C

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Calcitonin

Also called: (CT); Thyrocalcitonin

Specimen or type of test:

Purpose of the test

A calcitonin determination is usually performed to diagnose medullary carcinoma of the thyroid gland.

Basics the nurse needs to know

Calcitonin is a hormone produced and secreted by the parafollicular cells (C cells) of the thyroid gland. It may also be produced and secreted by ectopic sites such as the lungs, intestines, pituitary gland, and bladder. The action of calcitonin is to inhibit bone reabsorption, inhibit calcium absorption in the gastrointestinal tract, and increase calcium and phosphate excretion from the kidneys. It is believed that calcitonin is not secreted until plasma calcium levels reach 9.3 ng/dL.

To assess familial medullary cancer in relatives of patients with the cancer, a provocation test (also called a stimulation test) may be performed. Calcium chloride is given intravenously over 10 minutes, or pentagastrin is given intravenously over 5 to 10 minutes. Patients with medullary cancer will respond to these stimulants with excessive secretion of calcitonin.

How the test is done

A venipuncture is performed. Calcitonin is measured using radioimmunoassay (RIA).

Calcium, total and ionized, serum

Also called: Total calcium (CA); Ionized calcium (Ca1)

Specimen or type of test:

Purpose of the test

The total serum calcium or ionized (free) calcium levels are used to assist in the diagnosis of acid-base imbalance, coagulation disorders, pathologic bone disorders, endocrine disorders, cardiac arrhythmia, and muscle disorders.

Basics the nurse needs to know

Calcium is one of the essential mineral elements of the body and is needed for bone structure and for the process of bone formation. Almost all of it is concentrated in bone, with the remainder of the body’s calcium present in the cells or extracellular fluids, including the serum. Most of the serum calcium is either physiologically active in a free or ionized state or it is bonded to albumin and other plasma proteins. In the serum and other extracellular fluids, the normal level of ionized calcium is maintained in homeostatic balance by the actions of the small intestine, bones, and kidneys.

Serum calcium is needed for many physiologic functions, including coagulation of the blood, excitation of cardiac and skeletal muscle, maintenance of muscle tone, conduction of neuromuscular impulses, and synthesis and regulation of the endocrine and exocrine glands. On the cellular level, calcium preserves the integrity and permeability of the cell membrane, particularly for sodium and potassium exchange.

Elevated values

An elevated level of calcium in the blood is called hypercalcemia. It causes neuromuscular hypoactivity and alters the function of most body organs. Hypercalcemia can be a life-threatening complication. Hyperparathyroidism and malignancy are the most common causes of hypercalcemia.

Decreased values

A decreased level of calcium in the serum is called hypocalcemia. It causes neuromuscular hyperactivity, affecting many organs and functions. Very low calcium levels also can be life threatening. Total serum calcium is lowered in conditions that decrease plasma proteins, impair intestinal absorption, alter renal filtration and resorption functions, or decrease the amount of parathyroid hormone.

REFERENCE VALUES

How the test is done

Adult: Venipuncture is performed to collect venous blood.

Infant: A capillary pipette is used to collect capillary blood via the heelstick method.

Interfering factors

• Upright position or prolonged activity before the test

• Prolonged storage of the blood specimen

NURSING CARE

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

Posttest

• Arrange for prompt transport of the specimen to the laboratory. The analysis must be performed on a fresh sample to prevent a false elevation of the calcium value.

Nursing response to critical values

The nurse must notify the physician of any test result in the abnormal, critical value range. The nurse should also take the patient’s vital signs and assess for specific manifestations that occur with calcium imbalance.

Hypocalcemia.

The very low serum calcium can induce depression or psychosis, laryngeal stridor, tetany, convulsions, hypotension, and a weak, thready pulse. The patient will have hyperactive reflexes and positive Trousseau’s and Chvostek’s signs (Table 6). A severe decrease to 6 mg/dL (SI: 1.5 mmol/L) or less can be life threatening.

