Laboratory Values and Diagnostics



Laboratory Values and Diagnostics


Kathleen Jett




Learning Objectives


On completion of this chapter, the reader will be able to:


1. Identify the laboratory values that increase or decrease with normal aging.


2. Understand the implications and deviations of key abnormal laboratory values in the older adult.


3. Define cautions the nurse should take when interpreting laboratory values in the older adult.


4. Discuss strategies that can be used to maximize the quality of laboratory testing.


5. Discuss the key laboratory tests used to monitor common health problems.


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The nurse’s knowledge related to laboratory values and diagnostics tests takes on special meaning when working with older adults. The older a person is, the more difficult is the interpretation of findings and the more important are the nurse’s skills. These skills include basic interpretation and those required to obtain or supervise specimen collection, to the timing of the procedure and awareness of influences on the results. For nurses working in long-term care settings, knowledge of interpretation is especially important to ensure that the persons with abnormalities in their laboratory results are treated promptly and appropriately. Advanced practice nurses are responsible for diagnostic and prescriptive responses to these results.


Laboratory findings are often reported in relationship to a range of normalized values or reference ranges referred to as “normal limits” within specific parameters. Most laboratory findings and their meanings are the same for older and younger adults. However, deviations from the norm are much more likely to occur and therefore special diligence is needed. Understanding laboratory values in older adults is complicated by the number of concurrent chronic diseases and medications, which cloud the interpretation. We must take the knowledge of normal changes and consider the person in terms of his or her unique health status and needs.



Hematological Testing


Hematological testing refers to that which is associated with the blood and lymph and their component parts. Blood is composed of red blood cells, white blood cells, and cell fragments called platelets. Together the cells float in a fluid matrix called plasma. Although several age-related hematological changes occur mainly because of changes in the bone marrow, few of these are clinically significant (Freedman, 2009-2010a). However, a number of disorders commonly seen in later life are diagnosed or monitored through hematological testing. Several conditions also affect the results, such as dehydration, inadequate nutrition, infections, and inflammation.


Several laboratory tests are used to measure and diagnose hematological health. The hemogram includes counts of platelets, white blood cells, and red blood cells, as well as the calculation of a hematocrit and indices. A complete blood count (CBC) is a hemogram plus a differential count. One of the basic laboratory measures that reflect hematopoietic functioning is iron studies. The erythrocyte sedimentation rate uses red blood cells in the measurement of systemic inflammation.



Red Blood Cell Count


The primary function of red blood cells (RBCs, erythrocytes) is to transport molecules of hemoglobin, which in turn transports and exchanges oxygen and carbon dioxide throughout the body. Because the erythrocytes have no nucleus of their own, they cannot reproduce. With the red blood cell’s average life span of 120 days, the body is in constant need of replenishment. Red blood cells are produced primarily by the bone marrow, the tissue found inside the spaces of the long bones. There is no indication that there is a change in RBCs in aging; however, the speed at which new blood cells can be produced in late life is reduced (decreased marrow reserve). This becomes a potential problem with a loss of blood such as after phlebotomy or frank bleeding. Recovery from the loss takes much longer, increasing the risk of falling, delirium, and other geriatric syndromes. Older adults are up to six times more likely to develop anemia, because of the combination of common diseases and medications taken. The prevalence of anemia is in the 8% to 22% range in older adults, depending on age and concurrent conditions; and is most often normocytic with multifactorial causes, or an anemia of chronic disease (Auerhahn et al., 2007). The categorization of an anemia involves multiple measurements and interpretation and includes the components described in this section, as well as the calculated cell indices of mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and red blood cell distribution width (RDW). A detailed discussion of these indices is beyond the scope of this chapter.



Hemoglobin and Hematocrit


Laboratory results including hemoglobin and hematocrit are commonly reviewed. Hemoglobin is the main component of the red blood cell. It is a conjugated protein whose main function is to transport oxygen from the lungs to the tissues, and carbon dioxide from the tissues to the lungs. It contains iron and the red pigment porphyrin. The iron combines easily with both oxygen and carbon dioxide. Each saturated gram of hemoglobin carries 1.39 mL of oxygen. It is the hemoglobin concentration, not the red blood cell count, that is used as an indicator for anemia. A hemoglobin level equal to or less than 5 g/dL, or more than 20 g/dL, is considered a “critical value,” that is, the person is in extreme jeopardy and requires urgent intervention (Pagana and Pagana, 2010). Anemia is usually diagnosed in a man with a hemoglobin of less than 13 g/dL or in a woman with less than 12 g/dL. Levels of less than 13.3 and 12.6 respectively have been associated with a higher risk for death (Hardin, 2010; Zakai, et al., 2005).


