver cells). It is the most specific of the transaminase enzyme tests to detect acute hepatitis from a viral, toxic, or drug-induced cause. It is used to help determine the source of jaundice. After an acute episode of hepatitis has abated, the persistence of an elevated ALT level suggests that the illness has not resolved and the patient is at high risk to progress to chronic hepatitis. Serial measurements are used to track the course of the hepatitis.

Basics the nurse needs to know

Alanine aminotransferase is a transaminase enzyme that is found in the cells of the liver and kidneys, and to lesser extents in the cells of the heart, skeletal muscle, and red blood cells. When cellular injury or necrosis occurs in the liver and other tissues that contain this transaminase enzyme, the enzymes leave the cytoplasm, pass through damaged cell membranes, and enter the serum. In acute hepatitis, the serum level rises dramatically, to a level of 20 times the normal value. In cases of obstructive jaundice, cirrhosis, and liver tumor, the ALT level rises mildly or moderately, from two to four times the normal value.

The ALT value also rises moderately as a result of myocardial infarction, heart failure, and shock. Mild skeletal muscle injury, as from trauma or surgery also causes a mild to moderate rise in the ALT level. A mildly elevated ALT level may be present because of obesity, particularly when there is fat accumulation in the abdomen. Fatty liver disease is the most common cause of liver disease in the pediatric population.

How the test is done

Venipuncture is performed to collect a sample of venous blood.

Albumin, serum

See Protein, Total, Serum on p. 522

Albumin, urinary

Also called: Protein Screen; Urine Screen for Albumin; Urinary Albumin, 24-hour collection

Specimen or type of test:

Purpose of the test

Urinary excretion of albumin is evaluated to assess renal function and to determine effectiveness of therapy in the management of urinary disease. Studies have shown that albumin in urine also can be used as a predictor of complications associated with diabetes mellitus.

Basics the nurse needs to know

Evaluation of protein in the urine is done as part of routine urinalysis or it may be done as a specific test to measure or monitor for proteinuria. In the healthy adult, the excretion of protein is so small that it is undetectable by routine methods of analysis. Proteinuria does not always mean there is renal disease. The proteinuria may be transient, as the result of factors such as strenuous exercise, dehydration, muscle injury, pregnancy, or severe viral infection. When the test is positive, retesting is done at intervals to determine if the result is transitory.

In urinary disorders, the origin of proteinuria may be from glomerular damage in the kidneys that alters filtration. Large protein molecules are filtered from the plasma by leaking through damaged glomerular membranes. It may also be due to tubular damage that alters reabsorption of small protein molecules. Additionally, protein may enter the urine from the lower urinary tract as in infection, inflammation, or bleeding from trauma or menstrual flow. The abnormal value of 30/mg/dL/24 hr or SI: 300 mg/L/24 hr or higher is considered a clinically significant abnormal value.

REFERENCE VALUES

Random specimen (microalbumin): <2 mg/dL

24-hour specimen: 10 mg/dL or less or SI: 100 mg/L or less

Reagent strip: Negative

How the test is done

Various methods are available for assessing urinary excretion of albumin. Reagent strips are sensitive to albumin, but not at very low levels. For a reagent strip analysis of albumin, a random urine specimen is collected in a clean container. A first voided urine specimen is preferred.

For microalbuminuria measurement, a 24-hour specimen of urine is used with no preservative in the collection container. The specimen is kept refrigerated and should be sent to the lab within 2 hours of its collection.

Interfering factors

• With reagent strips: Highly concentrated urine; highly alkaline urine; specimen contaminated with bacteria, blood, ammonium compounds (detergents), chlorhexidine (cleansers), or fabric softeners

• With turbidimetric method: Ingestion of cephalosporin, penicillin, sulfonamides, or tolbutamide; recent administration of radiocontrast dyes

NURSING CARE

Nursing actions are similar to those used in other urine collection procedures (see Chapter 2), with the following additional measures.