Table 6 Nursing Assessment for Hypocalcemia

Test	Method	Positive result
Trousseau’s sign	Apply a blood pressure cuff to the arm. Inflate the cuff to 10 mm above the patient’s systolic pressure for 3 minutes. Observe the hand. Then deflate the cuff.	When the serum calcium level is low, the patient’s hand will develop a carpal spasm. The first three fingers extend rigidly. The fourth and fifth fingers flex and curl toward the palm of the hand.
Chvostek’s sign	Use the tip of the index or middle finger to tap just beneath the cheekbone (zygoma) and towards the ear.	When the serum calcium level is low, the same side of the face will demonstrate repeated tics or involuntary spasms of the facial muscles.

Hypercalcemia.

The very high serum calcium level can induce polyuria, anorexia, nausea, tachycardia in an early stage or bradycardia in a later stage, muscle weakness, lethargy, and absent deep tendon reflexes. A severe elevation of 14 mg/dL (SI: 3.5 mmol/L) or more is likely to induce coma and can cause death from a cardiac arrest.

Calculus analysis

Also called: Kidney Stone Analysis; Renal Calculus Analysis

Specimen or type of test:

Purpose of the test

The analysis of urinary calculi is used in the workup for nephrolithiasis. It determines the chemical composition of the stone and the metabolic factors that result in stone formation.

Basics the nurse needs to know

A renal calculus is commonly called a stone. It forms in the renal pelvis; descends through the ureter, bladder, and urethra; and exits from the body in urine. Calculi are of various sizes, textures, colors, and chemical compositions. Common chemical compositions are: calcium, struvite, uric acid, and cystine. The composition of the stone will affect treatment to prevent reoccurrence.

Calcium stones are the most common type of renal calculi. These calculi are caused by excess calcium in the urine and consist of calcium phosphate, calcium oxalate, or a combination of the two chemical salts. These dark-colored stones are usually hard and have a rough surface. The underlying causes of calcium stone formation are thought to be increased intestinal absorption of dietary calcium, poor renal tubular resorption of calcium, a loss of calcium from bone, or any combination of these factors. The pH of the urine is often >6.0.

Struvite stones are sometimes called infection stones because of their association with chronic urinary tract infection. It is not known whether the stone causes the infection to occur or the infection causes the stone to form. These pale stones are usually large and soft. They are also called a staghorn calculus because of their characteristic shape. The chemical composition of struvite stones is magnesium ammonium phosphate and carbonate apatite. Struvite stones are sometimes called phosphate stones based on their chemical composition. The pH of the urine is often >6.0.

Uric acid stones consist of uric acid and urate crystals. They are yellow-brown and moderately hard. They form in the presence of excess uric acid and concentrated acidic urine. Underlying causes include high intake of food that is high in purine, primary gout, dehydration, and some medications, including thiazide diuretics and salicylates. The pH of the urine is acidic.

Cystine stones occur rarely. They are dark yellow-brown and greasy. Their formation is caused by an autosomal recessive inborn error in metabolism that impairs the absorption of amino acids. Because of this deficit in metabolism, cystine and other amino acids are excreted in urine. The precipitate forms both crystals and stones.

REFERENCE VALUES

No kidney stones are present in the urine.

How the test is done

All urine is strained through a gauze strainer or a fine mesh sieve. Any stones that are recovered are placed in a glass bottle or plastic container, and are sent to the laboratory for qualitative analysis.

Significance of test results

Abnormal values

Hyperparathyroidism

Primary cystinuria

Urinary tract infection

Other infection

NURSING CARE

• The nurse sends the stone to the laboratory in the labeled container. If the stone is enmeshed in the gauze, place both the stone and the gauze in the container.

• Specify on the requisition form that the source of the stone is urinary. Include patient ’s identification and the date and time that the stone was passed. The same identifying information is placed on the specimen container.

Cancer antigen 125

Also called: CA 125

Specimen or type of test:

Serum, body fluids

Purpose of the test

In patients with cancer of the ovary, this test is used to monitor the response to treatment or the progression of the disease.

