Population norms, but not individual norms, can be established for any physiologic parameter and its laboratory measurement. Yet, variability is the hallmark of aging, and physiologic change is no exception; as a result, extrapolating from norms to individuals is done with less confidence in the elderly. Many normal elderly persons show little or no physiologic decline in organ function, while many others show significant decline. One of the most useful techniques to establish the presence of disease is to compare current laboratory values with results obtained when disease was not present. Of course, this type of comparison is likely to be possible only for routinely performed tests.
Age-associated declines in cardiac, pulmonary, renal, and metabolic function correlate with changes in normal laboratory values (see TABLE 113-2). For example, systolic blood pressure increases, and maximal cardiac output decreases whether measured invasively or noninva-sively. Vital capacity, forced expiratory volume at 1 sec, and maximal breathing capacity decrease progressively with age

Deviations in results (which, in many cases, were more likely the result of disease than of normal aging) were noted in 5% to 10% of the population for the following: women > 80 yr, a low hematocrit; women 65 to 80 yr, elevated calcium levels; both sexes of both age groups, reduced serum phosphate concentrations and elevated lactic dehydrogenase (LDH) and alkaline phosphatase levels.
Serum electrolyte values are not abnormal because of age alone. Alkaline phosphatase values approaching 140 u./L may be found in up to 5% of persons of all ages (normal = 35 to 120 u./L), but elevations may be caused by some drugs (eg, narcotics), eating a fatty meal, and bone abnormalities (including tumors, hyperparathyroidism, Paget’s disease, a healing bone fracture, osteomalacia, and renal osteodystrophy). However, the positive predictive value of an elevated alkaline phosphatase level is very low in patients with no prior diagnosis of liver disease, malignancy, or bone disease.
In patients with osteoporosis, levels of serum calcium, phosphate, and alkaline phosphatase and the electrophoretic protein pattern are usually normal. In patients with metastatic cancer and almost always in those with osteomalacia, alkaline phosphatase is increased. Transient increases that do not usually exceed normal limits are noted in osteoporotic women after hip fractures.
A low serum albumin level in a healthy person is usually dietary in origin and unrelated to aging. However, serum albumin tends to fall when older persons develop serious disease, especially when accompanied by undernutrition. Vitamin deficiency, except for B12, is rare in healthy ambulatory persons; studies have reported vitamin B12 deficiency in 12% of hospitalized elderly patients who have no evidence of general malnutrition.
Serum ferritin increases with age, and serum iron decreases minimally. Although fasting blood glucose increases with age, values remain within the normal range. Glucose tolerance decreases gradually with age. However, lack of exercise, obesity, and the use of some medications may be more important influences on glucose tolerance than age alone. Glucose levels are highest in the nonfasting state after a carbohydrate challenge or during a cortisone-glucose tolerance test. HDL cholesterol level tends to rise with age, as does LDL cholesterol, but this is based on values in survivors and, therefore, may not be a general aging trend.

Prostate-specific antigen (PSA) levels rise with age; the levels are typically about 2.5 ng/mL in men 40 to 49 yr of age, increasing to about 6.5 ng/mL by age 70 to 79. PSA levels may increase as a result of conditions other than cancer, such as benign prostatic hyperplasia or a prostatic infection, or briefly as a result of prostatic manipulation.
Age per se has no influence on the erythrocyte sedimentation rate (ESR). The sensitivity of an ESR > 20 mm/h in identifying the presence of a clinical disorder is 0.55; however, the specificity is 0.96, and the positive predictive value of an elevated ESR being associated with a clinical disorder is 0.93. Monoclonal gammopathy or elevated fibrinogen level, as well as more common chronic inflammatory diseases, can be a cause of elevated ESR in patients having no other obvious cause. The influence of plasma fibrinogen, total protein, serum globulins, and immunoglobulins on the ESR in older persons is similar to that in younger adults. Therefore, any age-related changes in ESR are best explained by disease rather than by aging itself. Severe anemia or hypo-albuminemia limits the test’s usefulness.
A study using agarose gel electrophoresis and immunofixation demonstrated a 10% incidence of monoclonal gammopathy in apparently healthy persons ranging in age from 62 to 95 yr. The incidence is 6% in persons < 80 yr and 14% to 19% in those > 90 yr. An unexplained ESR elevation in the elderly warrants investigation for a monoclonal gammopathy, which occurs in about 35% of such persons. These gammopa-thies may indicate a dysregulation of the immune system occurring with age (ie, impaired T-cell or B-cell function).
Serum levels of the major subsets of immunoglobulins (IgG, IgM, and IgA) do not show clinically significant changes with age. A decline in several T-cell functions is the most consistent age-related change in the immune system.