Indeterminate QuantiFERON® -TB Gold results in a public health clinic setting

Abstract

Public chest clinics, New York City. To evaluate the association between patient characteristics and indeterminate QuantiFERON ® TB Gold (QFT-G) results and describe follow-up testing. Retrospective cross-sectional multivariate logistic regression analyses of patients receiving QFT-G from October 2006 to June 2008. Analyses were performed separately depending on whether the indeterminate result was due to positive (low mitogen) or negative (high nil) control failure. Of 28 864 individuals tested, 2058 (7%) tested positive, 26 284 (91%) negative, and 522 (2%) were indeterminate (low mitogen, n = 264; high nil, n = 258). Low mitogen results were more frequent among those aged < 10 years (OR(adj) 3.7, 95%CI 2.4-5.9), females (OR(adj) 1.4, 95%CI 1.1-1.8), Asians (OR(adj) 2.1, 95%CI 1.3-3.4) and the US-born (OR(adj) 1.9, 95%CI 1.4-2.6) and less frequent among Hispanics (OR(adj) 0.6, 95%CI 0.4-1.0). High nil results were more frequent among Hispanics (OR(adj) 1.7, 95%CI 1.0-2.8) and less frequent among the US-born (OR(adj) 0.6, 95%CI 0.5- 0.8). Among patients who received a repeat QFT-G (n = 137), 4% tested positive, 64% negative and 32% had a second indeterminate result, always of the same type. Age, race/ethnicity and sex were associated with indeterminate QFT-G results. Most follow-up tests were negative, although a modest proportion were repeatedly indeterminate. Further studies evaluating the mechanisms of QFT-G indeterminate results are needed.