Standardising erythrocyte sedimentation rate with stable controls

In 1993 the International Committee for Standardisation in Haematology (ICSH) met to consider how erythrocyte sedimentation rate (ESR) should best be done and how to ensure good agreement between laboratories. At that time no stable ESR controls were available so the ICSH settled on describing, in great detail, a Reference method and a Standard method.1 Both involve taking whole blood and either diluting with autologous plasma to lower the haematocrit or using whole blood with a low haematocrit. This is then placed in a vertical open Westergren pipette (20-cm long, 2.55-mm bore), with the length of clear plasma above the red cell meniscus measured (mm) after one hour.

Sedimentation in practice
The ICSH recognised that neither method would prove practical in routine use, so it stipulated that any other ESR method that showed good agreement with either the Reference or Standard method could be used routinely, and could be termed a Selected method. In practice, the majority of laboratories use the Westergren method, which circumvents the haematocrit ‘problem’ by using whole blood diluted (I in 4) with isotonic sodium citrate, set up in a narrow-bore Westergren pipette. Again, the length of clear liquid above the red cell interface is measured after one hour to give the ESR reading. This has been shown to correlate well with the Standard method.

A variation of this method is to use the same citrated sample, in a shorter and wider bore tube to facilitate mixing. These shorter tubes give much lower values for the red cell sedimentation, but this can be corrected to give a true ESR. However, it is unlikely that any haematology laboratory in the UK checks their ESR method against either of the two ICSH methods regularly, if ever, as recommended, and no one is using any of these methods in order to make inter-laboratory comparisons.