Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1352 page)

   Culture of multiple specimens from different infected tissues may improve detection.

   Blood cultures are recommended for evaluation of patients with suspected tularemia.

   Serologic testing is recommended for diagnosis in patients with suspected tularemia.

   Interpretation

   
Expected results:
Negative. After the acute phase of infection, cultures may become negative. Tularemia cannot be confidently ruled out by negative cultures.

   
Positive:
Isolation of
F
.
tularensis
is diagnostic of tularemia. Tularemia is a reportable disease; positive cultures must be reported to the local department of health.

   Limitations

   Because
F
.
tularensis
organisms are tiny and faintly staining, direct detection by Gram stain of clinical specimens is uncommon. Cultures late in infection may be negative. Serologic diagnosis may be helpful in patients with disease consistent with tularemia, but negative cultures.

   
Common pitfalls:

   The diagnosis of tularemia may not be entertained until after the most acute phase of illness, a time when cultures are less likely to be positive.

   Clinicians may fail to request specific cultures for tularemia or alert the laboratory of their clinical suspicion.

FUNGAL ANTIGEN, BETA-
D
-GLUCAN

   Definition

   (1-3)-β-
D
-glucan (BG) is a cell wall component of most fungi, except
Zygomycetes
and
Cryptococcus
species. BG has been used as a biomarker for invasive fungal infections (IFI), including candidemia and
Pneumocystis
pneumonia; an FDA-approved test for quantitative BG detection is available. In patients with ILI or
Pneumocystis
pneumonia, significant levels of BG may be detected in the serum significantly earlier than clinical signs and symptoms or detection of infection by laboratory or imaging studies. Decreasing BG levels have been associated with treatment success.