Dual testing for the serodiagnosis of syphilis; an abbreviated complement-fixation method.

Since the publication of the original complementfixation test for syphilis by Wassermann, Neisser, Bruck, and Schucht (1906) and the publication of the flocculation test of Porges and Meier (1908), innumerable modifications have been described for the improvement of both diagnostic methods. The technical complexity of the former furnished an incentive for the development of the latter. Yet, despite the daily titrations and adjustment of reagents, and despite the minute measurements required, the complement-fixation test was easy to read; whereas toe easily assembled flocculation tests were difficult to read and, often, more difficult to interpret. It is, however, probable that had a good flocculation test been first in the field, the complement-fixation test for syphilis would never have achieved more than academic recognition as an amazing reaction involving the tissues and bodyfluids of ox, sheep, rabbit, guinea-pig, and syphilitic man. From all the attempts that have been made to perfect the specificity and sensitivity of alternative tests to the Wassermann, there has emerged the conviction that, for the serodiagnosis of syphilis, no single test suffices, but that confidence is most wisely placed in an opinion based upon the results of both a flocculation and a complement-fixation test. The dual control is necessitated, primarily, by a phenomenon characteristic of all flocculation tests. Although generally admitted to be more sensitive than the complement-fixation test, they exhibit, on occasion, the so-called " prozone reaction ". This phenomenon occurs when the antibody present greatly exceeds in amount the antigen used. The antigen-antibody reaction is inhibited or obscured and the test fails. The prozone reaction is never encountered in the complement-fixation test, provided the serum volume is small (0-05 ml. to 0 1 ml.), but can be demonstrated by increasing the serum volume to 0 5 ml. The proportion of sera exhibiting a prozone reaction in the standard flocculation test used in this laboratory (Ford Robertson and Colquhoun, 1939) is extremely small. In a survey by Colquhoun, Kyles, and Rannie (1945) extending over a period of 16 months, using in full both the standard flocculation and Wassermann tests, 8,342 sera were investigated. Of this number, 26 yielded a negative result in the flocculation test and a positive result in the complement-fixation test. Both tests showed agreement in 6,853 cases. The fact that such discrepancies can occur is the most cogent argument in favour of including a complement-fixation test as one of those employed in the serodiagnosis of syphilis. The present-day use of extremely sensitive flocculation tests as " screen" tests can only result in repeated failures to detect prozone cases and is, therefore, indefensible. Notice must also be taken of those cases in which the flocculation test yields a positive and the complement-fixation test a completely negative result. In the survey referred to this occurred in 51 cases. When, for these reasons, it is thought desirable to submit large numbers of sera to both flocculation and complement-fixation tests, it becomes a matter of urgency to study ways and means of eliminating unnecessary work and of expediting essential procedures. Further, although, in serological work great speed is not conducive to accuracy, fatigue and tedium are even more inimical to precision. The following outline of a system of performing both flocculation and complement-fixation tests on the same sera is not complete: its purpose is to describe timeand fatigue-saving procedures that have yielded excellent results over a long period.