Over 15 years ago, the AHA and CDC recommended the measurement of hs-CRP as an aid in the diagnosis and treatment of CVD. Physicians and providers sometimes use hs-CRP to help uncover primary or secondary cardiovascular disease. The marker is also used to counsel patients on their risk and some use the marker to monitor cardiovascular health over time. hs-CRP can be elevated in heart failure, atrial fibrillation, arterial hypertension, and heart valve pathology in addition to coronary artery disease. It may have a role in the prognosis of coronary stent thrombosis or restenosis as well.
However, there is debate surrounding the use of hs-CRP. While most large laboratories offer assays for CRP, hs-CRP now has less demand. Large studies are showing that hs-CRP is, in fact, elevated in patients who have real cardiovascular risk. However, these studies are population studies comparing large groups with high hs-CRP to large groups of people with low hs-CRP. When individuals are studied, the value of hs-CRP becomes less clear. The within-person daily variation of hs-CRP is high and thus, measuring hs-CRP at any single time point can be misleading since the value will fluctuate significantly. Some have argued that measuring hs-CRP 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, hs-CRP is still used by some physicians. The value of this testing is touted as being useful in those patients in which high levels of hs-CRP are found but who have no history of heart disease. In these cases, it is thought that hs-CRP testing 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 hs-CRP as an additional risk marker in an effort to find patients who may be at 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 the 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 hs-CRP is in patients with diagnosed ACS or stable coronary disease. A hs-CRP test may help gauge risk for people who have a 10% to 20% chance of having a heart attack within the next 10 years.
It is important to note that the hs-CRP 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 protein is the same, the assays are very different. They may be trying to detect CVD using a CRP assay, which is not possible.
Note for hs-CRP results that are very high (>10.0 mg/L), patients should be evaluated for an acute inflammatory condition (one unrelated to CVD).
