When to worry about blood test results? Abnormal readings aren’t always a problem !

Blood tests are an indispensable tool of medicine. They’re used to screen, diagnose, confirm, and monitor diseases. There are many hundreds of them, and each one is subject not only to observation but also to interpretation.

There is no such thing as a perfect lab test, but all tests done by accredited labs today use methods that have been scrutinized and approved by National Accreditation Board for Testing and Calibration Laboratories (NABL). And the government certifies and inspects these labs regularly to make sure they’re keeping up standards.

Those “reference ranges” you see on the reports may vary slightly from lab to lab, depending on which of several possible methods a lab chooses to use. Test results can also fall outside the reference range for reasons that have nothing to do with disease or medications.

One common example: ­Patients who follow the usual instruction to have “nothing to eat or drink the night before” can end up with high blood urea nitrogen, which assesses kidney function. Their kidneys are fine, but they’ve dehydrated themselves enough to cause an elevated reading. That’s why we tell our patients to have “nothing to eat or drink from dinner the night before—except for liberal amounts of water.” As a bonus, adequate hydration makes it easier to draw blood by plumping up the veins.

And triglycerides and blood glucose levels, included in many routine blood tests, are very sensitive to the time of the last meal and reach the “fasting” baseline only after 8 to 12 hours without eating. So patients who had that late-night snack and have their blood drawn early the next morning might have out-of-range ­results.

Other abnormal readings may or may not indicate a problem. A high lev­el of creatine phosphokinase, a muscle enzyme, can signal a heart or muscular ailment—or it can mean you worked out shortly before your blood was drawn.

And if you’re an adolescent or recovering from a broken bone, a high level of alkaline phosphatase, a bone (and liver) enzyme, is completely expected; but if you’re not, it could be an ominous sign of liver disease or certain cancers.

So even if you exercise your option to receive your results directly from the lab, you should still get your doctor to weigh in and not try to decode the data yourself.