What Your Doctor Doesn't Tell You About LDL Measurements

American standards of medical practice dictate that almost every diabetic will eventually be placed on a cholesterol-lowering statin drug, as soon as blood tests come back with an LDL number over 100 mg/dl two times in a row. But most diabetics, and many doctors, don't realize that standard blood tests don't even measure LDL, they estimate it.

While the numbers diabetics get with the lab reports tell them total cholesterol, HDL, and triglycerides, the LDL number is a guestimate. That's because low-density lipoprotein (LDL) is lighter, bulkier, and harder to measure directly, so labs make a quick and dirty approximation as follows:

Total cholesterol - HDL - 1/5 of triglycerides = Estimated LDL.

We tend to think of cholesterol as either HDL ("good") or LDL ("bad"), but there is also another form of cholesterol, VLDL, or very low density lipoprotein. Cholesterol is actually an essential substance, not a poison. Every cell in the body is lined, in part, with polymers made with cholesterol. Brain tissue requires enormous amounts of cholesterol. Cholesterol protects the "insides" of cells from oxidating chemicals "outside."

Most of the body's cholesterol is made in the liver. Only about 15 per cent, typically comes from food. Larger, lighter particles of cholesterol are progressively stripped down and used, VLDL to LDL to HDL, but only the LDL can become oxidized and trapped in the linings of blood vessels. And not all the LDL poses an atherosclerosis risk. The form known as apo-B can form plaques. Apo-A does not.

But how does this explain why diabetics are so often prescribed statins for cholesterol?

Let's say you take your diagnosis of diabetes seriously, and you work hard to get your sugars down. You diet, you exercise, you take medication. You lower your blood sugars and your body has less excess glucose to turn into triglycerides.

Now let's take another look at that equation:

Total cholesterol - HDL - 1/5 of triglycerides = Estimated LDL.

If you lower your triglycerides, you raise your estimated LDL.

That would be fine if VLDL always equalled 1/5 of triglycerides, but it doesn't. As you get better and better control over your diabetes, your LDL estimates are going to appear to go up, whether there's more LDL in your bloodstream or not. Many diabetics are prescribed statin drugs they don't need because it's easier to write a prescription than to run another blood test.

Be forewarned that direct measurement of your LDL can cost more than all the other blood tests for your diabetes exam put together. If the test comes back that you do not really need a statin, however, the blood test pays for itself in about four months--and you will not be needlessly exposed to any side-effects of statin drugs. Even better, a doctor who takes the trouble to measure your actual LDL is far more likely to respect all the effort it takes for you to control your blood sugars.