Index of Stimulation and TNFα Measurements Used for laboratory Diagnosis of Latent Tuberculosis as a New Principle

A new principle of a method for the laboratory diagnosis of latent Mycobacterium tuberculosis infection (LBTI) compared to the QuantiFERON (QFT) test is presented. The new elements, the calculation and introduction of an Index of Stimulation (IS) were based on the measurements of tumour necrosis-α (TNF-α) release in whole human blood stimulated by the peptides (TB-P) derived from Mycobacterium tuberculosis (Mtb) related proteins and Purified Protein Derivative (PPD). The amount of TNF-α was determined by ELISA. The calculation of IS values was carried by the formula: TNF- α(pg/ml)TB-P/ TNF-α(pg/ml)PPD. The populations studied consisted of a) 15 healthcare workers dealing with Mtb- infected patients (HCWTB); b) 14 healthcare workers not being exposed to Mtb patients (HCW-C) as controls. The diagnosis of LTBI was established if IS was higher than 1.50. In the HCW-TB group the number of LTBI was 6/15 by the new method and 9/15 by QFT. Tested clinically, the number of false-positive results by QFT was 3/9. All members of HCW-C group were LTBI negative by both methods. This new assay did not result in any false positive reactions. Although these results are still preliminary data derived from few patients. However, the theoretical novelties in the principle of method: the calculation of IS from the TNF-α-TB-P/ TNF-α –PPD values can mean a progress in the individual laboratory diagnosis of LTBI in further studies. Key words: Latent tuberculosis; QuantiFERON-TB; tumour necrosis factor –α; TNF-α- IS