Interlaboratory variability of the antiperinuclear factor (APF) test for rheumatoid arthritis

The antiperinuclear factor (APF) test is as sensitive and specific for rheumatoid arthritis as the classical rheumatoid factor tests. Five European laboratories decided to perform a consensus study on the interlaboratory variability of the APF test. They used different donor cells, different conjugates and different criteria for positivity. However, the results differed by not more than one two-fold dilution step, when expressed in international units using WHO reference rheumatoid arthritis serum as the standard.