Basics the nurse needs to know

Cancer antigen 125 (CA 125) is a tumor marker for ovarian cancer. Normally, this antigen is present in small amounts in the serum of healthy women. It will be present or rise slightly with menstruation, the first trimester of pregnancy, and with endometriosis. If ovarian or endometrial cells are destroyed by cancer or the cancer begins to grow, the persistently increasing level of the antigen can be detected in the blood. Because of the lack of specificity and sensitivity, this test cannot be used as a screening test for the general population. It is, however, a very helpful and reliable test to monitor the activity of known cancer of the ovary. A serum value greater than 35 U/mL (SI: >35 kU/L) is positive and correlates with malignancy.

How the test is done

Venipuncture is performed to collect a sample of venous blood.

Interfering factors

• Menstruation

• Recent radioisotope scan or abdominal surgery

NURSING CARE

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

Pretest

• This test should be scheduled no sooner than 3 weeks after abdominal surgery to avoid a false positive result. The test should also be scheduled before or at least 7 days after any radioisotope scan so that the radioisotopes of the scan will not interfere with the test methodology. The test should not be done during the woman’s menstruation because the value will be much higher at that time.

• For the patient with a history of cancer, provide empathetic support. Her anxiety level is likely to be high because of the implications of a potentially elevated test result.

Posttest

• When the patient with a known history of ovarian cancer has a persistently rising level of cancer antigen 125, a high probability exists that the cause is progression or recurrence of the malignancy. Before new treatment is instituted, additional diagnostic testing is indicated to locate metastasis. Provide continuing emotional support to help the patient cope during the stress of additional testing and in the decision making that is part of the overall treatment plan.

Capillary glucose/sugar monitoring

See Glucose, Capillary on p. 336.

Capnogram

Also called: Exhaled Carbon Dioxide; Capnography; End-Tidal Carbon Dioxide; ETco₂; (PETco₂) Partial Pressure End Tidal CO₂

Specimen or type of test:

Purpose of the test

Monitoring exhaled carbon dioxide (CO₂) permits continuous evaluation of alveolar ventilation, reducing the number of ABG determinations needed. ETco₂ may be used to evaluate ventilator changes and weaning parameters from mechanical ventilation. It will confirm endotracheal intubation because no capnographic waveform will occur if the tube is in the esophagus.

Capnography may be used to monitor the patient during an apnea test. An apnea test is done to diagnosis brain death. This test requires the observation of spontaneous respiration when the arterial CO₂ is above 60 mm Hg.

Basics the nurse needs to know

Capnography provides a CO₂ waveform, which visualizes CO₂ elimination patterns during exhalation and a total percentage of CO₂ exhaled per breath. CO₂ is measured at the end of exhalation because at this point the exhaled CO₂ approximates arterial CO₂ levels. With normal perfusion of the lungs, arterial CO₂ will be a few millimeters higher (5 mm Hg) than end-tidal CO₂ (ETco₂). When perfusion is not adequate, this assumption cannot be made. Figure 28 shows a typical tracing of a capnogram.

Figure 28. Capnographic tracing. On exhalation, the capnographic tracing shows a rapid rise in carbon dioxide followed by a plateau. At the end of exhalation, the end-tidal carbon dioxide level is obtained. As inspiration begins, there is a dramatic decrease in carbon dioxide.

How the test is done

Exhaled CO₂ is measured with exhaled gas analyzers. These analyzers measure the CO₂ by mass spectrometry or infrared analysis. Mass spectrometry requires aspiration of exhaled gas, whereas the infrared gas analyzer is usually attached to the exhalation tubing on a ventilator. The recorded value refers to the amount of infrared light absorbed by the exhaled breath. The higher the CO₂ level, the more infrared light is absorbed and the higher the reading.

For endotracheal tube placement, disposable colorimetric devices are available for single use.

Carbohydrate antigen 19-9

Also called: CA 19-9; Cancer Antigen CA19-9

Specimen or type of test:

Purpose of the test

Carbohydrate antigen 19-9 (CA 19-9) is a tumor marker that is used in preoperative staging for cancer of the pancreas. It is also used to monitor the course of pancreatic cancer, the response to treatment, and to predict recurrence.

Basics the nurse needs to know

CA 19-9 is an antigen made by the pancreas, liver, colon, and other tissues. The antigen appears in the serum when these source tissues undergo healing or when there is a tumor growing in that organ or tissue. This tumor marker is most accurate in cases of pancreatic cancer. The serum level does not rise in an early stage of disease, but is most accurate in the late stages of cancer or during recurrence.

