By HANS DUVEFELT, MD
Many patients make this or similar requests, especially in January it seems.
This phenomenon has its roots in two things. The first is the common misconception that random blood test abnormalities are more likely early warning signs of disease than statistical or biochemical aberrances and false alarms. The other is the perverse policy of many insurance companies to cover physicals and screening tests with zero copay but to apply deductibles and copays for people who need tests or services because they are sick.
It is crazy to financially penalize a person with chest pain for going to the emergency room and having it end up being acid reflux and not a heart attack while at the same time providing free blood counts, chemistry profiles and lipid tests every year for people without health problems or previous laboratory abnormalities.
A lot of people don’t know or remember that what we call normal is the range that 95% of healthy people fall within, and that goes for thyroid or blood sugar values, white blood cell counts, height and weight – anything you can measure. If a number falls outside the “normal” range you need to see if other parameters hint at the same possible diagnosis, because 5% of perfectly healthy people will have an abnormal result for any given test we order. So on a 20 item blood panel, you can pretty much expect to have one abnormal result even if you are perfectly healthy.
One way I explain this to my patients is that if you say that every person under a certain height is a dwarf, you will misdiagnose many people. You need to look at, in this case, other parameters such as head size, length of the fingers and so on. An isolated number doesn’t mean very much.
In some cases normal or abnormal values do not represent health versus disease. For example, a fasting blood sugar of 120 mg/dL is considered non-diabetic in the United States but a diabetic level in Canada. You have to draw the line somewhere and where you draw it is a judgment call or a matter of consensus. For example, we are not entirely clear on the clinical significance of a slightly low vitamin D level, which is being studied and debated right now. And in the case of magnesium, you can have a normal level in the blood and be severely deficient in the rest of your body because we are designed to maintain a certain blood level more or less at all cost. Serum sodium doesn’t correlate completely with the level in our cerebrospinal fluid and brain, so it is possible that of two people with low sodium levels, one can be healthy and the other one desperately ill.
On top of all the vagaries of test interpretation, can anybody imagine how many things we can now test for, how much that can cost and what insurance company would consider footing the bill for such blanket requests?
So I try to not order any bloodwork before annual physicals. I want to know what’s going on, what my patient’s priorities are and make a shared, informed decision about what to test for. I can still use the physical exam diagnosis code to get many tests that patients want covered, but it would be preposterous and presumptuous for me to order hepatitis C, HIV or urine chlamydia and gonorrhea tests without asking patients if they want to be tested.
Hans Duvefelt is a Swedish-born rural Family Physician in Maine. This post originally appeared on his blog, A Country Doctor Writes, here.
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