Diagnostic value of C-reactive protein, IgG, and IgA for detection of pulmonary tuberculosis: a case-control study from Eastern China

Background: Tuberculosis control is currently hampered by inadequate diagnostic tools and point-of-care diagnostics are urgently needed. Recent work has highlighted C-reactive protein (CRP) as a potential supplementary tool however its reliability is still unclear. Methods: We performed an age- and sex-matched case-control study in Jiangsu province including pulmonary tuberculosis and healthy controls. We used Wilcoxon rank sum tests to compare CRP, IgG, and IgA values between cases and controls. We estimated sensitivity, specificity, and the positive (+LR) and negative (−LR) likelihood ratio of CRP for pulmonary tuberculosis diagnosis, bacteriologically negative tuberculosis, bacteriologically positive tuberculosis, and healthy controls for different CRP cut-off points. We constructed receiver operating characteristic (ROC) curves to compare diagnostic accuracy of CRP alone or combined with IgG and IgA. Results: In all, 264 participants, 132 cases and controls, were enrolled. We found statistically higher values between cases and controls for both CRP (P<0.0001) and IgG (P=0.006), respectively. With the CRP cut-off points set as 5 mg/L, the values of +LR and −LR were 4.25 and 0.80 in bacteriological positive group. When CRP >8 mg/L, the sensitivity and specificity for pulmonary tuberculosis group and healthy population group were 12.50% and 95.31%, respectively. The diagnostic performance was poor for CRP alone (area under the curve, 0.63; 95% CI, 0.59–0.69), CRP combined with IgG (0.69; 95% CI, 0.63–0.74), CRP combined with both IgG and IgA (0.69; 95% CI, 0.63–0.74) for pulmonary tuberculosis. For bacteriologically-negative tuberculosis, CRP combined with IgG and/or IgA increased diagnostic accuracy compared with CRP alone (P<0.05). Conclusions: In a matched case-control study from Eastern China, CRP demonstrated limited diagnostic value, even when combined with IgG and IgA, in the diagnosis of pulmonary tuberculosis.