Health promotion

The nurse may need to instruct patients who have renal disorders or possible diabetes mellitus complications to test their urine daily for albumin using a reagent strip.

Pretest

• Care is dependent on the method of analysis. Check with the laboratory regarding the method and specimen required. A laboratory urine specimen container should be used. Ordinary household jars or containers can have residual detergent or cleanser contaminants.

Posttest

• Patient teaching.

If the patient is going to monitor his or her own urinary albumin at home, the nurse will assess the patient’s understanding of the purpose of home testing, the reading of the test results when compared with the manufacturer’s color chart of test results, and the need to notify the physician if albumin is present or if its concentration increases. Abnormal results are usually investigated in a follow-up by laboratory analysis and specific measurement of the protein amount.

• Instruct the patient to use the first voided urine in the morning. Warn the patient that any vigorous exercise before urine collection will increase the excretion of albumin in the urine and cause a false positive result. Teach the patient how to follow the manufacturer’s instructions for using the reagent strip. Timing varies by the manufacturer. Instruct the patient to keep the top on the reagent strip container.

Aldosterone, serum

Specimen or type of test:

Purpose of the test

The aldosterone level is used in the workup for hypertension and in the diagnosis of aldosteronism.

Basics the nurse needs to know

Aldosterone is a mineralocorticoid produced by the adrenal cortex and controlled primarily by the renin-angiotensin system. Renin secreted by the kidneys acts on angiotensinogen to convert it to angiotensin I. Later, angiotensin I is converted to angiotensin II. Angiotensin II stimulates the adrenal cortex to produce and secrete aldosterone. The aldosterone acts on the renal tubules to (1) increase sodium retention and thus increase fluid retention, which increases plasma fluid volume and blood pressure, and (2) to increase potassium excretion in urine (Figure 11).

Figure 11. Primary regulation of aldosterone secretion.

Another stimulant for aldosterone secretion is the serum potassium level. When serum potassium levels are elevated, increased secretion of aldosterone occurs, promoting greater urinary excretion of potassium.

The presence of high levels of aldosterone is called aldosteronism. Primary aldosteronism often is caused by adrenal adenoma (Conn’s syndrome). This condition is characterized by hypertension with hypokalemia and urinary potassium loss. Secondary aldosteronism is caused by nonadrenal disease that stimulates the adrenal cortex to produce and secrete excessive aldosterone.

In testing for serum aldosterone levels, a number of variables must be controlled to provide accurate results. A low-salt diet, an upright position, and stress all produce increased levels of aldosterone. A high-salt diet and a supine position decrease the serum levels.

If serum aldosterone levels are elevated, primary aldosteronism can be confirmed with a captopril, fludrocortisone, or saline stimulation test. With the administration of captopril, fludrocortisone acetate (Florinef) or intravenous saline, the secretion of aldosterone is suppressed in normal patients and in patients with secondary aldosteronism, but serum levels rise in patients with primary aldosteronism.

How the test is done

A venipuncture is done and the specimen is immediately placed on ice and sent to the lab. The vascular site may be any peripheral vein. The patient may be in a supine or an upright position. Using interventional radiographic techniques, a blood sample from the adrenal vein may be done to confirm the diagnosis of adrenal adenoma.

Other diagnostic methods include administering 2 L of normal saline over 4 hours before the blood test or drawing the blood on the third day after the administration of fludrocortisone acetate, a synthetic mineralocorticoid.

Interfering factors

• Licorice intake

• Uncontrolled sodium intake

• Postural changes

• Warming of the specimen

• Recent radioisotope administration

• Loop diuretics

NURSING CARE

Nursing actions are similar to those used in other venipuncture procedures (see Chapter 2), with the following additional measures.

Aldosterone, urinary

Specimen or type of test:

Purpose of the test

The main use of the urine aldosterone test is to help identify primary hyperaldosteronism caused by adrenal adenoma.