Malignancy causes this test result to rise dramatically. Tumors of the pancreas can cause the serum level to rise to >1000 units/mL (SI: >1000 kU/L). Any result greater than 300 units/L (SI: 300 kU/L) is an indicator that the pancreatic cancer may be too advanced for surgical removal.

After treatment of the cancer of the pancreas, CA 19-9 is used to monitor the patient’s condition. A renewed elevation of CA 19-9 indicates that the cancer has returned. The serum level will rise before clinical symptoms appear.

Benign conditions of the pancreas, liver, and gall bladder also can cause an elevation of CA 19-9. In benign disease, the elevation is much lower than the dramatically high elevations associated with cancer. This test has a lack of specificity because it cannot distinguish between benign and malignant causes of hepatobiliary and pancreatic disease and various other diseases. Thus, because of false-positive results in benign conditions, this tumor marker does not have a clear role in the management of cancer patients (Marrelli, Caruso & Pedrazzani, 2009).

REFERENCE VALUES

Adult: <37 U/mL or SI: <37 kU/L

How the test is done

Venipuncture is used to collect a sample of venous blood.

Interfering factors

NURSING CARE

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

Pretest

• Provide emotional support for the patient. Ongoing testing for cancer and tumor markers can create anxiety because of the implications of an elevated result.

Posttest

• When the elevated test result indicates recurrence of cancer, the patient will need emotional support. In some cases, there may be additional treatment options, but in cases of recurrent cancer of the pancreas, the prognosis is bleak. The nurse can use listening skills and empathy to allow the patient to verbalize or express emotion. As the patient becomes aware of declining health, he or she may express denial or anger, or may become depressed. Some will express hope and others will begin to make decisions regarding their future. Listening to the patient can provide the cues as to what the patient believes and how he or she wants to use the time that remains.

Carbon dioxide, total

Also called: tCO_2,; TCO_2; CO₂ Content

Specimen or type of test:

Whole blood, serum, plasma

Purpose of the test

The total carbon dioxide (TCO₂) determination is used to help evaluate acid-base balance and the bicarbonate buffer system.

Basics the nurse needs to know

Total CO₂ measures the combined forms of CO₂ in the blood. The largest component is bicarbonate ion, composing 90% of the total CO₂ content in the blood. The total CO₂ content provides the principal extracellular buffer system, which is called the bicarbonate carbonic acid buffer. Buffer systems are needed in the regulation of acid-base balance. The concentration of carbon dioxide is controlled by the lungs, and the concentration of bicarbonate is controlled by the kidneys.

Elevated values

An elevated serum level of TCO₂ is called hypercapnia. It often is caused by poor CO₂ excretion by the lungs or an inadequate respiratory drive.

Hypercapnia is associated with respiratory acidosis, CO₂ retention, and metabolic alkalosis.

How the test is done

Venipuncture or arterial puncture is done to collect a sample of venous or arterial blood.

A capillary pipette is used to collect capillary blood.

Carboxyhemoglobin

Also called: COHb

Specimen or type of test:

Purpose of the test

Carboxyhemoglobin measures the amount of carbon monoxide that is in the blood, bound to hemoglobin molecules.

Basics the nurse needs to know

Carbon monoxide enters the body by inhalation of exhaust from the burning of fossil fuels, including gasoline, kerosene, coal, charcoal, wood, and oil. The exhaust enters the air from a defective heater, furnace, stove, or generator, exhaust from an automotive vehicle, or by burning fuel in an area with poor ventilation. The exposure can be accidental or a suicide attempt. The person who is in fire may also breathe a substantial amount of carbon monoxide in the smoky air. Carbon monoxide is present in tobacco smoke and may also come from industrial sources. Depending on the amount of exposure, carbon monoxide poisoning can kill in minutes or hours.

