THE ANTISTREPTOLYSIN TITER

The antistreptolysin O titer is used to provide evidence of the recent occurrence of a streptococcic infection. A rise in titer of this antibody is first detectable one to two weeks after onset of the infection, and the maximum titer is attained at about four weeks. Thereafter, the titer declines gradually at a rate that is variable but much slower than the rate of the initial increase. Because of the almost universal exposure to streptococcic infections, measurable quantities of antistreptolysin are found in a high proportion of older children and adults. Consequently, in using the test for diagnostic purposes, the demonstration of an increase in titer in successive serum samples or the occurrence of a very high titer is of more significance than a slightly elevated titer (100-200 units) in a single serum specimen. The test has its most important application in the differential diagnosis of rheumatic fever. When the