It’s All in the Blood
In the body, blood knows all.
It touches the deepest recesses and farthest reaches of the body. Blood is intimately familiar with each cell, its health or sickness, its needs and wastes.
No wonder, then, that as part of a routine physical exam your physician generally draws a vial or two of blood and sends it off to a laboratory for testing.
What comes back, though, isn’t quite so poetic. Ask for a copy of the lab results (and you do have to ask; generally they just go directly to the physician) and what you’ll see is a jumble of letters and numbers. You might note that your HGB is 11.8, a little low; or that your LDH is 440, right on target.
Blood screening usually covers 30 or 40 tests, each with its result and its “reference range,” not to mention footnotes and alarming notations like “high” and “slight.”
“These tests are intended as an adjunct to the clinical evaluation of patients, not as diagnostic measures on their own,” says Dr. Neville Colman, director of the department of pathology and laboratory medicine at St. Luke’s-Roosevelt Hospital Center in New York City.
Part of the problem with blood screening is that the reference range--the range of results often understood as “normal” readings--encompasses 95% of the health populations. But for any test, the results for those other 5% of normal, healthy people will fall outside that range.
“If you see a result on yourself and you’re outside that range, your concern is that something’s wrong. Whereas it might just mean that you’re in the 5% of the population that’s outside that range,” says Dr. Michael B. Bongiovanni, director of the clinical laboratory at Hershey Medical Center of Pennsylvania State University. “And given the number of tests performed, there’s almost a two-thirds chance that you’ll lie outside the norm on at least one test” without indicating any problem.
Compounding the challenge is the possibility of mistakes in the laboratory--labs analyze thousands upon thousands of samples daily--and errors in how the sample was taken.
So how can one distinguish between an “abnormal” reading that means nothing and one that signals trouble? Look it over with the physician who ordered the screening. In large measure, what you’re paying a doctor for is information; if your doctor is unwilling to provide it, maybe you need a different doctor.
There are five areas of blood test results that provide a good overall indicator of your health. They are:
* Red blood cell count (RBC), hemoglobin (HGB) and hematocrit: All are measures of hemoglobin, the oxygen-carrying component of red blood cells. A low reading signifies some degree of anemia. Among the possible causes are an iron-deficient diet, slow internal bleeding as from a gastric ulcer, and in women, the menstrual cycle. Pregnant women tend to have low hemoglobin levels, but this doesn’t necessarily indicate a problem.
* Glucose: A greatly elevated level strongly suggests diabetes. Blood glucose increases following a meal, so your physician may suggest fasting before the blood is drawn to control for this factor.
* Blood urea nitrogen (BUN): A measure of how well the kidneys are working. Creatinine is a similar indicator.
* Transaminase (AST, ALT), bilirubin, alkaline phosphatase: This measures liver functioning. May be elevated if you had a few drinks the night before.
* Cholesterol: An indicator of your risk of developing heart disease, the No. 1 killer of Americans. It’s reported as LDL (“bad”) and HDL (“good”) cholesterol levels; a total cholesterol count under 200 milligrams per deciliter is considered good, but perhaps more important is the ration of LDL to HDL cholesterol. For men, that ratio averages 3.55; for women, 3.22. The lower the number, the lower your risk.
Finally, a mention of the most discussed blood test of the past five years: PSA, or prostate specific antigen, a screening for the antibodies associated with prostate cancer. This test is routinely performed on men older than 50, or older than 40 with a family history of prostate cancer or who are African American. One problem has been that PSA levels can be elevated by a benign enlargement of the prostate gland; a new blood test being developed is said to be more accurate at pinpointing antigens that result only from cancer.
