Ask the doctor

What causes C-reactive protein levels to vary?

Q. Last year I had a high-sensitivity C-reactive protein test (hsCRP) that came back at 38.6, which my doctor said was quite high. My cholesterol levels were fine; a subsequent heart scan and stress test were both normal. When my doctor repeated the test, my hsCRP level was 6.1. What can cause such big variations in this test? I have a thyroid condition, but nothing other than that.

A. A value of 38.6 for hsCRP is not unheard of, and there are some people who have levels in this range because of their genes. As a rule of thumb, when the value of an hsCRP test is above 10 milligrams per liter (mg/L), it is best to repeat it in two to four weeks to make sure it wasn't picking up an unrelated infection. Your doctor did the right thing by repeating your test.