Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1323 page)

   Routine blood cultures are optimized for detection of the pathogens most frequently associated with BSIs. Clinically relevant BSIs may be associated with pathogens for which special blood cultures are required (e.g., mycobacteria, dimorphic fungi, fastidious bacteria).

   
Common pitfalls:

   Decreased sensitivity because of such factors as a low volume of blood inoculated into blood culture media. Decreased specificity because of contamination due to poor preparation of collection site.

Suggested Readings

CLSI.
Principles and Procedures for Blood Cultures; Approved Guideline
. CLSI document M47-A. Wayne, PA: Clinical and Laboratory Standards Institute; 2007.

Katidis AG, et al.
Pediatric Infect Dis J.
1996;15:615–620.

Yakoe DS, Anderson J, Chambers R, et al. Simplified surveillance for nosocomial bloodstream infections.
Inf Control Hosp Epidemiol.
1998;19:657–660.

BLOOD PARASITE EXAMINATION

   Definition and Use

   This test is used to detect parasites circulating in peripheral blood. It should be ordered in patients when infection caused by
Plasmodium
species (malaria),
Babesia
species (babesiosis),
Trypanosoma
species (sleeping sickness, Chagas disease), or certain microfilaria species or systemic infection with
Leishmania
species is suspected. Thin and thick blood smears are prepared from free-flowing capillary blood or EDTA-anticoagulated blood. Smears are inspected after staining with Giemsa, Wright, or Wright-Giemsa stain. For positive smears, the level of parasitemia should be determined for each specimen.

   
Turnaround time:

   Preliminary examination should be performed “STAT” if malaria is suspected (turnaround time <4 hours). Final report for positive smears: <24 hours.

   Special Collection and Transport Instructions

   Preparation of smears at the bedside, from free-flowing capillary blood if possible, yields the best morphology. Alternatively, EDTA-anticoagulated blood may be collected. For microfilariae, the diurnal circulation of some species must be taken into account in timing specimen collection (
Loa loa
: 10
AM
–2
PM
;
Wuchereria
or
Brugia
species: 8
PM
– 4
AM
). Transport specimens to the laboratory and prepare smears as soon as possible. In general, collect specimens on each of 3 successive days. Collect specimens every 6–8 hours (until positive) for optimal detection in suspected cases. Blood should be examined in treated patients after 24, 48, and 72 hours to determine effectiveness of therapy.

   Interpretation

   
Expected results:
Negative. Sensitive detection of parasitemia may require the examination of several specimens, as recommended above.