Zinc deficiency may affect TB test results
doi:10.1038/nindia.2014.3 Published online 17 January 2014
Micronutrient deficiency, especially that of zinc, may influence the results of a common children's tuberculosis diagnostic test (QuantiFERON-TB Gold In-Tube test or QFT), new research suggests1 . The researchers say QFT should be used cautiously for diagnosing TB considering the high prevalence of zinc deficiency in developing countries.
There's very little data on the performance of QFT and tuberculin skin test (TST) in micronutrient-deficient children with active TB from high burden countries. The researchers set out to evaluate this among 362 children with intrathoracic tuberculosis. The children underwent TST, QFT, gastric lavages and induced sputum examination for AFB (Acid-Fast Bacilli) smear and culture. Zinc, copper, ferritin and vitamin D were measured on stored serum samples.
Microbiological confirmation of tuberculosis was obtained in 128 patients. TST and QFT were positive in 337 (93%) and 297 (82%) children, respectively. Performance of both the tests was unaffected by weight-for-age and height-for-age 'z-scores' or by serum copper levels. TST was not affected by serum zinc and ferritin levels.
Children with negative QFT results had lower mean serum zinc level and higher ferritin levels as compared to those with positive test results. Higher proportion of children with positive TST were vitamin D deficient/insufficient.
The researchers, therefore, advocate caution in the use of QFT as a diagnostic test in populations with zinc deficiency.