The term hematocrit means “to separate blood.” It is the relative percentage of packed RBCs to the plasma in blood, after the two have been separated (often referred to as “spun down”). Although they measure different aspects of the RBCs, the hematocrit and hemoglobin are comparative numbers, with the hemoglobin approximately one third of the hematocrit. For example, a person with a hemoglobin level of 12 g/dL will have a hematocrit of approximately 36%. Critical values are less than 15% or more than 60% (Pagana and Pagana, 2010). Although the hematocrit is a marker of levels of anemia, it is not a good measure of overall blood volume. Elevations in hematocrit and hemoglobin may be the result of a pathological process but are more often an early sign of hypovolemia from malnutrition, dehydration, or severe diarrhea. The volume depletion must be corrected before an accurate interpretation can be done.



White Blood Cells


White blood cells (WBCs), or leukocytes, are divided primarily into two types—granulocytes (neutrophils, basophils, and eosinophils) and agranulocytes (monocytes and lymphocytes). They are found mainly in the interstitial fluid until they are needed and then travel to the site of invasion or infection. The number of WBCs is regulated largely by the endocrine system and by the need for a particular type of cell (Table 8-1). Each cell has a life span of 13 to 20 days, after which it is destroyed in the lymphatic system and excreted in feces. They are produced by the bone marrow and thymus and are stored in the lymph nodes, spleen, and tonsils. The average adult has 5000 to 10,000 WBCs/mm3. A major concern in the elderly is WBC elevations, often caused by bacteremia. A WBC count of less than 2500 or more than 30,000/mm3 is considered critical (Pagana and Pagana, 2010).



Bacteremia in the older population is a common cause for hospitalization, causing sepsis and septic shock and carrying a high mortality rate. In younger adults, the presence of infection or inflammation is commonly manifested as an elevated temperature, lymph node enlargement, and increase in total WBC count. However, in the older adult, these signs may be absent or not seen until the person is quite ill or septic. Rather than an increase in total lymphocytes, only immature neutrophils (bands) may be increased, called bandemia or a left shift. This lack of or delayed response reflects a diminished ability to respond to the intrusion of foreign substances, consistent with the immunity theory of aging (see Chapter 3). This change has significant implications for the gerontological nurse. Waiting for the “usual signs” of infection in an older adult may result in his or her death. Instead, the nurse must be alert for more subtle signs of illness such as new-onset or increased confusion, falling, or incontinence and respond to these changes earlier rather than later.


Exacerbating an already potentially dangerous situation is the frequency at which leukocytopenia is seen in older adults; it is caused by common medical conditions and commonly prescribed medications, for example, some antibiotics, anticonvulsants, antihistamines, analgesics, sulfonamides, and diuretics. On the other hand, increases in leukocytes may be a side effect of several drugs including allopurinol, aspirin, heparin, and steroids (Pagana and Pagana, 2010).


Neutrophils are produced in 7 to 14 days in the bone marrow and are in circulation for about 6 hours. They fight infections by phagocytizing bacteria. Neutrophilia, or increased neutrophils, may be an indicator of infections, connective tissue diseases such as rheumatoid arthritis, malignancies, use of medications such as corticosteroids, trauma, and metabolic conditions such as gout, uremia, thyrotoxicosis, and lactic acidosis (Pagana and Pagana, 2010). All are common conditions in late life.


Lymphocytes are divided into two types: T cells and B cells. T cells are produced by the thymus and are active in cell-mediated immunity; B cells are produced in the bone marrow and are involved in the production of antibodies (humoral immunity). In adulthood, 80% of lymphocytes are T cells, with a slight decrease in T cells and increase in B cells with aging. T-cell activity is especially important in late life, due in part to the naturally occurring immunosenescence (Chapter 3), especially depressed T-cell responses and T-cell–macrophage interactions (Auerhahn et al., 2007). Measurement of T cells is included in the monitoring of the health status and treatment response of persons infected with human immunodeficiency virus (HIV) or who have acquired immunodeficiency syndrome (AIDS). Together with neutrophils, lymphocytes make up 75% to 90% of all white blood cells (Pagana and Pagana, 2010).


