hs-CRP: Inflammation You Can Measure

C reactive protein is made by the liver whenever there is inflammation somewhere in the body. The high sensitivity version of the test, hs-CRP, reads the low end of the scale accurately, down to fractions of a milligram per liter, which is where the information about heart risk lives. A standard CRP is built to catch an infection or a flare of arthritis. The high sensitivity one is built to catch a smolder.

What it tracks

Atherosclerosis is partly an inflammatory process. Cholesterol particles lodge in the artery wall, immune cells arrive, and the wall stays mildly irritated for years. hs-CRP is a rough readout of how much of that low grade inflammation is going on across the whole body, not just the arteries.

The cutoffs most labs and guidelines use are simple. Under 1 mg/L is low risk. Between 1 and 3 is average. Over 3 is high. People in the high group have had roughly double the heart attack and stroke rate of people in the low group in large populations, even after accounting for cholesterol. That is why we add it to a cardiovascular workup alongside ApoB and Lp(a). ApoB counts the particles; hs-CRP gives a rough read on the background inflammation those particles are meeting.

We aim for under 0.5 mg/L.

Excess body fat, especially around the organs, is one of the most common reasons it sits above 3. Poor sleep, smoking, gum disease and insulin resistance push it up too. Losing visceral fat, training regularly and sleeping well bring it down, and the drop is often visible within months.

Why one draw can mislead

CRP responds to anything. A cold the week before, a hard race two days earlier, a sprained ankle, a dental infection, even a heavy strength session can lift it several fold for a few days. Picture a hypothetical 40 year old who runs a half marathon on Saturday and has labs drawn Monday. Her hs-CRP comes back at 8. Three weeks later, rested, it is 0.4. Neither number was wrong. One of them was just not about her arteries.

So we never act on a single high value. If hs-CRP comes back elevated, we ask about the previous two weeks, then repeat it at least two weeks later, rested and well. Two readings in the same range are a pattern. One is a snapshot.

What we do with it

A persistently high hs-CRP in someone whose ApoB is also high moves us to treat the cholesterol more aggressively and to look harder at body fat and sleep. A high value with a clean lipid panel sends us looking for the source: weight, a gut problem, an autoimmune process, a joint. A low value is reassuring but does not clear you on its own; plenty of people have had heart attacks with an hs-CRP under 1.

It is an inexpensive test, and most routine checkups never include it. That's why we check it.

This article is educational and is not medical advice.

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