Of 382 patients undergoing prostatectomy in Oxford in 1985 the prevalence of renal impairment (defined as plasma urea > 14 mmol/l or plasma creatinine > 200 mumol/l) was 8%; prostatectomy patients had significantly higher plasma ureas than age-matched patients undergoing herniorrhaphy and cholecystectomy in the same hospitals in the same year. A review of the case records of men with renal impairment showed that case history could not predict renal impairment. Although few case notes gave follow-up information, it was evident from the information available that recovery of renal function after prostatectomy did not occur invariably. Renal impairment in men undergoing prostatectomy represents substantial and unrecognised morbidity.

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Recent substantial increases in clinical blood folate concentrations are noted. Since red cell folates (RCF) are calculated from whole blood folates (WBF) by subtraction of the endogenous serum folate (SF) component, the reporting of clinical RCF results may be delayed because an ever increasing proportion (15%) of diagnostic SF levels are high (> 20 ng/ml) and need a repeat analysis. We evaluated 'plasma replacement' as a simple preanalytical procedure in which endogenous blood plasma is removed from red cells by washing and substituted with 'low-folate' plasma (serum) as an alternative conjugase (gamma-glutamyl carboxypeptidase) source for folate polyglutamate hydrolysis. Washed and conventional RCF assays compared well after both manual (n = 115, r = 0.98, y = 1x + 1.26) and automated washing of red cells (n = 170, r = 0.96, y = 0.96x - 0.73 ng/ml) and were not significantly different. The interassay reproducibility of folate results from washed blood samples was good (CV = < 6%). This novel 'plasma replacement' step halves the cost of a valid RCF assay by eliminating the need for endogenous SF analysis, and it expedites the reporting of clinical results.

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