Can augmentin (amoxicillin and clavulanate) or predinsone create a slight false positive lab result for an autoimmune test?

Autoimmune test?: What test are you referring to? It is possible that an antibiotic like Augmentin (amoxicillin and clavulanate) may produce false positive results on some tests, and more likely that prednisone would produce false negative results, but this should be discussed with the doctor who ordered the tests.

No: No but Prednisone can suppress true positive results if given for long enough or at very high doses.

I would say no: Autoimmune studies typically are difficult to interpret. It's not that the laboratory is "wrong"; often the assay is detecting something that is truly there. What's harder to know is whether a positive test actually reflects the presence of real disease: referred to as positive predictive value(PPV). Drugs can interfere, but prob not false +'s. (False negatives, very well possible!).

No: If anything, very high-dose prednisone for a long duration may actually cause false negative test at times.