In severe falciparum malaria there is a microvascular obstruction due to sequestration of parasitized erythrocytes. In addition, red blood cell deformability is significantly reduced in severe malaria, which is due mainly to changes in unparasitized erythrocytes. Red cell deformability is particularly low in fatal cases and can be used to identify those patients at significant risk on admission to the hospital.
Patient Populations: Thai natives >= 14 years of age, nonpregnant and without a history of previous antimalarial drug treatment within 24 hours of admission.
Test Method and Conditions:
(1) Technique: ektacytometry
(2) Instrument: laser-assisted optical rotational cell analyzer
(3) Shear stress applied: 1.7 Pascal (approximates the shear stress encountered in vivo in the venules)
(4) The unit of deformability is the elongation index (EI).
Interpretation:
• A severely reduced red cell deformability, as indicated by a red blood cell elongation index < 0.21 on admission to the hospital, predicts a fatal outcome with a sensitivity of 100% and specificity of 88%. Patients with fatal outcomes tended to have EIs in the range of 0.16 to 0.20.
• Healthy controls had EI of 0.25 to 0.32.
• Patients with uncomplicated malaria had an EI from 0.22 to 0.32
• Patients with severe but nonfatal malaria usually had an EI in the range of 0.22 to 0.31, with a few showing an EI as low as 0.18.
