Sensitivity of hemozoin detection by automated flow cytometry in non- and semi-immune malaria patients.
BACKGROUND
Cell-Dyn automated blood cell analyzers use laser flow cytometry technology, allowing detection of malaria pigment (hemozoin) in monocytes. We evaluated the value of such an instrument to diagnose malaria in febrile travelers returning to Berlin, Germany, the relation between the instrument's performance and the patients' immune status, and the capacity to increase its sensitivity.


METHODS
Malaria diagnosis was routinely established by thick-film microscopy. The patients' immune status was determined by an indirect fluorescent antibody test. Hemozoin detection was performed with a Cell-Dyn 3000. To assess the capacity for sensitivity increase, the relative frequencies of pigment-containing monocytes were determined for a subgroup of patients with the Cell-Dyn 3000 in comparison with a flow cytometer specifically adapted to rare-event analysis.


RESULTS
Of 403 patients screened microscopically, 107 had malaria. Overall sensitivity with the Cell-Dyn 3000 reached 48.6% (73.7% in semi-immune and 28.6% in nonimmune individuals; P < 0.0001). Specificity was 96.2%. The detection limit was at a relative concentration of 2 x 10(-4) pigment-containing monocytes (PCMs). By employing rare-event flow cytometry, the detection limit decreased to 3.25 x 10(-5), thus yielding a considerably increased sensitivity for the subgroup studied.


CONCLUSIONS
The correlation between immune status and relative concentration of PCMs explains the failure of the routine instrument for nonimmune patients and its significantly higher sensitivity for semi-immune individuals. The technique can be significantly improved by rare-event flow cytometry.
Grobusch
Martin P
MP
Medizinische Klinik (Infektiologie), Charité/Campus Virchow-Klinikum, Humboldt-Universität, Berlin, Germany. martin.grobusch@uni-tuebingen.de
Hänscheid
Thomas
T
Krämer
Benedikt
B
Neukammer
Jörg
J
May
Jürgen
J
Seybold
Joachim
J
Kun
Jürgen F J
JF
Suttorp
Norbert
N
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D002469:Cell Separation; D002648:Child; D002675:Child, Preschool; D005260:Female; D005434:Flow Cytometry / Q000295:instrumentation / Q000379:methods; D019084:Fluorescent Antibody Technique, Indirect; D006420:Hemeproteins / Q000032:analysis*; D006801:Humans; D007223:Infant; D008288:Malaria / Q000175:diagnosis* / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D009000:Monocytes / Q000737:chemistry*; D012680:Sensitivity and Specificity
D006420:Hemeproteins; C020753:hemozoin