Phosphate/creatinine clearance ratio

B. The measurement of the phosphate/creatinine clearance ratio (Cp/Cc.r) from the phosphate and creatinine concentrations in an untimed urine sample and simultaneous blood sample (N5). Tubular reabsorption of phosphate (TRP) can be derived from this figure (TRP = 1 — Cp/Ccr) and has been widely used as a measure of parathyroid activity (C7, R5, T5). Its normal range is reported as 78-90 %. The authors do not make any correction for plasma phosphate concentration. 

C. The measurement of the phosphate excretion index (Nil). Since the phosphate/creatinine clearance ratio is normally directly related in a known manner to plasma phosphate concentration (MIO), the observed Cp/Ccr in any given case can be compared with the normal mean value at the same plasma concentration. The difference is called the Phosphate Excretion Index (PEI) and its normal range is —0.09 to +0.09. The values in hyperparathyroid cases usually lie above the upper normal limit and in hypoparathyroid cases below the lower limit (Nil) (Fig. 10). 

D. Phosphate reabsorption per 100 ml of glomerular filtrate. If the plasma phosphate concentration is multiplied by the phosphate/creatinine clearance ratio, an approximate figure is obtained for the amoimt of phosphate reabsorbed per 100 ml of glomerular filtrate (T7). The normal range of this value is approximately 2-4mg/100ml filtrate (Nil). 

The ratio of the phosphate clearance (CJ to the creatinine clearance (Ccr) gives an indication of the proportion of phosphate filtered at the glomerulus which has been reabsorbed by the renal tubules (a process in which parathyroid hormone is involved). In order to allow for fluctuations in the level of serum phosphate, the phosphate excretion index (PEI) was devised and this is given by the formula ... 

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