Anticitrullinated protein antibodies: taking into account antibody levels improves interpretation

Hensvold et al1 reported on the discriminatory capacity of anticitrullinated protein antibodies (ACPA) for diagnosing rheumatoid arthritis (RA).1 A major strength of the study is that it was performed in a population setting and that a large number of controls (n=12 434) were included, thereby allowing a reliable estimate of the specificity of ACPA. The authors give detailed information on the diagnostic performance of anti-CCP2 antibodies (Euro-Diagnostica) for two cut-off points, namely the cut-off point recommended by the manufacturer and a cut-off point that is three times higher than the manufacturer's cut-off point. The latter high cut-off was defined in accordance to the European League against Rheumatism/American College of Rheumatology 2010 RA classification criteria.2 The authors show that the positive likelihood ratio (LR) was higher for the high cut-off (LR=74) than for the cut-off point recommended by the company (LR=33).

It is increasingly recognised...