Monocytes are the largest of the leukocytes. When matured they become macrophages and help defend the body against foreign substances, or what the body believes are foreign substances. The macrophages migrate to a site in the body where they can remove microorganisms, dead RBCs, and foreign debris through the physiological process of phagocytosis.


Eosinophils are involved in allergic reactions. They ingest antigen–antibody complexes induced by IgE-mediated reactions to attack allergens and parasites. High eosinophil counts are found in people with type I allergies such as hay fever and asthma. Eosinophils are involved in the mucosal immune response, which is known to diminish in late life (Freedman, 2009–2010a,b). Increased eosinophils in a peripheral blood smear may also be caused by infections such as tuberculosis or pulmonary fungal infections, rheumatoid arthritis, ulcerative colitis, regional enteritis, seasonal allergic rhinitis, atopic dermatitis, solid tumor cancers, and various lymphomas and leukemias (Pagana and Pagana, 2010).


Basophils transport histamine, a factor in immune and antiinflammatory responses, and heparin. Like eosinophils, they play a role in allergic reactions. They are not involved in bacterial or viral infections.



Platelets


Platelets are small, irregular particles known as thrombocytes, an essential ingredient in clotting. They are formed in the bone marrow, the lungs, and the spleen and are released when a blood vessel is injured. As they arrive at the site of injury, they become “sticky,” forming a plug at the site to stop the bleeding and to help trigger what is known as the clotting cascade (Thibodeau and Patton, 2003). Although the platelet count does not change with aging, the concentrations of a large number of coagulation enzymes increase (factors VII and VIII and fibrinogen). This and other developments indicate the possibility of hypercoagulability. However, at the same time, older adults are more likely to have blood diatheses resulting in unexplained bruising, nosebleeds, excess bleeding with surgery, and so on. If any of these signs are present, platelet counts and coagulation studies should be done. Counts of 150,000 to 400,000/mm3 are considered normal. Counts less than 100,000/mm3 are a cause for concern and considered thrombocytopenia; spontaneous hemorrhage may occur when the count falls below 20,000/mm3; at 40,000/mm3 spontaneous bleeding is uncommon but prolonged bleeding can occur with trauma or surgery (Auerhahn et al., 2007). Thrombocythemia indicates a platelet count greater than 1 million/mm3; bleeding still may occur due to abnormal functioning. The gerontological nurse caring for frail elders is expected to monitor patients for risk for bleeding, including understanding the meaning of their patients’ laboratory findings. For frail elders, such as those in long-term care facilities, thrombocytopenia can quickly lead to death should bleeding occur, such as from the gastrointestinal system or from a subdural hematoma occurring after a fall.



Common Diagnostic Testing


Measures of Inflammation


Erythrocyte Sedimentation Rate


The erythrocyte sedimentation rate (ESR), also referred to as the “sed rate,” is the rate at which an RBC falls to the bottom of saline solution or plasma in a set period of time. It is a proxy measure for the degree of inflammation, infection, necrosis, infarction, or advanced neoplasm. It may be slightly elevated (10 to 20 mm/h) in normal, healthy older adults, most likely due to the prevalence of chronic disease (Miller, 2009-2010). A more than minimal elevation indicates elevated serum proteins and inflammatory activity. The ESR is highly nonspecific and cannot be used for the diagnosis of any one disorder. However, it may be useful for monitoring several diseases and their treatments, especially inflammatory conditions such as polymyalgia rheumatica, temporal arteritis, or rheumatoid arthritis (Moore, 2006; Kreiner et al., 2010). If a person of any age has an unexplained rise in ESR, further assessment is indicated.



C-reactive Protein


C-reactive protein (CRP) is produced by the liver during the acute phase of inflammation or in the course of various diseases. Although originally used to determine cardiac events, it has been found a useful indicator for other forms of inflammation as well, such as after injury, surgery, or in the presence of infection. Tests of both CRP and ESR together are currently used, especially for the evaluation of an acute myocardial infarction (AMI). However, in a study of 5777 patients, Colombet and colleagues (2010) concluded that the joint measurement of ESR and CRP was not necessary; the ESR was misleading in a group of patients. The authors recommended that priority be given to the CRP measurement when inflammation is suspected. In another study of 163 persons, the CRP was found to be helpful in diagnosing septic joints, whereas the ESR was not (Ernst et al., 2010). The CRP was also found useful for predicting the risk for coronary heart disease among intermediate-risk subjects (Helfand et al., 2009). There is now a high-sensitivity assay for CRP (hs-CRP), which has increased the accuracy of the measurement even at low levels. While it too is variable and two measurements are needed, it still may be a stronger predictor of cardiovascular events than cholesterol (Pagana and Pagana, 2010).



