I am consulting on a patient with end-stage renal disease who recently underwent kidney transplantation. The patient developed a febrile illness, splenomegaly, respiratory distress and miliary pattern on chest x-ray. I suspect histoplasmosis, but the urine antigen was negative. Bronchoscopy was performed and Histoplasma was visualized in and cultured from lavage fluid. Are you aware of patients with severe histoplasmosis whose antigen test is negative?
I have consulted on such patients. The antigen test was not performed at MiraVista. When urine was subsequently tested at MiraVista, it was highly positive, as was serum. Results may be falsely negative when testing is performed at laboratories other than MiraVista, as they use a different assay with different performance characteristics. To rule out false negative results, physicians at institutions that do not send Histoplasma antigen to our facility often send an additional specimen to MiraVista to test in the MVista® Blastomyces antigen assay which is entirely cross-reactive to Histoplasma antigen.
Histoplasmosis is usually asymptomatic or causes mild illness following acute exposure in healthy individuals but may be severe following intense exposure or in immunocompromised patients. Studies from the United States noted 3% mortality in patients with inflammatory disorders treated with biological agents , 5% in patients living with HIV/AIDS (PLHIV)  and 10% in solid organ transplant patients .
MiraVista Histoplasma Antigen Enzyme Immunoassay (MVista Ag EIA)
Results in patients with progressive disseminated histoplasmosis (PDH) are displayed in table 1 . Antigen was detected in the urine in 90%: 92% in PLHIV, 94% with other immunocompromising conditions, 64% in those who are not immunocompromised, and 90% overall.
The MVista Ag EIA was used to assess response to treatment in patients with PDH in an AIDS Clinical Trial Group/Mycoses Study Group (ACTG/MSG) study [5-8]. The MVista Ag EIA was also used for diagnosing relapse .
The MVista Ag EIA is validated for testing multiple body fluids including urine [4, 10], serum [4, 10], bronchoalveolar lavage fluid (BAL) [11, 12] and cerebrospinal fluid (CSF) [13, 14] and complies with CLSI and New York requirements. It is also used for detection of antigen in other sterile body fluids.
Serum and urine testing provides the highest sensitivity for diagnosis. One hundred fifty-eight patients in whom both urine and serum were tested and at least one was positive found urine to be negative in 16% of patients in whom the serum was positive.
Monitoring antigen clearance is used as an aid in deciding when treatment can be discontinued. This is possible because results are highly reproducible, figure 1 . Changes in serum concentration are more informative than urine. Serum concentration may be quantifiable when urine is above the limit of quantification, ALQ (20 ng/mL). If both are >20 ng/mL the urine may remain ALQ for a year or more while the serum declines into the quantifiable range within 1-2 months.
Commercial EIAs. Histoplasma antigen EIAs are also available from some commercial laboratories. Their performance characteristics differ from the MVD EIA, table 2.
MiraVista Histoplasma IgG and IgM Antibody EIA
The MVD Histoplasma antibody EIA is more sensitive (89%) than immunodiffusion (56%) or complement fixation (73%) . Combined MiraVista IgG and IgM antibody and antigen detection in CSF was the most sensitive (98%) method for diagnosing Histoplasma meningitis and the specificity was 91%, table 3 .
Turnaround time (TAT). Another important feature of the MVD antigen and antibody EIAs is rapid TAT. Antigen testing is performed twice daily Tuesday through Friday and once daily Monday and Saturday and results are reported the day the specimen is received in 91%, within two days in 96%, and three days in 99%. Antibody testing is performed Monday and Wednesday through Saturday.
Recommendations for Diagnosis
Monitoring Treatment. Monitor monthly during the first 3 months and then every 3-4 months during the first year of treatment. Continue treatment until antigen is no longer detected in the urine and serum . Determine the antigen concentration at other times if there is concern about treatment failure or relapse.
Table 1. Diagnostic tests in progressive disseminated histoplasmosis.
(N = 38)
(N = 62)
(N = 11)
(N = 111)
|Culture4||34/38 (89.5%)||57/61 (93.4%)||7/8 (87.5%)||98/107 (91.6%)|
|Pathology4||18/23 (78.3%)||32/38 (84.2%)||8/8 (100%)||56/68 (82.3%)|
|Antigen5||35/38 (92.1%)||58/62 (93.5%)||7/11 (63.6%)||100/111 (90.1%)|
1Patients living with HIV, 2other immunocompromise, 3non-immunocompromise, 4proven, 5probable
Table 2. Comparison of MiraVista Histoplasma antigen EIA with other commercial tests.
|Parameter||MVD antigen EIA||Commercial EIAs|
|Reproducibility, figure 1||Excellent ||Unknown|
|Monitoring treatment||Yes ||Unknown|
|Diagnosis relapse or treatment failure||Yes ||PLHIV Unknown|
|Sensitivity PDH||92%  to 100% ||92% |
|Specificity PDH||99% [4, 15]||51% |
|Specimens tested||Urine, Serum, BALF, CSF, OBF**||Unknown|
|Limit of detection||0.2 ng/mL||Unknown|
|Turnaround time||1 day 91%, 2 days 96%, 3 days 99%||Unknown|
|Expert clinical consultation||Yes||Unknown|
|*serum usually quantifiable, **other body fluids|
Table 3. Combined antigen and antibody detection for diagnosis of Histoplasma meningitis .
|Antigen||78% (39/50)||97% (140/145)|
|IgG or IgM antibody||82% (37/45)||93% (142/153)|
|Antigen or antibody||98% (48/49)||91% (139/153)|
|Culture||19% (9/47)||100% (119/119)|
Figure 1 Reproducibility: urine tested in the same or different assays .