A test that measures the levels of a pair of proteins on the surface of red blood cells may help doctors diagnose systemic lupus erythematosus (SLE, or lupus) earlier and more accurately, according to a study supported in part by a grant from the Alliance for Lupus Research (ALR). Diagnosing lupus is often difficult because there is no definitive test for the disease and its manifestations often mimic those of other illnesses. Findings from the study of a promising new diagnostic test developed by ALR-funded investigator Joseph M. Ahearn, MD, Suzan Manzi, MD, MPH, and their colleagues at the University of Pittsburgh were published in the November 2004 issue of Arthritis & Rheumatism.
In this study, the researchers measured the levels of two proteins, C4d and CR1, on samples of red blood cells from 100 people with lupus, 133 people with other diseases, and 84 healthy individuals. C4d and CR1 are part of the complement system—a group of blood proteins known to play a role in lupus. Drs. Ahearn, Manzi, and colleagues found that lupus patients have abnormally high levels of C4d and abnormally low levels of CR1 on the surface of their red blood cells compared to healthy people and people with various other diseases, including several other autoimmune and rheumatic diseases.
Unlike the most widely used laboratory tests for SLE, the test for C4d and CR1 levels is both sensitive and specific, meaning that it detects the majority of patients who have lupus and that most people with a positive test result actually have the disease. “We compared our test to traditional ‘gold standard’ blood tests for lupus, like ANA [antinuclear antibodies] and anti-double-stranded DNA antibodiesÉand it performed better on a single clinic visit in diagnosing lupus compared to these other tests,” says Dr. Ahearn. The researchers’ next step is to examine whether the test can accurately identify patients whom lupus experts believe have the disease but who don’t meet the official diagnostic criteria for lupus, which many experts believe are outdated, Dr. Manzi says.
What it means for people with lupus: “This test may be a useful addition to the current armamentarium of blood tests that are now used to try to diagnose lupus,” says Dr. Ahearn. “Our ability to diagnose lupus is very imperfect,” adds Dr. Manzi. “We’re missing people who have the disease and we’re probably diagnosing [some] people that don’t have the disease. Anything that will increase the accuracy of diagnosis is going to be beneficial for patients.” With support from the ALR, Drs. Ahearn, Manzi, and colleagues are pursuing additional studies aimed at using this test to monitor disease activity and predict flares, which could help doctors make decisions about treatment. “Our ultimate goal is to translate this test into kit form,” says Dr. Ahearn, making it practical and affordable for use in settings such as a doctor’s office or medical laboratory, both for diagnosing lupus and monitoring disease activity.
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