Sometimes blood clots form where they’re not supposed to, such as in a vein or artery. When that happens, it can cause serious problems by interfering with proper blood flow. These type of inappropriate clots, called thromboses, have the potential to cause strokes, pulmonary embolisms (when a blood clot breaks off and travels to the lungs), and miscarriages (which can happen if a clot blocks blood flow in the placenta).

People with lupus, a chronic autoimmune disorder, face a higher than average risk of thromboses, often because they have abnormal antibodies such as lupus anticoagulant (LAC) that make blood more likely to clot. Low levels of C3 (a blood protein) has also been associated with clotting risk in lupus.

Scientists at Johns Hopkins (working with Exagen) have identified a new biomarker, called PC4d, that aims to identify which lupus patients have an especially high risk of blood clots. According to their research, a composite risk score that considers levels of PC4d — as well as low C3 and LAC — can be used to predict which lupus patients will develop a thrombosis. However, using the other biomarkers (low C3 or LAC) alone may also be useful.

A new study, led by Michelle Petri, MD, professor of medicine at the Johns Hopkins University School of Medicine and director of the Hopkins Lupus Cohort, looked at data on more than 140 lupus patients and found that 16 of them had had a thrombosis within the prior five years. They then took blood and serum samples from all the participants to evaluate how individual biomarkers and/or a composite biomarker score aligned with clot risk.

Their study, published in in the journal Lupus Science & Medicine, concluded that “a composite thrombosis risk equation including PC4d, low C3 and LAC strongly associates with thrombosis in [lupus].” Although viewing all these biomarkers together provided some additive value, they also found that each of them “were all significantly and independently associated with any thrombosis.” This means that any one of these biomarkers might be useful on its own. In particular, “low C3 was the strongest risk factor for any thrombosis,” they reported.

The authors noted that their study has several limitations, including the design (they did not continue to follow patients after the biomarkers were measured) and the small number of thromboses that occurred, so more research is needed.

If you have lupus and are concerned about your risk of blood clots, talk to your doctor. Ask about which tests you should consider and whether you ought to be taking a blood-thinning medication to reduce your risk of blood clots.

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