Measuring the level of C-reactive protein monomer (mCRP) — a protein that increases in response to tissue damage and inflammation — may help identify those ANCA-associated vasculitis (AAV) patients who have cardiovascular disease, a recent study found.
People with AAV have an unwanted immune response that causes inflammation and damage to blood vessels. The C-reactive protein or CRP is often used to measure that inflammation, but this protein exists in two forms, and only one seems to relate to inflammation.
This CRP form, called CRP monomer or mCRP, also appears to be associated with the formation of blood clots, rupture of atherosclerotic plaques, and severe cardiovascular disease such as heart attacks. Together, that evidence supports the association of mCRP with cardiovascular disease in AAV patients.
To clarify this association, researchers at the Affiliated Hospital of Inner Mongolia Medical University measured the plasma levels of mCRP in 37 AAV patients, diagnosed between October 2018 to November 2019, and 20 healthy volunteers.
In both groups, there was an equal mix of males and females; the average ages were 58.5 years for the AAV group and 55.3 years for the healthy controls. In addition to mCRP levels and demographic information, the researchers also collected data regarding disease activity, the presence of additional conditions, and cardiovascular risk factors.
The results showed that mCRP levels were significantly higher in people with AAV (244 micrograms per milliliter, or mcg/ml) than in healthy individuals (170 mcg/ml).
But notably, these levels were particularly more elevated in the four AAV patients who also had a form of cardiovascular disease called acute ST-segment elevation myocardial infarction (STEMI) than in the AAV patients without STEMI (581 vs. 241 mcg/ml).
Of note, STEMI occurs when blood clots completely block a major coronary vessel — the vessels feeding oxygen to the heart muscle — and is usually associated with heart attack and death.
The researchers then showed a positive correlation between plasma mCRP levels and disease activity, as assessed with the Birmingham Vasculitis Activity Score (BVAS). In contrast, these plasma protein levels negatively correlated with the estimated glomerular filtration rate (eGFR), indicating that AAV patients with high mCRP had reduced kidney function.
The results also found a correlation between mCRP and brain natriuretic peptide (BNP) — a protein made by the heart and blood vessels that is typically high in heart failure patients — and other measures of heart function. That correlation suggests that AAV patients with cardiovascular illnesses have higher mCRP levels.
Importantly, CRP did not show any association with measures of heart function, highlighting that while both this protein and CRP are related to AAV disease, only mCRP might be a useful indicator of cardiovascular disease in patients.
“The level of mCRP is related not only to AAV disease but also to the occurrence of cardiovascular disease in patients with AAV,” the researchers wrote. “Therefore, mCRP can be used as a plasma biomarker of cardiovascular diseases in AAV.”
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