Harvard Heart Letter

Ask the doctor: What causes C-reactive protein levels to vary?

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.

However, your repeat value of 6.1 mg/L is still well above the threshold of 3.0 mg/L that suggests an increased risk for cardiovascular disease from inflammation.

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