Discussion
Often only the urine is tested for antigen and in cases where it is ALQ, it may remain ALQ more than 6-24 months after initiation of treatment, raising the question whether the treatment is working.
In most cases where the urine is ALQ, the serum is quantifiable initially or within a month of treatment [1] providing a better marker for assessing response. As the serum antigen becomes negative or low level (<2 ng/mL), the urine antigen is quantifiable and provides a marker to aid in decisions to stop treatment.
Recommendations
- Send both urine and serum for antigen testing to aid in diagnosis
- If the urine result is ALQ, monitoring the serum until it is negative or <2ng/mL
- Revert to testing urine once serum antigen is negative
- Monitor antigen:
- 3-month intervals during treatment
- 6 and 12 months after stopping treatment
- Any time clinical or imaging findings suggest progression or relapse
Reference List
- Hage CA, Kirsch EJ, Stump TE, et al. Histoplasma Antigen Clearance during Treatment of Histoplasmosis in Patients with AIDS Determined by a Quantitative Antigen Enzyme Immunoassay. Clin Vaccine Immunol 2011 Apr; 18(4):661-6.