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We were interested in the study by Berthelot and colleagues, in which they studied the predictive value of the antiperinuclear factor (APF) for rheumatoid arthritis.1
The authors concluded that APFs are useful in the diagnosis of early rheumatoid arthritis. They mentioned that recognition of the true value of APF has long been hindered by methodical errors. Serum samples were only diluted 1:5 or 1:10, even though the APF titre can reach 1:20 000 in rheumatoid artritis serum samples and is usually above 1:200.
We would like to make some comments especially concerning the method they used. The method used differs not only in the dilution of the serum samples, for screening 1:100 and if positive they were further diluted 1:200, 1:500, 1:1000 to determine the end point titre, but it differs also in the way of regarding the positivity of the tests. They refer to their study published in 1990, in which a …