How the test is done

A 24-hour urine specimen is collected in a clean plastic container. Some laboratories add a measured quantity of preservative (boric, acetic, or hydrochloric acid) to the container before the start of the collection period.

Unlike serum aldosterone levels, positioning does not affect urinary aldosterone levels.

Interfering factors

• Excess salt intake

• Recent administration of radioisotopes

• Licorice intake

• Failure to collect all the urine

• Warming of the specimen

• Diuretics (loop or thiazides)

• Oral contraceptives

NURSING CARE

Nursing actions are similar to those used in other 24-hour urine collection procedures (see Chapter 2), with the following additional measures.

Posttest

• On the requisition slip, write the pretest sodium diet.

• Arrange for prompt transport of the cooled specimen to the laboratory.

Alkaline phosphatase

Also called: (ALP)

Specimen or type of test:

Purpose of the test

Serum alkaline phosphatase (ALP) testing is a nonspecific indicator of liver disease, biliary tract obstruction, bone disease, or hyperparathyroidism. It is part of a battery of tests that evaluate liver function. It also serves as a tumor marker by indicating rapid cell growth or accelerated function caused by malignancy of the liver or bone.

Basics the nurse needs to know

ALP is an enzyme located primarily in the osteoblast cells of the bone, in the hepatocytes of the liver, and to a lesser extent in the intestines, kidney, and placenta. A high level of ALP usually means that a specific organ or tissue has increased the manufacture or release of the enzyme. The ALP enzyme is normally excreted via the biliary tract, but if there is any blockage in the biliary tree, the hepatocytes of the liver produce more ALP.

The ALP level will rise with increased activity from liver disease, biliary tract obstruction, or bone disease. In serious or advanced liver or bone disease, the ALP value can rise dramatically to 10 to 12 times the normal value. Additional transaminase enzyme tests can help identify the source of the ALP elevation. When the cause of an elevated ALP arises from liver disease, the alanine aminotransferase (ALT) and aspartate aminotransferase (AST) test results are also mildly elevated. With an elevated ALP result that is caused by bone disease, however, there is no associated elevation of the ALT or AST levels.

The normal values for children vary widely because of growth activity. During adolescence, the normal value of ALP may be 3 times higher than that of a normal adult. During normal skeletal growth, additional ALP leaks into the serum from the active osteoblast cells of the bones and causes elevated ALP results.

How the test is done

Venipuncture is performed to collect a sample of venous blood.

Allergy tests, skin

Also called: Skin prick or skin puncture test, Intradermal skin test

Purpose of the test

Skin testing is done to identify a sensitivity response to specific allergens in the environment, food, or medications. Once sensitivity to a specific allergen is identified, the information is considered along with the clinical history to determine if an allergy exists. With accurate diagnosis, medical treatment will be more specific and effective.

Basics the nurse needs to know

Allergens are substances in the environment that have the potential to cause an allergic reaction when they enter the body or touch the skin of a sensitized person (Box 4). Sensitization means that specific IgE antibodies are present, but an allergic reaction depends on other variables such as whether the individual comes in contact with that specific allergen. If an allergic reaction starts, there is a rapid release of Immunoglobin E (IgE) antibody and histamine from the mast cells and symptoms emerge. This response will continue until all allergens are destroyed by the IgE antibody and cleared from the body. Allergy skin testing is a very effective method to identify which allergen is the cause of the sensitivity reaction. There are several methods of skin testing available. The two methods discussed in this section are the skin prick method and the intradermal method. Each of these tests uses very small doses of antigens that are introduced into the skin; then the examiner measures the amount of allergic response. In addition, the patch skin test can be done by placing suspected allergens on the skin surface and measuring the allergic response from the contact. (See Patch Test on p. 480). Additionally, allergy testing may be done on a specimen of blood; it involves a quantitative measure of the IgE antibody response to specific allergens. (See Immunoglobin E Antibody on p. 394).

