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What are the causes for a positive ANA test during pregnancy?

Q: I am 28 weeks pregnant with my second child. My blood type is B negative. I have received Rhogam 4 times in my lifetime, once after a miscarriage (at 6 weeks), once during my first pregnancy, after the birth of my first child and about 1 and a 1/2 weeks ago for this pregnancy. At my last check up, the doctor performed the usual dipstick test and found protein in my urine. She asked me to do a 24 hour urine test, which came back with a level of 455. I don't have high blood pressure, my creatine levels are normal and my CBC was normal. My obstetrician then referred me to a nephrologist. The nephrologist told me to undergo an ANA test, which came positive. All the other blood work done for the kidney function panel were normal. The nephrologist told me to go for lupus test, even though the only symptom of lupus that I have is protein in my urine. Is Anti D, the substance in Rhogam shots, considered an anti nuclear antibody? If so, would it cause my ANA test to be falsely positive?

A:Anti-nuclear antibodies (ANA) are an unusual type of gamma-globulins found in patients with certain autoimmune diseases. ANAs are directed against certain components found in the nucleus of a cell in the body. They are found in patients whose immune system is predisposed to cause inflammation against their own body tissues (autoimmune diseases). An ANA test is needed if there is a reasonable suspicion of SLE from history, physical findings or the results of routine tests such as the CBC (leukopaenia, thrombocytopaenia) as ANA may be found in a variety of conditions and in normal individuals. The random chance of a false positive in normal individuals is considerably greater than a true positive, unless the clinician selects only individuals with a reasonably high possibility of having the disease before testing. Therefore, careful selection of patients to be tested is of great importance as improper use of ANA testing can lead to misinformation, incorrect diagnoses and a waste of money. This is because, even with the newest tests, about 5% (1 out of 20) of normal individuals will give a weakly positive result and ANA should never be ordered as a routine screening test. A positive ANA result in a patient with no or minimal features of SLE can be misleading or worse because it may cause the clinician to order unnecessary tests. It is possible that anti-D is non-specifically binding and giving a false positive test result. One can go for immunofluorescence based tests in case ANA is coming positive with ELISA.

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