Background - Smear-negative TB (SNTB) may remain undetected for a long duration and new bio-markers are needed for diagnosis. Our study investigated monocyte parameters in this regard.Thirty cases each of SNTB, sputum positive cases and healthy controls were included. Full blood count and immune-phenotyping for 'monocyte parameters' by flow cytometry were performed using CD45, CD16, CD14, CD64 and HLA-DR The percentage of monocyte subsets and MFI of CD64 and HLA- DR noted and data statistically compared.The monocyte to lymphocyte ratio, percentage of intermediate monocytes, expression of CD64 on total as well as intermediate monocytes were significantly elevated in cases with SNTB as compared to healthy controls (p value, 0.07, 0.07, 0.001, 0.001 respectively). The cut off value for MFI CD64 on total and intermediate monocyte was >18 and >19.6 respectively.Thus monocyte parameters can serve as useful biomarkers for diagnosing tuberculosis in the sputum negative group.
Keywords: Diagnosis; Flow cytometry; Intermediate monocytes; MFI CD64; Monocyte lymphocyte ratio; Pulmonary TB; Smear negative.