Quantification of neutrophil and monocyte CD64 expression: a predictive biomarker for active tuberculosis.

SETTING

QuantiFERON TB assay (QFT) is used to screen tuberculosis (TB) infection, but it cannot distinguish active TB from latent TB infection (LTBI).

OBJECTIVE

To evaluate the quantitative expression of the high-affinity FCgamma receptor I (CD64) on neutrophils (NE) and monocytes (MO) in peripheral blood using flow cytometry, measured in antibody binding capacity (ABC) units as a predictive biomarker of TB.

DESIGN

Fifty-two patients were enrolled (45 QFT-positive and 7 QFT-indeterminate). Cultures and molecular analyses were performed.

RESULTS

Of the 45 QFT-positive patients, 29 were culture-positive (active TB) and 16 were negative (LTBI). The median NE CD64 ABC and MO CD64 ABC expression was significantly higher (P < 0.001) in culture-positive patients. The NE CD64 and MO CD64 area under the receiver operating characteristic curve values were respectively 0.948 (95%CI 0.838-0.992) and 0.989 (0.901-1.000). By setting the cut-off NE CD64 value at >2400 ABC or MO CD64 value >25 800 the assay sensitivity increased to 95.5% with 100% specificity and 100% positive predictive value. In the QFT-indeterminate group, five culture-positive cases had NE CD64 >2400 ABC or MO CD64 value >25 800; two culture-negative cases had lower values.

CONCLUSION

The CD64 quantitative expression on peripheral blood cells may be used as a predictive biomarker for active TB.