ESR stands for Erythrocyte (red blood cell)Sedimentation Rate.
In the presence of some inflammatory proteins (but probably not all)the red cells aggregate together into lumps and then sediment out of "solution" faster.
The thoroughly mixed anticoagulated blood sample is placed in a glass or plastic tube with a standard bore and the red cells allowed to settle out over a period of 1 hour. This gives a result of xx mm/hour. I'm not sure if America uses metric measurements?
Although a very old and non-specific test it still remains a very good marker and a crude guage of the extent of an inflammtory process.

I would guess that if the inflammtory proteins for some reason did not cause the cross linking of the red cells into aggregates then the ESR would be normal inspite of the inflammatory process and then CRP (C Reactive Protien) might be a better indicator of inflammation.

The only time an ESR is considered urgent is in the case of Temporal Arteritis (that's arteritis and not arthritis).

Cheers DEP

Dx Oct 2006 B27+ undifferentiated spondlyarthropathy (uSpA) with mild sebhorrhoeic dermatitis and mild Inflammatory Bowel Disease (IBD) controlled by NSD since 2007.