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Polymerase chain reaction for Mycobacterium tuberculosis complex DNA. Use on negative archival Ziehl-Neelsen
L Vago1, P Zerbi, R Caldarelli-Stefano
1Pathology Unit, L. Sacco Institute of Biomedical Sciences, University of Milan, Italy. gianluca.vago@unimi.it
Objective:
To evaluate the usefulness of a nested polymerase chain reaction (PCR) for Mycobacterium tuberculosis complex on routinely stained cytologic samples from patients with extrapulmonary tuberculosis.
Study Design:
Nested PCR for the detection of a fragment of the IS6110 insertion sequence of M tuberculosis complex was applied to Ziehl-Neelsen-negative archival cytologic slides of serous effusions (pleural [n = 7], peritoneal [n = 1] and pericardial [n = 1]) and a lymph node fine needle aspirate (n = 1) from nine human immunodeficiency virus (HIV)-positive patients with autopsy-proven active extrapulmonary tuberculosis. Malignant effusions and aspirates from nine HIV-positive patients with non-Hodgkin's lymphoma and pleural effusions from seven HIV-negative patients with heart failure were used as controls. DNA was extracted after removing the coverslip and gently scraping the cytologic sample from the slides.
Results:
In all cases, enough DNA was obtained for PCR without any significant loss of integrity, as demonstrated by PCR positive for HLA-Dq. PCR for M tuberculosis was positive in 8 of the 10 samples (80%) from patients with tuberculosis but also in three samples (30%) from HIV-positive patients in the control group. None of the samples from the HIV-negative patients was positive.
Conclusion:
PCR for M tuberculosis can be reliably performed on archival cytologic slides from extrapulmonary samples, but although it is highly sensitive, it may lead to positive results in immunocompromised patients without any sign of active tubercular disease.