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Abstract - The false sero-negativity of brucella standard agglutination test: Prozone phenomenon
Hasan Karsen, Nebi Sökmen, Fazilet Duygu, İrfan Binici, Hüseyin Taşkıran


The false sero-negativity of brucella standard agglutination test: Prozone phenomenon

Hasan Karsen1, Nebi Sökmen2, Fazilet Duygu3, İrfan Binici4, Hüseyin Taşkıran5

1Harran University School of Medicine, Department of Infectious Diseases and Clinical Microbiology, Şanlıurfa, Turkey

2Aydın Family Health Center, Aydın, Turkey

3Tokat State Hospital, Clinical Infectious Diseases, Tokat, Turkey

4Yuzuncu Yil University School of Medicine, Dept. Infectious Diseases and Clinical Microbiology, Van, Turkey

5Nizip Private Zirve Medical Center, Nizip, Turkey


Objectives: We aimed to assess prozone phenomenon that is quite rare and causes false negativity in serological diagnosis of brucellosis with standard dilution titers.

Materials and methods: In this study the tests of four cases that have false negative serological results were evaluated. Blood cultures were obtained from all cases while cerebrospinal fluid cultures were studied in the two cases. Standard agglutination test (SAT) and Coombs test were performed to all patients.

Results: SAT and Coombs test was negative in titers up to 1/640 in all cases. The SAT and Coombs tests in cerebrospinal fluid (CSF) of the two cases with neurobrucellosis diagnosis were negative, as well. Since the clinical and laboratory findings suggested the brucellosis, the serums were restudied by diluting up to 1/10240 titer and we saw that the first 3 cases became positive at a titer of 1/1280. The fourth case remained negative and therefore, we applied high dilution Coombs test. This time the test gave a positive result at 1/10240 titer beginning from 1/2560 titer. B.melitensis was isolated from two cases.

Conclusion: SAT and Coombs’ test must be diluted to titers 1/2560 or more in order to exclude false sero-negativity in cases with clinical and laboratory findings suggesting brucellosis. J Microbiol Infect Dis 2011;1 (3):110-113

Key words: Brucellosis; prozone phenomenon; standard agglutination test; Coombs test

Volume 01, Number 03 (2011)