Differential Agglutination Titre (D.A.T.) in Juvenile Rheumatoid Arthritis.

The technique employed from 1949-1956, which has been described by one of us (Scott, 1952), was a slight modification of the method originally proposed by Rose, Ragan, Pearce, and Lipman (1948). Since 1956, a further modification has been employed, as suggested by Greenbury (1957), using Perspex trays (M.R.C. pattern) in place of tubes and racks. This method will be described in detail elsewhere (Bywaters and Scott, unpublished). The results by the two methods are closely comparable, the newer method giving more consistent results. The results are expressed as a differential titre (ratio) in both methods, and the lowest ratio accepted as positive in a series of doubling dilutions is 1: 16. Slight changes in the sensitivity of the method have been found to occur because of variations in agglutinability of red cell suspensions from different sheep, amounting usually to not more than a one-tube difference. A single positive result occurring in the midst of a series of negative tests in one individual is therefore suspect and may well be due to technical factors, although in an attempt to control this, sera of known titre were included as a safeguard in each series of titrations.