Infectious Diseases II
Both tests are more specific than the Ξ²-d-glucan test, but they are not as sensitive.
| d. | A meta-analysis that included studies in non-neutropenic critically ill patients found improved |
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sensitivity and specificity of both tests when used in combination. It also demonstrated a varied
sensitivity depending on the Candida spp (C. albicans with the highest and C. parapsilosis with
the lowest).
Galactomannan
Cell wall component of Aspergillus spp.
Platelia enzyme immunoassay can detect galactomannan in serum or other sterile fluids
(bronchoalveolar lavage) within 4 hours.
Variable sensitivity and specificity, with generally better positive and negative predictive values
for the detection of Aspergillus in the patient population with hematologic malignancies than in the
solid organ transplant (SOT) population
| d. | False positives can occur with the simultaneous administration of certain Ξ²-lactam antibiotics |
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(piperacillin/tazobactam, amoxicillin/clavulanic acid) or the presence of other invasive mycoses
(Penicillium, histoplasmosis, blastomycosis).
PCR
An FDA-approved assay is available for detecting Candida spp. only.
This test allows for the early detection of candidemia.
This assay has high sensitivity and specificity and a good negative and positive predictive value.
| d. | Colonization may decrease specificity and using the test too early (e.g., prior to onset of new |
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symptoms) may decrease sensitivity.
An inflammatory biomarker that reflects host response to bacterial infections
such as interleukin (IL)-1b, IL-6, and tumor necrosis factor alpha (TNFΞ±), but it is neutral to cytokines
that are normally released for viral infections such as interferon-Ξ³. Usual concentrations of PCT are
undetectable (less than 0.05 mcg/L). However, on exposure to bacterial toxins, PCT is rapidly released
within 2β4 hours. The plasma half-life of PCT is 24 hours. Concentrations in the literature for infected
patients vary greatly; however, it appears that a higher max concentration of PCT during infection
correlates with a higher incidence of mortality.
PCT is used in many roles, including the diagnosis and prognostication for sepsis. IDSA stewardship
guidelines recommend serial measurements be used in conjunction with other stewardship interventions
to decrease antibiotic use. The Surviving Sepsis Campaign provides a weak recommendation (weak
recommendation, low quality of evidence) for the use of PCT to assist clinicians in the discontinuation
of empiric antibiotics when no evidence of infection is found among patients with sepsis.
For clinical decisions regarding antibiotic use and duration, PCT has been evaluated for antibiotic
initiation, antibiotic cessation, and the combination of both strategies. These strategies assume PCT
availability from an institutional laboratory. If the PCT turnaround time is more than 24 hours, the
effects of minimizing antimicrobial treatment days may be limited.
It is unclear how to interpret PCT levels in certain patient populations; however, PCT use is not precluded
in these populations as long as providers are aware of limitations. According to current evidence, PCT
should be used with caution in the following patient populations:
Chronic kidney disease: Patients with chronic kidney disease have higher baseline levels of PCT.
PCT levels can be elevated among patients during times of noninfectious conditions such as trauma,
surgery, burns, immunomodulator therapy that increases proinflammatory cytokines, cardiogenic
shock, during peritoneal dialysis, and cirrhosis.