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zeta sedimentation ratio, ZSR
The ratio of the zetacrit to the hematocrit, normally 0.41 to 0.54 (41 to 54%); used as an indicator of the red blood cell sedimentation rate.

It is a sensitive indicator of the erythrocyte sedimentation rate (ESR) and is unaffected by anemia, which tends to elevate the ESR.