A healthy 24-year-old man cleaned the gutters on his 16-year-old fishing cabin on a lake in Wisconsin. He presented for medical evaluation 12 days later for symptoms of fever, malaise and cough of 5 days’ duration.
Is there a reason to test both urine and serum for Histoplasma antigen ?
Physical findings included a temperature of 100.5°F and the spleen tip that was palpable on examination. Chest radiograph showed right hilar and anterior mediastinal lymphadenopathy and miliary infiltrates. Histoplasmosis was suspected and urine was sent to MiraVista Diagnostics for Histoplasma antigen, which was negative.
Does a negative urine antigen exclude pulmonary histoplasmosis?
Most clinicians only order antigen on urine and do not recognize the value of testing serum. Analysis of the results obtained in 158 patients at one institution between 2014-2019 in whom both urine and serum were tested and at least one was positive are presented in the table.
|Result||Urine Positive||Urine Negative|
|Serum negative||8%||Not determined|
16% of cases may have been missed if only urine was tested: serum should also be tested for antigen. A study of patients with heavy exposure acute pulmonary histoplasmosis found that antigen was negative in urine but positive in serum in 46% of patients . Testing for anti-Histoplasma IgG and IgM antibodies further increased the sensitivity for diagnosis. IgG antibodies were detected in 88%, IgM in 68 %, and IgG and/or IgM in 89% of patients and combined antigen and antibody testing increased sensitivity to 96% .
1. Send both urine and serum for antigen and test for both
2. Test the serum for anti-Histoplasma IgG and IgM antibodies and FID antibodies