The skin prick method is preferred for the initial testing of the skin. It is safer because it causes fewer systemic reactions. This method can screen for a number of suspected allergens at the same time. The intradermal test method is more sensitive and accurate than the skin prick method. It is used in follow-up when a previously negative result occurs with the less sensitive skin prick method. It is also often used to test for an allergy to particular medications and for an allergy to insect venom, such as bee or wasp stings. There is a potential for a systemic reaction to the allergen that includes risk of anaphylaxis.

A positive skin test result is a wheal and flare response. The wheal is a localized area of very pale or white raised tissue that itches. The flare is the erythematous area around the wheal. A positive response is a raised wheal with a diameter of 3 mm or more and a flare of 10 mm or more across the longest diameter. The skin reactions are visible and measured after 15 to 20 minutes.

REFERENCE VALUES

Skin prick method: Negative in response to the specific allergens tested

Intradermal method: Negative in response to the specific allergens tested

How the test is done

For either skin prick or intradermal methods of testing, negative and positive control samples are implanted at the beginning of the test. The control samples ensure accuracy in the interpretation of the result. The inner aspect of the forearm is the preferred site for skin testing. Each antigen inoculation is identified with a label on the skin near the site.

Skin prick method: A drop of commercially prepared antigen solution is placed on the test stylus device. The stylus device is pushed down gently to prick the skin and allow the allergen to barely penetrate the epidermis. The stylus may have a single point for single allergen testing, or it may be a multitest device with up to 10 points to test the corresponding number of different allergens. Alternatively, a droplet of allergen is placed on the skin and a very small sterile needle is used (Figure 12).

Figure 12. Allergy skin testing. The percutaneous skin prick method of testing. A, The drop of allergen is placed on the skin and the 27-gauge needle (bevel up) is placed through the allergen drop into the superficial epidermis. B, The needle pricks the skin at a 45-degree angle, allowing the allergen to come into contact with the sensitized mast cells in the epidermis, and then lifted up. The dermis is not penetrated and bleeding at the site is nonexistent or minimal.

(From Pfenninger JL, Fowler GC: Pfenninger and Fowler’s procedures for primary care, ed 3, St Louis, 2011, Mosby.)

Intradermal method: A small dose of very diluted allergen preparation is injected intradermally with a fine needle and 0.5 to 1.0 mL syringe.

Significance of the test results

Positive values

Sensitivity to specific allergens

Interfering factors

• Current use of antihistamine medication

NURSING CARE

Pretest

• Perform a detailed clinical history, including the age of the person, his or her living environment, occupation, and preferred activities. All of these factors can give clues about the type of allergen that may be responsible for the allergy. The patient may be able to describe previous allergy-related symptoms, when the episode occurred, and possibly what caused it to occur.

• In the history, include a list of current medications the patient takes because some of the medications will alter the skin response in allergy testing. Additionally, some of the medications may have already caused an allergic response.

• A physical examination is performed, particularly noting any skin reactions, rashes, or other allergy symptoms that may be present.

• Instruct the patient to discontinue the use of antihistamine medications, such as diphenhydramine (Benadryl) or chlorpheniramine (Chlor-Trimeton), at least 24 hours before having the skin tests performed because these drugs would mute the test results.

• Obtain a signed, informed consent.

• Because anaphylaxis can occur during or shortly after the allergens are administered, the nurse ensures that a crash cart and emergency medications/equipment are nearby.

During the test

• Observe the patient for complications during and after the testing period, particularly when using the intradermal test method. The allergic responses can be moderate to severe or fatal. The adverse reactions can be of rapid onset or delayed until after completion of the tests. Mild or moderate reactions consist of the onset of erythema (overall redness of the skin from inflammation), edema, induration (a hard area of tissue) and dysesthesia (a change in any sense, such as pain on gentle touching of the skin). A severe reaction is rare. It is usually a hypersensitivity reaction and is associated with drug (medication) testing. Shock, respiratory distress, and cardiac arrest can occur. Oxygen, emergency drugs, and CPR may be needed.

Posttest

• Patient teaching.