Iron Studies


Anemia is the condition in which there is a reduced number of red blood cells and consequentially a reduced capacity for the transport of oxygen and carbon dioxide. Although not a normal change with aging, anemia is a common pathological finding in older adults, especially in the postoperative period and in those with long-standing chronic disease or renal insufficiency. In older adults the signs and symptoms are easily confused with other disorders, making diagnosis difficult or delayed. One of the first signs of anemia may be fatigue, which may be confused with a side effect of a medication or falsely attributed to normal aging. Progressive anemia that is untreated or not responsive to treatment will result in the person’s death. The advanced practice gerontological nurse must be able to diagnose and treat anemia. The gerontological nurse should be able to recognize the potential for anemia and to monitor its treatment.


Although a number of types of anemia exist, the most common in late life are anemia of chronic disease and inflammation, blood loss anemia, and that associated with protein-energy malnutrition. Diagnostic testing for anemia begins with what are referred to as “iron studies.” Iron studies include iron, ferritin, total iron-binding capacity (TIBC), and transferrin measures. Any of these alone is an inadequate measure because of the complexity of their interrelationships. In the presence of reduced hemoglobin, additional tests measuring folic acid and vitamin B12 may also be indicated.



Iron


The primary source of iron is through the consumption of iron-containing foods such as dark-green, leafy vegetables and red meats. The iron is transported by the plasma protein transferrin into bone marrow for storage and for use later in the production of hemoglobin. The serum concentration of iron is determined by a combination of its absorption and storage, as well as the breakdown and synthesis of hemoglobin. The iron in hemoglobin is necessary not only for the transportation of oxygen and carbon dioxide but also for controlling protein synthesis in the mitochondria, essential for generating energy in the cells (Freedman and Sutin, 2002). Serum iron (Fe) is reported as micrograms per deciliter (µg/dL). The TIBC measures the combination of the amount of iron and the amount of transferrin available in the blood serum. Ferritin is a complex molecule made up of ferric hydroxide and a protein, and its measurement reflects body iron stores.


Adequate stores of iron are necessary to maintain health. The body is then able to respond quickly to the demand for increased oxygen and energy and to replenish iron lost through bleeding.



Vitamins


Mild vitamin deficiencies are common in later life and should be considered any time there is cognitive impairment, delayed wound healing, or anemia. Those at highest risk are persons who may have protein-calorie malnutrition. Short-term undernutrition is associated with B and C vitamin deficiencies. For those with longer durations, the deficiencies may also include A, E, B12, and K (Johnson, 2009-2010). Vitamin D deficiencies are now being found in both apparently healthy and ill adults. Because of the higher risk for and more serious effects from vitamin deficiencies, general supplementation is often recommended.



B Vitamins


The two B vitamins that are especially important to hematological health are folic acid and B12, two of the eight B vitamins in the B-complex. Folic acid is formed by bacteria in the intestines; it is necessary for the normal functioning of both RBCs and WBCs, and for deoxyribonucleic acid (DNA) synthesis (Nicoll et al., 2004). It is stored in the liver and can be found in eggs, milk, leafy vegetables, yeast, liver, and fruit. Decreases in folic acid may indicate protein-energy malnutrition, several types of anemia, and liver and renal disease. It is more common among persons with chronic alcohol abuse. Although folic acid levels do not decrease in healthy aging, the nurse must be alert for signs of actual or potential nutritional deficits. Folic acid is usually measured in conjunction with that of vitamin B12 levels.


Vitamin B12 (cyanocobalamin) is a water-soluble vitamin required for the normal development of RBCs, neurological function, and DNA synthesis. If untreated, vitamin B12 deficiency is ultimately fatal. Vitamin B12 is found in products such as eggs, fish, shellfish, and meat, half of which may be bioavailable. It is first extracted from food by gastric acid and pepsin in the stomach. In the intestine B12 binds with intrinsic factor for absorption and entry into the circulation. Vitamin B12 deficiencies resulting in megaloblastic (pernicious) anemia have been attributed solely to lack of intrinsic factor (Box 8-1). More recently a milder form of B12 deficiency has been identified and may be caused by normal and common age-related changes in the stomach wherein B12 is not released from food. This type may apply to 60% to 70% of the cases of vitamin B12 deficiency in later life (Cadogan, 2010).



