Comparative evaluation of freeze-dried and liquid antigens in the direct agglutination test for serodiagnosis of visceral leishmaniasis (ITMA-DAT/VL).
OBJECTIVE
The direct agglutination test (DAT) for visceral leishmaniasis (VL) with liquid (LQ) antigen is known to be only moderately reproducible because of inter-observer and batch-to-batch variability as well as its sensitivity to temperature and shaking during transport. We evaluated a DAT with freeze-dried (FD) antigen and compared it with the LQ antigen version.


METHODS
Blood samples of clinical VL suspects and healthy endemic controls were collected in Sudan, Nepal and India. Both test versions were performed in duplicate in the respective countries and in the reference laboratory. Interbatch variability and stability tests were conducted and agreement was examined within and between centres on a dichotomic scale by Cohen's kappa as well as on a continuous scale through Bland-Altman plots.


RESULTS
The FD antigen remains fully active even after storage at 45 degrees C for 24 months. Using a cut-off titre of 1:6400, the agreement between the FD and the LQ formats was excellent.


CONCLUSIONS
The major advantages of FD antigen are its better stability at higher temperatures and its longer shelf life, which make it much more suitable than the LQ version for use in the field.
Jacquet
Diane
D
Applied Technology and Production Unit, Institute of Tropical Medicine, Antwerp, Belgium. djacquet@itg.be
Boelaert
Marleen
M
Seaman
Jill
J
Rijal
Suman
S
Sundar
Shyam
S
Menten
Joris
J
Magnus
Eddy
E
D000372:Agglutination Tests / Q000379:methods; D000818:Animals; D000953:Antigens, Protozoan / Q000276:immunology*; D004355:Drug Stability; D005612:Freeze Drying; D006801:Humans; D007893:Leishmania donovani / Q000276:immunology*; D007898:Leishmaniasis, Visceral / Q000175:diagnosis*; D015203:Reproducibility of Results
D000953:Antigens, Protozoan