The hemoglobin molecule of a red blood cell has four receptor sites that will bind with oxygen molecules for transport of the oxygen to cells. When carbon monoxide is present in the blood, the hemoglobin has a powerful affinity to quickly attach the carbon monoxide instead of oxygen. The combination of carbon monoxide and hemoglobin form a compound called carboxyhemoglobin that cannot transport oxygen. As carboxyhemoglobin accumulates in the blood, tissue hypoxia begins to develop. In addition, the increasing accumulations of carboxyhemoglobin cause a shift of the hemoglobin-oxygen dissociation curve to the left, adding to the anoxia.

In laboratory measurements, the amount of carboxyhemoglobin in the blood is expressed as the percentage of hemoglobin that is saturated with carbon monoxide or the fraction of the whole that is saturated. As the amount of carboxyhemoglobin increases to 20% to 30% of hemoglobin saturation, symptoms of carbon monoxide poisoning appear. In children, lower concentrations may be toxic (McPherson & Pincus, 2007).

How the test is done

Venipuncture is performed to collect a sample of venous blood.

Significance of the test results

Evaluated values

Carbon monoxide poisoning

Hemolytic disease

Interfering factors

NURSING CARE

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

Pretest

• If the blood specimen can be drawn before oxygen therapy is started, an accurate carboxyhemoglobin value will be identified. Oxygen administration accelerates the elimination of carbon monoxide from the body and the carboxyhemoglobin value will begin to decline.

Posttest

• Patient teaching.

At the time of discharge after a low level of accidental exposure in the home, instruct the patient to get plenty of fresh air in the next few hours. In addition, instruct the patient not to return home until the furnace and all gas appliances are checked by a professional. Keep all windows opened to eliminate any residual carbon monoxide that is present.

Nursing responses to critical values

The patient may already have a toxic level of carbon monoxide poisoning at the time of admission for emergency treatment. The nurse assesses for symptoms including headache, nausea, dizziness, mental confusion, and elevations of the pulse, blood pressure, and respiratory rate. Late signs are the presence of the characteristic cherry red skin, loss of consciousness, hypotension, coma, seizures, and cardiac arrest (Goldstein, 2008). The nurse prepares to administer prescribed 100% pure oxygen via a tight-fitting, nonrebreather mask. Other emergency measures may be needed, such as intubation and cardiac/respiratory support.

Carcinoembryonic antigen

Also called: CEA

Specimen or type of test:

Serum, body fluid

Purpose of the test

Carcinoembryonic antigen (CEA) is a tumor marker used to monitor for and detect recurrence of colorectal, breast, and gastric cancer. It also may be used to measure the extent of malignant disease and help in the staging of the cancer.

Basics the nurse needs to know

In cancer, the necrosis of malignant tissue permits large amounts of this antigen to leak out of the tumor and enter the blood and body (effusion) fluids. An elevated value of serum CEA indicates that there is extension or recurrence of cancer at the primary site or metastases to a distant site (often liver, lung, or bone). The CEA value often rises many months before other laboratory tests become abnormal and before the patient experiences symptoms.

Elevated levels can occur in benign disease, but the test values are in a lower range than those of malignancy. Smokers have a normal value that is higher than nonsmokers, but do not necessarily have benign or malignant disease. A CEA value of >20 ng/mL (SI: >20 mcg/L) usually indicates cancer at a primary or metastatic site.

Interpretation of the test results is made with consideration of when the test is done. If the CEA value is normal after surgical removal of the cancer, the information means that no new cancer is growing. If the CEA value rises in the weeks, months, or years after surgical removal, it provides very early warning that cancer has recurred in the primary or metastatic site. Additional testing to locate the site of the cancer and additional cancer treatment are likely. In colorectal cancer, a preoperative elevation of CEA indicates a poorer long-term prognosis.

REFERENCE VALUES

Adult, nonsmoker: <3.0 ng/mL or SI: <3.0 mcg/L

Adult, smoker: <5.0 ng/mL or SI: <5 mcg/L

How the test is done

Blood: Venipuncture is used to obtain a sample of venous blood. Blood specimens are generally done before surgery, 4 weeks postoperatively, and at regular intervals thereafter for 5 years.

Body fluid: A sample of the body fluid is collected by the physician during a diagnostic procedure, such as a thoracentesis, or paracentesis .

Interfering factors

• Recent administration of radioisotopes

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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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