Tuberculosis Detection May Be Affected by Blood Draw Method

Scientist looking at blood specimen
Scientist looking at blood specimen
Tuberculosis screening results may differ depending on blood draw methods.

Healthcare workers participating in annual tuberculosis screening had differences in interferon (IFN)-γ level depending on blood draw methods, according to study results published in the Annals of the American Thoracic Society.

Whole blood samples from healthcare workers in Texas who had a previous positive tuberculin skin test, a BCG vaccination, or immunosuppression were drawn into 3 QuantiFERON Gold (QFT-G) tubes, 2 QFT-P (Gold Plus) antigen tubes, and a lithium heparin blood tube (QFT-PT). The differences in IFN-γ level measured between methods was evaluated, and agreement was calculated between groups.

Of the 300 study participants with blood drawn, 299 had results from all 3 different methods. Of these 299 participants, 68% were female, 45% identified as Asian, 65% previously had the BCG vaccine, 79% were foreign-born, and 55% had a previous positive tuberculosis skin test. Overall, QFT-G and direct in-tube (QFT-PD) methods had the highest agreements, at 91.3%.

Using a conservative definition with an IFN-γ cutoff of both TB1 and TB2 ≥0.35 IU/mL for a positive QFT-P, 7% of participants with QFT-PD and 9% of participants with QFT-PT had positive results. The median IFN-γ measured in the Nil tube for the disagreeing QFT-PD and QFT-PT results was 0.18 and 0.13 IU/mL, respectively.

“Using the manufacturer’s interpretation for positive results, the overall percent agreement between QFT-G and QFT-P was high, regardless of blood collection method, but lowest between QFT-PD and QFT-PT,” the researchers wrote.

Related Articles

They added, “The option of collecting blood into a single lithium heparin tube prior to blood transfer may be beneficial in lowering the proportion of indeterminate QFT in a clinical setting.”


Agarwal S, Nguyen DT, Lew JD, Graviss EA. Phlebotomy methods may affect QuantiFERON Gold Plus assay results [published online December 5, 2018]Ann Am Thorac Soc. doi:10.1513/AnnalsATS.201804-239RL

This article originally appeared on Pulmonology Advisor