BOX 8-1


Laboratory Testing and Vitamin B12




Adapted from Cadogan MP: Functional implications of vitamin B12 deficiency, Journal of Gerontological Nursing 36:16, 2010.


Clinical manifestations of B12 deficiencies include elevated homocysteine levels, glossitis, increased lactate dehydrogenase (LDH) levels, paresthesias of the feet and hands, and vibratory and proprioception disturbances. Ataxias will also occur without treatment. Cerebral manifestations include memory impairment, change in taste and smell, irritability, and somnolence. Tests of B12 and folate are now part of the standard workup for dementia (Sink and Yaffee, 2004).Testing for a B12 deficiency is indicated when there is unexplained neurological or functional decline.



Vitamin D


Vitamin D deficiencies have been found to be common. Aging skin combined with decreased exposure to sunlight result in a reduction of the conversion of 7-dehydrocholesterol to vitamin D3 (cholecalciferol) by ultraviolet light. In turn, the vitamin D deficiency reduces the absorption of calcium into bone. It has been demonstrated that in response to the lowered levels of calcium, the secretion of parathyroid hormone increases, triggering increased bone resorption. Ensuring adequate intake of calcium and vitamin D is essential for healthy aging.


Vitamin D levels are measured in the blood, using 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 to determine total 25-hydroxyvitamin D levels. A level of 20 ng/mL indicates a deficiency, 20 to 30 ng/mL an insufficiency, and greater than 30 ng/mL a sufficiency (optimal). There is a considerable amount of research currently underway examining the effect and implications of the wide scale deficiencies of Vitamin D that have been observed (Planton, Meyer, Eolund, 2011).



Blood Chemistry Studies


Blood chemistry studies include an assortment of laboratory tests that are used to identify and measure circulating elements and particles in the plasma and blood: glucose, proteins, amino acids, nutritive materials, excretion products, hormones, enzymes, vitamins, and minerals. Some of these are used for screening and others for monitoring specific health problems or treatments. Some tests are individually selected, but many are done in “panels” or grouped in clusters with a variety of names, including “Chem-7” or “BMP” (basic metabolic panel) or “SMA-16” or “CMP” (complete metabolic panel), among others. The nurse must become familiar with the names and test components used by the laboratory that provides services to her or his patients (Box 8-2).



BOX 8-2   Effects of Aging on Laboratory Values





Hormones: Thyroxin


In the older man and postmenopausal woman, the hormones that receive the most attention are those related to the thyroid gland: triiodothyronine (T3), thyroxine (T4), and thyroid-stimulating hormone (TSH). Although changes in thyroid function are not a normal part of aging, the incidence of disturbances, especially hypothyroidism, is seen with increasing frequency. However, some of the deviations are the result of other, nonthyroid conditions. Screening for thyroid disease is a component of the primary health care of older adults, especially women and persons with depression, anxiety, dementia, or cardiac arrhythmias. A fully functioning thyroid gland (or its replacement) is necessary to maintain life. TSH is produced by the pituitary to stimulate the thyroid to produce T3, which in turn is converted to T4.


Although all of the previously mentioned hormones are commonly included in a thyroid panel, the serum free T4 and TSH levels are the most important for the initial diagnosis. If the person has a goiter, a thyroid scan with technetium may be necessary (Brashers and Jones, 2010). In most cases, treatment (especially thyroid replacement) can be monitored easily on the basis of TSH alone.


Hypothyroidism is the most common disturbance seen in older adults, affecting only 1% of the younger population and 5% of those over 60 (Fitzgerald, 2010) (see Chapter 15). The most common causes are autoimmune thyroiditis, prior radioiodine treatment, and subtotal thyroidectomy. Hypothyroidism can also be iatrogenic, from provider-prescribed thyroid replacement that is not adequately monitored. Hypothyroidism is diagnosed by the clinical picture combined with laboratory findings, especially markedly elevated TSH and reduced total and free T4 (Table 8-2). However, the accuracy of the laboratory findings is easily affected by concurrent environmental conditions and drug intake, making an accurate diagnosis somewhat difficult (Table 8-3).


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Nov 6, 2016 | Posted by in NURSING | Comments Off on Laboratory Values and Diagnostics

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