Use of glycerol as an alternative to freeze-drying for long-term preservation of antigen for the direct agglutination test.

The potential of glycerol for long-term preservation of the direct agglutination test (DAT) antigen was evaluated at a fluctuating laboratory temperature of 25-37 degrees C and at constant temperatures of 37 and 45 degrees C for a period of 222 days. DAT titres recorded for the three antigen aliquots preserved in 50% (v/v) glycerol and stored at 25-37, 37 or 45 degrees C at 11 time intervals were within the same range of the control antigen kept at 4 degrees C. Performance of the glycerol-preserved antigen stored at 45 degrees C was compared with that of a freeze-dried version on 24 visceral leishmaniasis (VL) and 54 non-VL patients.