Sieving coefficient

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Sieving coefficient (S) measures how well a substance balances between two streams during contact. It is the ratio of the average concentration in the receiving stream to the average concentration in the donating stream: S = Cr / Cd, where Cr is the receiving stream’s average concentration (before and after contact) and Cd is the donating stream’s average concentration (before and after contact). If S = 1, the two streams reach the same concentration (complete equilibration). S > 1 would require external energy and is not normally possible; S < 1 means the streams have not fully equilibrated. The contact time between streams affects S—the longer they interact, the closer S gets to 1. In kidney physiology, the glomerular sieving coefficient (GSC) is defined as GSC = clearance / ultrafiltration rate.