Samples of venous and capillary blood were collected simultaneously from healthy adults to assess the accuracy of platelet counts in capillary blood as determined by an automated particle counter. The difference between the mean venous blood platelet count (248,300) and the mean capillary blood count (215,500) was highly significant (P less than .001). For 24% (7/29) of the subjects, the capillary blood platelet count underestimated the venous blood count by greater than or equal to 25%, with three subjects erroneously classified as thrombocytopenic. A heterogeneous group of thrombocytopenic patients showed a similar difference in mean platelet counts (venous blood: 72,500/microliter; capillary blood: 65,400/microliter; P = 0.01). In most clinical situations, capillary blood platelet counts were adequate for patient evaluation; however, when an accurate platelet count is necessary, venous blood should be used.

The Coulter Model S provides an accurate measurement of total hemoglobin (Hb) content in peripheral blood even when elevated levels of carboxyhemoglobin (HbCO) are present. Commercial standards and diluents for spectrophotometric determinations of cyanmethemoglobin (HiCN) are variable in quality. All diluents studied produce turbidity in some samples, and this may explain why manual Hb determinations tend to be higher than hemoglobin measurement on the Coulter S. The most reliable diluent was the reagent described by Van Kampen and Zijlstra. Its reliability is enhanced by centrifugation of sample in diluent. The use of a narrow-band-pass spectrophotometer for routine HiCN determinations in a clinical laboratory is not recommended because of its sensitivity to turbidity and HbCO.

No abstract

No abstract