Effect of rust on haemagglutination test.

Microtechniques are now used extensively in diagnostic as well as immunological studies for viruses, protozoa, and bacteria (Sever, 1962; Edwards, 1964; Kessel, Lewis, Pasquel, and Turner, 1965). In microtitrations constant volumes of fluids are picked up and delivered by specially constructed and calibrated metallic microdiluters. According to the Microtiter Instruction Manual of the Cooke Engineering Company (1965), their high titanium, stainless steel, new-pattern microdiluters with a precisely slotted tip are not supposed to rust, but in the hot and humid climate of Calcutta they do rust, though they continue to deliver fluids properly when tested on the special 'go-no-go' delivery tester supplied by the manufacturer. Many of the rust particles become detached from the microdiluters during their agitation in the wells of the dilution plates and produce, both with human group 0 and goose erythrocytes, an atypical settling pattern at the bottom of disposable plastic V plates. There is a small central button of erythrocytes, showing as well as the peripheral deposit, small black particles rimmed by a clear space. The peripheral concentric erythrocyte deposit closely simulated the typical haemagglutination pattern. Microscopically many black rust particles of various sizes and shapes were observed among discrete erythrocytes, and we have called this atypical pattern pseudohaemagglutination. The rusted particles did not alter the typical agglutination pattern or the titre of some of the haemagglutininpositive enteroviruses and arboviruses. They, however, produced pseudo-haemagglutination with the haemagglutinin-negative enteroviruses as well as the uninoculated tissue culture maintenance medium. It appears that the rusted microdiluters, if used for diluting the antisera or the haemagglutinin-positive antigens, are not likely to modify the positive haemagglutination patterns. But one has to be cautious in using the rusted microdiluters for screening antigens as the detached rust may of itself produce a false-positive haemagglutination pattern.