Secondary factors, such as early disease stage, alter laboratory findings for the elderly

Laboratory values for aging Americans should be compared against those of younger adults

Orlando, FL – Something curious has been happening in clinical laboratories. The findings for the elderly have differed creating a new benchmark of acceptable status of health. Yet accommodations for aging may be detrimental, even dangerous, in efforts to assess the health status of those growing older.

For years, those who conduct research to better the human condition have noted that some laboratory test results vary as a person ages. How do these variations affect the patient? Are these variations tied only to the age of the patient, or are there secondary factors? And how significant are these secondary factors?

Joseph Knight, MD. Professor of Pathology and head of the Division of Education, Department of Pathology at the University of Utah., and author of the book, Laboratory Medicine and the Aging Process (ASCP Press) has identified four major problems in interpreting laboratory data derived from elderly patients:

Multiple disorders/diseases are common;
Subclinical diseases/disorders (early stage without symptoms) are common.
Many elderly take multiple drugs.
Poor nutrition is a common problem.

All these secondary factors are important to Dr. Knight’s assertion that aging and disease are not the same. Aging predisposes one to various diseases; for example, of the ten major causes of death in the United States, some 65-70 percent are lifestyle related (primarily obesity, physical inactivity, poor nutrition, smoking, and excessive alcohol intake).

Dr. Knight will present "Selected Topics in Laboratory Medicine and Aging," at the 54th Annual Meeting of the American Association for Clinical Chemistry (AACC). AACC (http://www.aacc.org/) is the scientific organization for clinical laboratory professionals, physicians, and research scientists. Their primary commitment is the understanding of laboratory testing to identify, monitor and treat human disease. More than 14,000 attendees are expected for the meeting, which is being held at the Orange County Convention Center, Orlando, FL, July 28-August 1, 2002.

His presentation will address the ideal reference values for so-called "healthy" elderly. Reference values are laboratory test values obtained from an individual or group (in this case, the elderly) in a defined state of health. This term replaces normal values, since it is based on a defined state of health rather than on apparent health.

Dr. Knight suggests that present laboratory values assigned to elderly to assess a state of health at a level associated with aging but later proved to be subclinical. Values measured include levels of cholesterol, thyroid-stimulating hormone, sodium, potassium, magnesium, selenium, zinc, albumin, blood urea nitrogen, and creatine, all important to the body’s key processes.

By adjusting reference values to those of a younger, healthier individual, Dr. Knight reviewed the literature of research and found that secondary factors in the laboratory resulted in:

A missed diagnosis of hypokalemia (the presence of an abnormally small concentration of potassium ions in the circulating blood; occurs in familial periodic paralysis and in potassium depletion due to excessive loss from the gastrointestinal tract or kidney) and hypomagnesemia, subnormal blood serum concentration of magnesium.
Zinc deficiencies, which are found in those relying on diuretics or having cirrhosis, diabeties, or oor nutrition. Lack of this element can lead to anorexia, impotence, or poor wound healing.
Mean zinc reference levels found in plasma for the elderly are 10.5 umo/L and 12.7 in healthy young adults.
Selenium, a trace element found in two major enzymes, is found at lower levels in the elderly. Previous studies have revealed a reduced incidence of experimentally produced cancers in animals when a selenium supplement is introduced. Low levels also adversely affect the immune system.
TSH elevation leading to hypothyroidism, particularly in women 35 years and older.
Hypocholesterolemia (presence of abnormally small amounts of cholesterol in the circulating blood), occurs in various acute and chronic illnesses. Several studies found a relationship between low serum cholesterol levels and increased risk of premature death.

Accordingly, disease, not evident by symptoms, is affecting the values accorded to the benchmark of mislabeled "healthy" elderly individuals. Dr. Knight recommends that ideal reference values for the elderly should be those found in young, health adults, where subclinical disease is not present. Doing so would assist in eliminating the elderly’s misplaced complacency about their health and possibly spur needed changes in lifestyle and screening programs.

Editor’s Note: To interview Dr. Knight, please contact Donna Krupa at 703.527.7357 (direct dial), 703.967.2751 (cell) or djkrupa1@aol.com. Or contact the AACC Newsroom at: 407.685.4215.

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