Modified Widal test using 2-mercaptoethanol for detecting anti-salmonella IgM in febrile patients

Abstract

Introduction: Despite limitations, the Widal test is widely used in resource-constrained settings because it is fast, inexpensive and user-friendly. Therefore, efforts continue to improve its diagnostic utility. Aims: Using 2-mercaptoethanol (2-ME) to detect the IgM fraction of total agglutinins detected by the Widal test in the serum of febrile patients. Materials and Methods: Single serum specimens were collected from 333 patients presenting to our hospital with fever. One aliquot of serum was tested by standard Widal test; a positive result was defined as simultaneous elevation of ‘O’ and 'H' titres to 1:80 or above. A second aliquot was simultaneously tested by a modified Widal test in which serum was diluted in isotonic saline with added 2-ME (0.12M) instead of in plain isotonic saline. Differences in titre between the two versions of Widal test were noted. A four-fold or greater reduction in titre upon testing with 2-ME, was considered evidence of specific IgM. Results: Standard Widal test was positive in 55 (16.5%) out of 333 patients. A ?4-fold reduction of ‘O’ titre in modified Widal test was found in 38 (69.1%) out of 55 cases, indicating the presence of specific IgM. A similar reduction of 'H' titre was seen in only 6 (11%) out of 55 cases. Conclusion: Simultaneous use of standard Widal test and modified Widal test with 2-ME allows the detection of specific IgM at a low cost. This can increase the diagnostic utility of the Widal test. Keywords: Acute febrile illness, Typhoid fever, Serology, IgM, Laboratory diagnosis.