Moxifloxacin and Galactomannan False Positives
Moxifloxacin does not cause false-positive galactomannan test results. The well-documented causes of false-positive galactomannan testing are beta-lactam antibiotics (particularly piperacillin-tazobactam and amoxicillin-clavulanate), enteral nutritional supplements, and certain patient populations, but fluoroquinolones like moxifloxacin are not among them 1, 2, 3.
Known Causes of False-Positive Galactomannan
The primary culprits for false-positive galactomannan results are:
Beta-lactam antibiotics: Piperacillin-tazobactam is the most notorious, but amoxicillin-clavulanate, amoxicillin, ampicillin, and phenoxymethylpenicillin also cause false positives 1, 2, 3. These antibiotics contain galactomannan in their formulations that cross-reacts with the assay 3.
Enteral nutritional supplements: These can cause false-positive results, particularly in patients with intestinal graft-versus-host disease or mucosal barrier injury 4.
Chemotherapy or mucositis: Cross-reactive epitopes from other fungi or bacteria can penetrate the damaged intestinal mucosa and cause false positives 2.
Specific patient populations: Lung transplant recipients have higher false-positive rates (41.7% in one study) due to frequent Aspergillus colonization of airways 5.
Characteristics of Beta-Lactam-Induced False Positives
When beta-lactams cause false-positive galactomannan results 3:
- Antigenemia becomes negative 24-120 hours after stopping the antibiotic 3
- Three kinetic patterns occur: persistent GMI >2.0 (65.7%), GMI 0.5-1.5 (25.7%), or variable GMI (14.3%) 3
- Sampling serum prior to the next beta-lactam dose does not reliably decrease GMI below threshold 3
- Testing suspected antibiotic batches remains the only reliable indicator of possible false positivity 3
Clinical Implications for Immunocompromised Patients
In immunocompromised patients receiving moxifloxacin 6, 1:
- Continue to use galactomannan testing as recommended: Serum galactomannan should be performed at least twice weekly in high-risk patients (strong recommendation) 6, 1
- A cutoff of 1.0 ODI provides optimal diagnostic performance: Sensitivity 79%, specificity 88% 6
- Mold-active antifungal prophylaxis or therapy (not moxifloxacin) significantly reduces galactomannan sensitivity and causes false-negative results 2
Important Caveats
- Serial testing is essential: A single negative galactomannan test does not rule out invasive aspergillosis 1, 2
- If clinical suspicion remains high despite negative serum galactomannan: Proceed to bronchoscopy with BAL for galactomannan testing (sensitivity 84%, specificity 88%) 1
- Combination testing improves accuracy: GM (BAL) combined with beta-D-glucan (serum) shows sensitivity 92%, specificity 93% 1