A bronchoalveolar lavage sample from a neutropenic leukemia patient is tested for Aspergillus galactomannan by ELISA. The optical density of the test sample is 1.2, the cutoff control is 0.6, and the positive control is 2.0. The calculated galactomannan index is 2.0. According to the FDA-approved cutoff, what does this result indicate?

• A Negative; GM index <0.5
• B Positive; GM index ≥0.5 in BAL fluid ✓
• C Borderline; GM index 0.5-0.7, repeat testing recommended
• D Positive; GM index ≥1.0 in BAL fluid

Explanation

The GM index is calculated as test sample OD divided by cutoff control OD (1.2/0.6 = 2.0). For BAL fluid, the FDA-approved Bio-Rad Platelia Aspergillus ELISA cutoff for positivity is an index ≥0.5. For serum, the cutoff is also ≥0.5 (updated from the earlier 0.5 single-test threshold). The ≥1.0 cutoff (distractor D) is sometimes used in European EORTC/MSGERC guidelines for serum but not the FDA BAL cutoff. The index of 2.0 is clearly positive.

Reference: Murray Rosenthal Pfaller Medical Microbiology, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.