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Use of hs-CRP, Measurement, and Ranges

In 2002, the AHA and CDC recommended measurement of hsCRP as an aid in the diagnosis and treatment of CVD. There is debate surrounding the use of hsCRP. Most large laboratories offer assays for CRP and hsCRP because demand for these tests was once quite high. More recently however the value of hsCRP has been questioned. There are large studies showing that hsCRP is in fact elevated in patients who have real cardiovascular risk. However these studies are population studies comparing large groups with high hsCRP to large groups of people with low hsCRP. When individuals are studied the value of hsCRP becomes less clear. The within-person daily variation of hsCRP is high and thus measuring hsCRP at any single time point can be misleading since the value can fluctuate significantly. Some have argued that measuring hsCRP does not give an accurate picture of risk but rather just gives a random snapshot in time that does not adequately represent the patient's real average inflammatory state. However, despite its shortcomings, hsCRP is used by many physicians. The value of this testing is touted as being useful in those patient in which high levels of hsCRP are found but who have no history of heart disease. In these cases it is thought that it can help unmask or uncover at-risk patients whose other vital signs and lipid values may be normal. The goal of testing is to use hsCRP as an additional risk marker in an effort to find patients who may be high risk for AMI, stroke, or peripheral vascular disease but whose conventional risk markers (age, blood pressure, lipids) are within normal limits.
Nephelometry and immunoturbidimetric measurement methods provide lower limits needed for hs-CRP assays. Some general guidelines for hs-CRP in prediction of risk for CVD are listed below:
  • <1.0 mg/L Low CVD risk
  • 1.0-3.0 mg/L Average risk for CVD
  • >3.0 mg/L High risk for future CVD
Perhaps a more established role for hsCRP is in patients with diagnosed ACS or stable coronary disease. In these patients hsCRP can be used to predict future coronary events.
It is important to note that the hsCRP and CRP assays are different and should not be used interchangeably. Clinicians often order the wrong test given that the two are similarly named. Many clinicians don't realize that although the CRP analyte is the same, the assays are very different. They may be trying to detect CVD using a CRP assay, which is not possible.
For hsCRP results that are very high (>10.0 mg/L) patients should be evaluated for an acute inflammatory condition (one unrelated to CVD).