Dilution principle

When the Starrsed ST is operating in the EDTA mode, the blood sample is diluted with sodium citrate during the aspiration process. On the Starrsed ST, the dilution is achieved through a mechanical link between the syringe on the diluter and the pipette piston. The dilution ratio is 4 volumes blood + 1 volume sodium citrate diluent; accuracy ±3%.

The citrate dilution (4:1) takes place to reduce the influence of HCt (Hematocrit) on the sedimentation process. Dilution brings the Hct level from 0.45 (considered as a normal level) to 0.36. The ICSH (1993) recommended the use of EDTA samples with a Hct of 0.35 or less. Dilution errors up to 25% results in a 5% variation in Hct of the prepared sample. This is within the natural variation in Hct between individual humans and will not have significant influence on the accuracy of the ESR measurement.