Clinical utility of serum galactomannan test

Dr. Feros

1. Clinical utility of Serum Galactomannan test Dr.Mohammed Feros Post graduate

2. Introduction Galactomannans – polysaccharides consisting of mannose backbone with galactose side groups. Often used in food products to increase viscosity of water phase. Component of the cell wall of mold Aspergillus and is released during its growth. Detection in blood – diagnose invasive aspergillosis in human. Most useful in patients who have had stem cell transplants.

3. Detection Enzyme linked assay – used for detection of Aspergillus galactomannan antigen (monoclonal antibody). Test is primarily used for : 1) Monitoring immunosuppressed patients for development of galactomannan antigenemia. 2) Diagnosis of suspected case of invasive aspergillosis.

4. GMI(Galactomannan Index) – 0.5 or higher in US & 1-1.5 or higher elsewhere is considered positive. Positive results should be considered in conjunction with – i ) Microbiologic culture i i) Radiologic evidence i ii) Histologic Examination of biopsy specimen i v) Reproducibility in new specimen (retesting new aliquot of specimen )

5. Negative results does not rule out diagnosis. Repeated testing if IA is suspected. False positivity can occur due to: a) Concomitant administration of some antibiotics ( penicillium spp ) b ) Infection from other than aspergillus (histoplasmosis and other endemic mycosis) c) Administration of fluids containing sodium gluconate or citric acid such as transfusion platelets, parenteral nutrition or plasmalyte .

6. Monitoring for Invasive Aspergillosis Indication for test is in high risk patients:- 1) Prolonged neutropenia 2) Allogenic SCT Criteria for positivity: i ) 2 consecutive serum specimen with GMI >0.5 i i) Repeat test before implementing therapy for invasive aspergillosis

7. Maertens et al – requiring consecutive results with GMI > 0.5 or higher as criteria as positivity reported – Sensitivity 100% & Specificity 97.5% Meta-analysis noted sensitivity of 79% & specificity of 86% with an overall accuracy of 89%.

8. Evaluation of suspected Pulmonary IA Halo-sign is suggestive of IA – but sensitivity is 25%. Air crescent sign/cavities/ nodules did not differentiate IA from bacterial infection. Cytology or culture of BAL were positive in less than ¼ patient underwent bronchoscopy. Sensitivity can be improved – BAL in EIA method

9. SCT patients Sensitivity of 61% & Specificity 98% was reported. Solid organ transplants Sensitivity ranged from 67 – 100 % & Specificity 98-100% .

10. THANK YOU