A primer on testing for c-reactive protein

Doctors are now using a high sensitivity blood test for the inflammatory marker C-reactive protein (CRP). C-reactive protein (CRP) is an immune system chemical that the liver manufactures in response to inflammation in the body. Testing for CRP may help predict your risk of heart attack or other heart conditions.

As yet, there is no agreement about exactly when the test should be used, or who should have it. Plus, the presence of other inflammatory conditions will often raise CRP levels.

Nonetheless, CRP may be requested as one of several tests for a cardiovascular (heart and blood vessel) risk profile, often along with lipid (fat) tests, such as those for cholesterol and triglycerides.

Some experts say that the best way to predict risk is to combine a good marker for inflammation, such as CRP, along with a person's low-density lipoprotein (LDL) cholesterol levels. The theory is that, while LDLs say how much plaque is clogging your arteries, your CRP may tell you how likely that plaque is to burst, causing a dangerous blood clot.

If you get tested for CRP here's a quick breakdown of what your results mean:

• Under 1mg/l is a low reading.
• 1–3mg/l is an average reading.
• Above 3mg/l is considered a high reading.

Chronic inflammation occurs when the immune system's powerful defences are switched on — and stay on.

Doctors have discovered many things that can cause chronic inflammation in the arteries: everyday infections, such as gum disease or the stomach ulcer bacterium H. pylori; substances released by excess stomach fat; and simple aging.

Chronic inflammation is bad for the heart because it contributes to plaque buildup in the arteries. This is how it happens. When inflammatory chemicals discover LDL particles in artery walls, they send macrophages to eradicate the unwelcome cholesterol. The by-products of this attack are foam cells (oxidized LDL particles) that form the basis of plaque. As plaque grows, it develops a hard, fibrous cap, but inflammatory compounds can weaken this protective lid, making it susceptible to rupturing and releasing plaque into the bloodstream.

Other inflammatory compounds encourage blood to clot and, if constant, low-grade inflammation results in a steady supply of these compounds into your bloodstream, which can also lead to a heart attack.

The link between internal inflammation and heart disease has emerged only recently. Now we know that chronic inflammation may help doctors to predict which patients with near-normal cholesterol levels could go on to have heart attacks.

So far, there are no drugs for chronic inflammation, although statins, beta-blockers and low-dose ASA may act as anti-inflammatories. Doctors are also exploring whether long-term, low-dose antibiotics are appropriate for people with low-grade, persistent infections.

Keep this primer on testing for c-reactive protein in mind when visiting your doctor to help you discuss whether testing is right for you.