THE LUPUS DIAGNOSTIC TESTS: ANA: Antinuclear antibodies and other "Anti-"

The patient with SLE, or lupus is often first referred to a rheumatologist for diagnosis based on the result of a positive blood test for antinuclear antibodies (ANA). The ANA is the "sine qua non" of lupus, meaning that virtually every patient with SLE will have a positive ANA, yet the blood test is by no means "specific". This means that some 5% of the population may have a positive ANA but never develop lupus. In general, the higher the antibody titer value, the high the probability of SLE. A more specific blood test is the "anti-double stranded, or native, DNA". Finding this antibody in the patient's very genetic material makes the diagnoses of SLE more probable, and its presence may predict current or future involvement of the kidney. Perhaps the most specific antibody is "anti-Smith", names after the patient in whom it was originally found. This test is nearly 100% predictive of SLE if it is present, but it is only found in less than 20% of patients.


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