Once the allergen is identified, the primary approach to patient teaching is that the patient should avoid exposure to the substance that will act as an “allergy trigger” and cause an allergic response. For a food allergy, the nurse can teach the patient to identify any hidden sources of allergens, such as by reading labels on canned or prepared food and making inquiries if ordering food in a restaurant.

If the patient has already had a life-threatening reaction to a particular allergen as a venomous sting or a particular medication, instruct the patient to carry an injectable device that contains epinephrine. The patient needs to learn how to use it, when to use it, and where to get additional medical care as quickly as possible. Some patients may choose to wear a medical bracelet that identifies the severe allergy and provides other pertinent information.

• For hospitalized patients, the information about any allergy must be posted in the patient ’s record and on a special allergy identification bracelet worn by the patient.

Alpha 1 antitrypsin

See Protein Electrophoresis, serum on p. 520.

Alpha-fetoprotein

Also called: (AFP), α-fetoprotein; fetoprotein

Specimen or type of test:

Purpose of the test

In the nonpregnant patient, AFP is a tumor marker for primary cancer of the liver (hepatoma). It is used to help with the diagnosis and to monitor the effect of chemotherapy treatment on that tumor. It is also used as a tumor marker and to help with diagnosis and staging of some types of testicular cancer.

In a pregnant woman, serum AFP serves as a screening test for neural tube defects in the fetus. Neural tube defects in the fetus include spinal bifida, myelomeningocele, and anencephaly. It is also part of the multiple marker screening test that detects fetal Down syndrome in the pregnant woman.

Basics the nurse needs to know

In the blood of healthy, nonpregnant adults, AFP is present in very small amounts. If the liver has been injured by trauma, exposure to chemical toxins or the hepatitis virus, the AFP level will rise moderately as healing and regeneration of liver cells occurs.

As a tumor marker for primary hepatoma, the serum level rises to values of 1000 ng/mL (SI: 1000 μg/mL) or dramatically higher. When the test is used to monitor the response of the testicular tumor to chemotherapy treatment, a rising AFP value indicates additional growth of the tumor and a falling value indicates a favorable response to the chemotherapy treatment.

In a pregnant woman, the fetus produces the AFP and it is, therefore, present in the amniotic fluid and the maternal serum. The maternal serum level increases throughout the pregnancy and in the third trimester rises to 500 ng/mL (SI: 500 μg/L). The pregnant African American woman has a normal value that is 10% to15% higher than the Caucasian woman throughout the pregnancy. The normal value for the pregnant woman who has insulin-dependent diabetes is 20% lower than the average normal value.

For prenatal screening, the best time to draw the maternal blood is in the 16th to 18th week of the pregnancy, but the specimen can be drawn during the 15th to 21st week. An abnormally elevated value occurs with open neural tube defect and some other congenital defects in the fetus. The test, however, can have false positive results because the calculation of the normal value is based on the gestational age of the fetus.

The gestational age is best measured by ultrasound. Often, however, the calculation is based on the mother’s estimate of when her last menstrual period occurred and this may not be precise. Because of the possibility of error, a positive screening test result is considered only suggestive of an abnormality in the fetus. Additional evaluation by ultrasound is recommended, and based on the results of the pregnancy ultrasound, amniocentesis may be needed. With a follow-up pregnancy ultrasound, the examination focus is on the fetal spine and cranium. With amniocentesis, the analysis of the amniotic fluid would provide accurate information about the condition of the fetus. Normal findings of these additional tests demonstrate that no neural tube defect exists (Figure 13).

Figure 13. Pregnancy ultrasound. The varying densities and compositions of tissue allow visualization of the uterine contents. A, A normal 4-month-old fetus. The fetal heart (FH) is identified. B, The normal spinal structure of a 4-month-old fetus.

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Tags: Saunders Nursing Guide to Diagnostic and Laboratory Tests

Feb 18, 2017 | Posted by admin in NURSING | Comments Off

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