The End of Fasting Labs

But first, let’s ask a bigger question. Is the whole process of annual physicals and blood tests of any merit, or is this just another money making scam foisted on the American public by physicians looking to fill their appointment slots? It is not uncommon to find some concierge doctors ordering all sorts of unproven diagnostic tests of minimal value just to make patients happy. Here at MedNorthwest, I really push back on that approach. Still, shouldn’t we exercise that same degree of skepticism, even in the concierge medicine setting, when it comes to routine annual exams and labs?

Well, the annual exam probably does have some merit. First, if you’re on a long-term medication like Lipitor or Prozac, then there are certain legal requirements that we have an actual physician-patient relationship, and the requirement can be met by seeing you once per year at least. But for patients on no medications at all, even the most curmudgeonly and stingy of health care experts would agree that screening for high blood pressure, giving flu shots and other needed immunizations, checking to see if patients are depressed, helping folks quit smoking, and screening for diabetes all have value. The interested reader is referred to the 339 page document out of Johns Hopkins titled “Value of the Periodic Health Evaluation,” which is also an effective treatment for insomnia.

Labs. Fasting or Not?

The role of extensive annual blood work, however, is more controversial. In our practice, since we’re going to be drawing blood anyway to screen for some very basic things such as anemia and diabetes, we do run about 50 different tests, looking at the function of the kidneys, liver, thyroid, bone marrow, and screening for abnormal cholesterol and several other medical problems. (Screening for vitamin D deficiency might make sense in a place like Seattle, but insurance often refuses to pay for it.) The purist would argue that we run too many tests but honestly, the incremental cost is very small and the risk to the patient in the hands of a reasonably skilled clinician interpreting the results is low.

But what about the whole fasting angle? Well, in the fasted state, we get a more reliable look at blood sugar, which is the main way we screen for diabetes. Also, triglycerides go up after eating and trying to check patients for an elevation in the triglyceride level is much easier if patients are fasting. If patients fast year after year, we have a reproducible baseline with which to compare results, and also, fasting year after year results in a lot of weight loss!

So what, then, is the problem with fasting? Well, for one, patients get hungry. Requiring fasting labs puts in a slight disincentive for individuals to come to the office for their annual exam. Another issue is convenience. If you have to be fasting, most folks would realistically only be able to get labs drawn at 9:00 or 10:00 AM, which does not necessarily fit everyone’s schedule.

The Argument Against Fasting

There are also clinical and scientific arguments against fasting. It turns out that total cholesterol, HDL (good) and LDL (bad) are not really affected much by being in the non-fasted state. In one study, eating lowered the LDL cholesterol by about 7 points at the absolute most. It might seem counter-intuitive that total cholesterol, HDL, and LDL all fall slightly after eating, but this is what the research shows. It turns out that the variation between fasting and not fasting cholesterol is less than the typical lab-to-lab variation in these values. If you send your blood to two different labs simultaneously, you can easily see a 5% difference in cholesterol values. Only triglycerides go up substantially in the non-fasted state, but even here, there is a nice study showing that non-fasting triglycerides are a better predictor of cardiovascular risk than fasting triglycerides. If you read the National Cholesterol Education Project (NCEP) guidelines for high cholesterol screening and treatment (and these only run to 284 pages), you’ll see that fasting labs are recommended. But one reason is that their approach to measuring LDL (bad) cholesterol is to calculate it from a simple math formula based on the other cholesterol measures. It is called the Friedewald equation, and named after Dr. William T Friedewald. In the old days, measuring LDL (bad) cholesterol was a very complex, expensive lab test and Dr. Friedewald, who went to medical school at Yale and probably had a lot of school loans, published it in 1972 as a cost saving measure. But hey, Dr. Friedewald, the seventies called and they want their formula back, because in our lab we measure LDL cholesterol directly and don’t depend on your equation. This makes our determination of LDL more accurate in the non-fasted state.

This is a good opportunity for me to remind patients that risk factor modification is the most important approach to reducing your chance of a heart attack. So of course, quitting smoking, eating well, and getting exercise are very important. However, the biggest risk factors are not cholesterol, but advancing age and male sex. These are a little harder to modify, but traveling in space close to the speed of light will make you age more slowly than the rest of us.

The Diabetes Question

But what about blood sugar? Everybody knows that your blood sugar rises after a meal and falls when you have not eaten. The standard for diagnosing diabetes involves a fasting blood sugar over 125. Still, any non-fasting sugar over 200 on a couple of occasions also makes the diagnosis. More importantly, we screen for diabetes with an additional test, the hemoglobin A1c, sometimes abbreviated as HgbA1c. This test measures the average blood sugar over the preceding two to three months. Patients often wonder how this is possible. How can a blood test in June tell what a patient’s blood sugar was doing in April and May? Well the answer is that inside each red blood cell is a little man with a clipboard and he keeps track of what you eat and writes down your blood sugar that day on a list.

The hemoglobin inside the red cells

is bathed in your blood

as the cells circulate around the body.

Actually the way it works is that your red blood cells have a lifespan of about four months. The hemoglobin inside the red cells is bathed in your blood as the cells circulate around the body. If hemoglobin is bathed in a high glucose bath, then more glucose molecules end up sticking to the hemoglobin, kind of the way barnacles stick to a dock. The test measures the percentage of glucose stuck to hemoglobin molecules. Normal is 5.6% or lower, and 6.5% or higher is diabetes. Between the two is pre-diabetes. Since blood cells are recycled every 120 days, you get a mix of newer cells with very little sugar stuck to their hemoglobin and older cells ready to be killed off and eaten up by the spleen that are chock full of sugar. The test takes the overall average. A high percentage indicates high sugar, both fasting and non-fasting, and this is diabetes. One can see that this test does not require fasting on any particular day. Of note, the normal range for a hemoglobin A1c has changed, with lower, stricter limits set in 2010. You could have had normal blood sugar in 2009 and been pre-diabetic in 2010 with the same lab values.

Other Tests

Having dispensed with cholesterol and blood sugar, there still are about 48 other tests in the annual blood panel. We screen for thyroid and liver disease, kidney failure, abnormalities in body chemistry involving calcium, sodium, and potassium, blood and bone marrow diseases including anemia and leukemia, and other issues as well. None of these tests are substantially affected by fasting. In specific cases, we add additional tests that are also not affected by fasting.

In Conclusion

My recommendation for MedNorthwest patients is that fasting labs are optional. Sure, there may be the occasional person where fasting lab tests are required, and rarely we might end up repeating labs in the fasted state for certain reasons. But for about 95% of our practice, the convenience and flexibility of doing annual labs in the non-fasting state outweighs any tiny, often theoretical benefit from fasting labs. In addition, patients can come to our office in Seattle for labs, but we have blood drawing sites we can use throughout the state if that is more convenient. By removing one more barrier to care, we are likely to see better overall treatment and outcomes for our patients. Sure, it’s concierge medicine, but just because a patient can easily get in to see a concierge doctor for an annual exam and labs doesn’t mean that person wants to come in. It’s apparent that since instituting this policy, we’ve definitely reduced the number of stragglers who don’t want to come in for their annuals.