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Updated: Aug 19, 2026
Immuno-fluorescence Assay of Leptospiral Surface-exposed Proteins
Published on: July 1, 2011
Use of formaldehyde-PBS for serum dilution in the microscopic agglutination test (MAT) for leptospirosis
Abstract:
Altogether, 431 sera (381 positive and 50 negative sera) were tested against different Leptospira serovars in the microscopic agglutination test (CMAT) using PBS with and without formaldehyde for comparative purposes. For the preparation of serum dilutions with formaldehyde-PBS, formaldehyde was added to PBS at a final concentration of 0.4%. When retested after storage, 234 from the 381 formerly positive sera gave positive, 68 doubtful and 79 negative results in the MAT. Out of the 234 sera with positive reaction in MAT, 212 (90.6%) showed positive reactions in the MAT with formaldehyde as well, 19 (8.1%) doubtful reactions and 3 (1.3%) became negative. All sera with negative reaction in the routine MAT were found to be negative in the MAT with formaldehyde as well.
Insights
Formaldehyde in phosphate-buffered saline (PBS) can preserve the reactivity of Leptospira microscopic agglutination test (MAT) sera. This method shows promise for maintaining diagnostic accuracy of Leptospira serovars in stored samples.
Area of Science:
- Veterinary Microbiology
- Immunoserology
- Bacteriology
Background:
- The microscopic agglutination test (MAT) is a standard method for diagnosing leptospirosis.
- Preservation of serum samples is crucial for maintaining the stability of antibodies against Leptospira serovars.
- Formaldehyde is a potential preservative agent that may impact serological test results.
Purpose of the Study:
- To evaluate the effect of formaldehyde on the stability and reactivity of sera in the microscopic agglutination test (MAT).
- To compare the diagnostic performance of MAT using phosphate-buffered saline (PBS) with and without formaldehyde.
- To assess the utility of formaldehyde as a preservative for Leptospira MAT.
Main Methods:
- A total of 431 sera (381 positive, 50 negative) were tested against various Leptospira serovars using MAT.
- Serum dilutions were prepared in PBS containing 0.4% formaldehyde and compared with PBS alone.
- Sera were retested after storage to evaluate the preservative effect of formaldehyde.
Main Results:
- Of 381 initially positive sera, 234 remained positive upon retesting.
- When tested with formaldehyde, 212 (90.6%) of the 234 positive sera maintained positive reactions.
- All initially negative sera remained negative when tested with formaldehyde.
Conclusions:
- Incorporating formaldehyde (0.4%) into PBS for serum dilutions appears to preserve the reactivity of positive sera in the MAT.
- Formaldehyde-treated PBS shows potential as a stabilizing agent for Leptospira MAT, with minimal impact on positive and negative results.
- This approach could enhance the reliability of MAT for diagnosing leptospirosis, especially with stored serum samples.
