Norm of Histoplasmosis Skin Test
Negative as evidenced by no induration and erythema <5 mm in diameter.
Description of Histoplasmosis Skin Test
(See Histoplasmosis serology—Blood.) Skin tests become positive 2–3 weeks after infection and remain positive in 90% of the infected population for life.
Professional Considerations of Histoplasmosis Skin Test
Consent form NOT required.
- Travel history should be included as part of the client's health history to determine exposure to high-incidence endemic areas.
- Obtain an alcohol wipe, a needle, a syringe, and histoplasmin—an antigen prepared from culture (usually commercially prepared).
- Histoplasmin is injected intradermally.
- Record the location of the injection for reading.
- The injection should follow a blood draw for serum titer.
- Read the test in 24–48 hours. An area of erythema and induration of >5-mm diameter is indicative of a positive reaction.
Client and Family Teaching
- See Histoplasmosis serology—Blood.
Factors That Affect Results
- Test may be falsely negative in 50% of people with disseminated histoplasmosis and 10% of people with cavitary histoplasmosis.
- False-negative results may occur because of depressed immunologic status (not in HIV clients) or steroid therapy.
- False-positive results may occur in people with blastomycosis (30%) or coccidioidomycosis (40%).
- Acutely ill clients may not have a positive skin reaction.
- This test is not recommended because of the difficult interpretation and because it may cause the serology test to be falsely positive.