Objectives: The objective of this investigation was to find out if sputum-positive (AFB test) test, which is performed to assess mycobacterial infection status, is anyway correlated with any of the LDH isoforms. And if so, can it be used, either alone or together with sputum test, as a rapid on-the-spot marker for field diagnosis of tuberculosis. Design and methods: To analyze the relationship between sputum test results and the level of LDH isozyme (isoforms), 157 individuals were randomly selected from a Sahariya tribal population, with a known history of tuberculosis, for sputum and blood collection. The Ziehl–Neelsen’s staining of sputum smear was done as per RNTCP (Revised National Tuberculosis Control Programme) protocol. In all the samples, serum LDH level was estimated spectrophotometrically while the levels of individual isoforms were assessed on native PAGE. Results: The LDH content was significantly higher in blood sera of sputum-positive (three positive) individuals (444 ± 270 IU) as compared to sputum-negative samples (242 ± 125 IU). Analysis on the association of different LDH isoforms (LDH1, 2, 3, 4 and 5) with sputum test revealed significantly higher frequency of LDH2 and LDH3 in sputum-positive samples as compared to sputum-negative samples. In sputum three positive cases, however, the frequency of LDH3 appeared much higher (in 60% cases) than LDH2 (in 33% cases), which was found to be almost same in sputum negative but higher in two positive samples (44.4%). Conclusions: The present data suggests a strong association of LDH3 with sputum three positive or severe cases of mycobacterial infection, indicating a likely possibility of using LDH3 as a supporting diagnostic marker in, at least, cases of chronic tuberculosis.
