Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1324 page)

   
Positive result:
Disease caused by specific parasite identified.

   Limitations

   Low level of parasitemia may require the examination of multiple specimens for detection. Examination of smears prepared from buffy coat preparations may improve the sensitivity of detection for some parasites, like microfilaria and trypanosomes. The efficient detection of microfilaria requires specimen collection during the specific hours when circulation of the parasite is expected.

   
Common pitfalls:
Include the collection of too few specimens for examination.

   Other Considerations

   In effectively treated patients, the level of parasitemia should drop very quickly. In patients with drug-resistant parasites, the level may remain stable, or even increase.

Suggested Readings

Garcia LS.
Diagnostic Parasitology
, 5th ed. Washington, DC: ASM Press; 2007.

NCCLS document M15-A.
Laboratory Diagnosis of Blood-borne Parasitic Diseases
; Approved Guideline. 2000. Clinical and Laboratory Standards Institute.

BODY FLUID CULTURE

   Definition

   Sterile fluid-filled spaces are present at a number of anatomic sites and are subject to infection. Examples of sterile fluids include peritoneal, pleural, pericardial, and synovial/joint fluid. Infections associated with CSF are life threatening and associated with a different etiology of bacterial pathogens, so these cultures are typically processed differently than other sterile fluids. Urine is also processed with different culture techniques because of its connection with the external environment, via the urethra, and pathogenesis of infection. A broad etiology of bacterial pathogens may cause infections of sterile sites, and culture methods are optimized for recovery of organisms present in low concentrations.

   Use

   Collect sterile fluid cultures from sites associated with signs and symptoms of inflammation, including redness, swelling, pain, heat, fluid accumulation, and pus formation.

   
Method:
Supportive and enriched solid agar (SBA and chocolate agar) and broth media (blood culture media) are typically inoculated; selective/differential agar media, such as MacConkey agar (gram-negative bacilli), CNA, or phenylethyl alcohol agar (gram-positive organisms), should be inoculated for specimens likely to show polymicrobial infection (e.g., peritonitis) or contamination by endogenous flora (e.g., cul-de-sac aspirates). Anaerobic media should be inoculated if there is a significant possibility of anaerobic pathogens. If infection with an uncommon, fastidious pathogen is suspected, the laboratory should be informed so that special cultures may be inoculated.

   
Turnaround time:
Cultures are incubated for up to 7 days. Additional time is required for isolation, identification, susceptibility testing, and further characterization, as needed.