Testing–testing: CRP–hs or unleaded?
C-Reactive Protein
CRP is a lab test which can used to monitor inflammation. It is a non-organ specific acute phase response protein (acute phase response = pathophysiologic changes which accompany inflammation). It can be used in a variety of clinical settings when an inflammatory process is a concern. CRP levels can rise in acute infection, but the test is also ordered in chronic inflammatory diseases (inflammatory bowel disease, rheumatoid arthritis, lupus to name a few) as a measure of degree of inflammation or as a way to measure treatment effectiveness. CRP can be ordered as a measure of prognosis in certain malignancies.
CAD Risk Assessment
Since the early nineties, CRP has been studied as a serum marker for cardiovascular risk assessment. In the Physicians Health Study in 1997, baseline CRP concentrations were higher in men who went on to develop myocardial infarction (1.51 mg/L vs. 1.13 mg/L, RR = 2.9).1 Similar findings have been subsequently reported in other studies although the risk and CRP value differed. CRP is a similar (some would argue slightly less impressive) predictor of risk for coronary heart disease as blood pressure and serum cholesterol. (2) The elevation in CRP used for risk assessment is slight compared to the orders of magnitude increase above base line values seen in acute/chronic inflammation. Therefore, a separate standard curve/calibration is typically used- “hsCRP”. However, the specimen collection requirements are the same. (Depending on lab (1 mL serum)- Red Top tube. Gel-barrier tube, Green top (Na/Li), Lavender Top, Pink Top). This is called the hsCRP or high-sensitivity CRP. Therefore, the hsCRP should be ordered when assessing cardiovascular risk. “Classically” two samples are drawn two weeks apart.
Test Risk Intervals
<1 mg/L = LOW RISK
1-3 mg/L = intermediate
>3 mh/L = high risk ( but …check your local lab reference values!!!!!!!!)
Subsequently, investigations into the molecular pathophysiology of variance in CRP expression has shown a possible link between genetic polymorphisms in CRP (or proteins influenced/related to CRP) and cardiovascular risk as summarized below.(3-5)
“Healthy subjects tend to have rather stable, individual,
baseline CRP concentrations, that are significantly (35–40%)
heritable. Although no deficiency or protein polymorphisms of CRP have
yet been identified, associations between CRP production and genetic
polymorphisms in IL-1 and IL-6 have been suggested.”(5)
Therefore, there may be a point in the not too distant future when we
are studying a specific group of polymorphisms in the molecular lab on
a routine basis to assess cardiac risk.
References
1. N Engl J Med. 1997 Apr 3;336(14):973-9
2. N Engl J Med. 2004 Apr 1;350(14):1387-97
3. Atherosclerosis. 2005 Jan;178(1):139-45
4. J Am Coll Cardiol. 2007 Sep 18;50(12):1115-22. Epub 2007 Sep 4
5. QJM. 2003 Nov;96(11):793-807
No Comments Yet