Utility Of Genexpert And Cytomorphology In The Diagnosis Of Extra Pulmonary Tuberculosis -At Kenyatta National Hospital

Abstract

BACKGROUND: Tuberculosis (TB) is one of the most common public health challenges in Kenya. Both pulmonary and extrapulmonary TB (EPTB) is an issue of concern. The advent of Human Immunodeficiency Virus (HIV) in Kenya has resulted into increased cases of extra pulmonary tuberculosis and it remains a diagnostic challenge. Cytology and conventional Ziehl Neelsen (ZN) smear have shown low specificity and sensitivity in diagnosis of EPTB respectively. Mycobacteriological culture and drug susceptibility testing are not always available in limited resource settings, hence the need for more rapid and reliable methods. Objective: In this study, we evaluated the performance of Cytomorphology, GeneXpert and ZN, for the diagnosis of cases suspected of EPTB refered to Fine Needle Aspirate Clinic (FNA) at Kenyatta National Hospital (KNH), Nairobi Kenya. Methods: FNA was collected from presumptive EPTB cases. Two smears were prepared from each aspirate and processed for cytology and conventional ZN microscopy smear. The remaining aspirate was treated with 2 mls of 20%NaOH and allowed to stand for a minimum of 30 minutes. The bacilli were then floated using 0.5mls of xylene and scooped, and transferred to 2mls of Normal saline for GeneXpert test. The Performance of the tests was calculated using R software version 3.2.2. (1) Bayesian method, the software is used in the absence of a gold standard or reference standard test Result: There were 50 TB suspected cases recruited in this study, but only 43 were analyzed. The mean age was 26.74 years (SD ± 14.146) with the range of 2 to 56 years. The majority of them (25.6%) were aged between 21 to 40 years and 55.8% were male. Out of the 43 TB suspected cases analyzed, 10(23.3%) were confirmed by GeneXpert, 25(58.1%) were suggestive for TB by cytomorphology and one, 1 (2.3%) was positive by ZN microscopy. Sensitivity and specificity of tests in this study sample size were: cytomorphology 25(56.9%) and 18(36.7%), ZN 1(4.9%) and 42(94.4%) and GeneXpert 10(25.6%) and 33(66.2%). Cytomorphology showed the lowest specificity (36.7%) while ZN microscopy smear showed the lowest sensitivity of 4.9%. Among the 10 positive by GeneXpert, 10 were also suggestive for TB by cytomorphology and one was positive by ZN microscopy. Conclusion: Our findings indicated that GeneXpert MTB/RIF test is a useful tool for the detection of MTB with reasonable sensitivity and specificity on EPTB fine needle aspirate with good performance as compared to cytomorphology and ZN smear microscopy