The traditional CRP test uses immunoassay methods that are sensitive to concentrations of 5-20 mg/L. The hs-CRP test, with its increased sensitivity, is able to detect C-reactive protein in lower levels, 0.5-10.0 mg/L. As with most risk markers, the results of hs-CRP testing are generally interpreted on a relative scale; the higher the value, the higher the risk of a future cardiovascular event.
The American Heart Association and Centers for Disease Control and Prevention has defined risk groups with hs-CRP as follows:
- Low risk: < 1.0 mg/L
- Average risk: 1.0 to 3.0 mg/L
- High risk: > 3.0 mg/L
It is important to note that hs-CRP assays are measuring the same protein as traditional CRP assays. Thus, in patients with active inflammation (such as chronic, active arthritis; lupus; infection; etc.) hs-CRP values would be expected to be high and would not necessarily implicate cardiovascular risk. If values greater than 10 mg/L are seen in repeated measurements, a non-cardiovascular cause should be considered. Taking anti-inflammatory drugs (NSAIDs, aspirin, etc.) or the statin-class of cholesterol-lowering drugs may reduce CRP levels in patients. This is not an artifact, but is thought to be an effect of treating the underlying inflammatory process.
