Reply to 'low-positive Histoplasma antigen results in the MVista assay should not be assumed to be false positive'

摘要

We read with interest the letter to the editor from Hage and Wheat regarding our recent publication entitled "Clinical significance of low-positive Histoplasma urine antigen results" and consider that a few points require clarification (1,2).Hage and Wheat comment that 12 of 57 patients had a MiraVista (MVista) Histoplasma capsulatum urine antigen (UAg) result below the limit of quantification (BLQ), which was considered falsely positive in our publication. Our study, however, focused only on the clinical utility of "positive, BLQ" MVista results from patients without a history of histoplasmosis, and the medical charts of only this subgroup of individuals (n = 25) were reviewed. As noted in our report, of the 57 patients who met the inclusion criteria (i.e., a "positive, BLQ" UAg result), 32 were excluded from analysis because they had a previously positive MVista Histoplasma UAg result and the most recent testing was assumed to have been ordered for monitoring purposes. The medical records of these 32 patients were not reviewed, and therefore, these patients should not be included in the above calculation. This does, however, present an interesting question: what is the clinical significance of persistent, low-level Histoplasma antige-nuria in patients who have completed an appropriate course of antifun-gal therapy who are asymptomatic? The most recent Infectious Diseases Society of America guidelines note that continued low-level antigenuria may not be an adequate reason to prolong treatment in the absence of ongoing clinical disease (3). Additional studies to define the clinical significance of such results are needed.