Rose Bengal test is a rapid test that was originally designed to screen animal populations but is also used as an adjunctive test for rapid diagnosis of brucellosis in humans.
The Rose Bengal test (RBT) is a simple, rapid slide-type agglutination assay performed with a stained B. abortus suspension at pH 3.6–3.7 and plain serum. Positive results are generally confirmed by the standard agglutination test (SAT). Although the overall sensitivity reported for RBT varies widely, with the use of good quality antigens made by experienced or reference laboratories, the sensitivity of RBT can be increased.
Rose Bengal test is often used as a screening test in human brucellosis and would be optimal for small laboratories with limited means. False-negative reactions occur especially in the early stages of acute infection.
Procedure of Rose Bengal Plate Test:
- Test Serum (0.03 ml) is mixed with an equal volume of antigen on a white tile or enamel plate to produce a zone approximately 2 cm in diameter.
- The mixture is agitated gently for four minutes at ambient temperature, and then observed for agglutination.
- Any visible reaction is considered to be positive.
Limitation of Rose Bengal Test:
- Low sensitivity particularly in long evolution (chronic) cases
- Relatively low specificity in endemic areas. Because of this low specificity and the consequent large numbers of false positives, the use of the Rose Bengal test for screening in endemic areas is not recommended.
- Use of this test as the sole determinant of active infection would lead to unnecessary treatment with potentially toxic agents.
- Moreover, some authors consider that prozones make strongly positive sera appear as negative in RBT.
The test is very sensitive and positive samples should be checked by the complement fixation test (CFT) or by an IgG-specific procedure such as ELISA. The RBT can be used in all animal species but positive results should be confirmed by a quantitative test.