The effect of bile salts on the esterolytic assay of trypsin.

A bile salt mixture and pure sodium taurocholate were each shown to increase the esterolytic activity of trypsin in aqueous solution and in intestinal juice. rho-Toluene-sulphonyl-L-arginine methyl ester (TAME) was used as a substrate, and both a spectrophotometric and a potentiometric assay system were used. The maximal potentiation of the esterolytic activity of trypsin by bile salts was about 1.6 to 2.2 times the activity without bile salts (depending on the assay conditions and whether the trypsin was in aqueous solution or intestinal juice). The proteolytic activity of trypsin was decreased by the addition of bile salts. It seemed likely, therefore, that the potentiating effect of bile salts on trypsin esterolytic activity is primarily on the substrate (TAME) rather than trypsin itself. It was thought that TAME might be taken up into bile salt micelles and thus be more readily hydrolysed by trypsin, but we were unable to substantiate this hypothesis. The precision of the trypsin esterolytic assay was better when bile salts were not added. If however bile salts were to be used routinely in the trypsin assay, it would be useful to ensure that the concentration of calcium, included as activator, is sufficiently low to prevent the formation of a precipitate. This precipitate is probably a complex of calcium and bile salts.

Studies on the stability of pancreatic enzymes in duodenal fluid to storage temperature and pH.

The effects of storage pH and temperature on pancreatic amylase, lipase and trypsin in duodenal fluid were studied. All the enzymes were most stable when stored at --20 degrees C, while the optimum storage pH was found to depend on the particular enzyme under investigation.

An improved cation exchange HPLC method for the measurement of serum creatinine.

An improved HPLC method for the measurement of serum creatinine is described. Separation is effected using a strong cation exchange column at pH 4.7. Analytical recovery, precision and linearity are satisfactory, and the method correlates well with a kinetic Jaffé procedure. The method provides a means of accurately measuring creatinine and may be of use in the investigation of interference in creatinine assays.

External quality assessment of quantitative urinary analysis.

An external quality-assessment scheme was initiated among a group of 13 clinical chemistry laboratories for the urinary analysis of calcium, chloride, creatinine, glucose, osmolality, phosphate, potassium, protein, sodium, urate and urea and also for the estimation of creatinine clearance. The greatest inter-laboratory imprecision occurred in the assay of urinary protein. The results of the survey are compared with similar schemes elsewhere and their significance discussed.

Elimination of bilirubin interference in creatinine assays by routine techniques: comparisons with a high performance liquid chromatography method.

The aim of this study was to find a method for creatinine analysis unaffected by jaundice by comparing four different methods with high performance liquid chromatography (HPLC) as a reference method. The methods investigated were Kodak DTSC single slide, Boehringer alkaline picrate with and without blank correction and a Boehringer enzymatic method, the last three using the Hitachi 737 analyser. HPLC results were compared with the results of the methods studied. In addition, graphs plotting the difference from the HPLC result against the bilirubin concentration were made; the ideal method would yield a slope and intercept of zero. While all methods showed a positive bias compared with HPLC, the Kodak slide and the Boehringer alkaline picrate with blank correction methods eliminated bilirubin interference and we have changed to the latter method as a consequence of this work.

Serum creatinine assays in patients receiving the antibiotic Cefpirome (HR 810): a study of three different routine methods compared with a specific HPLC method.

Sequential timed samples were taken from patients after a single dose of a new cephalosporin--Cefpirome HR810. The patients had been recruited in a multi-centre trial over a 12-month period. Creatinine was estimated in all of these specimens by four different techniques, embodying four different analytical principles. Interference from the drug was evident in the assay depending on the Jaffe reaction. There was also interference in the enzyme-based methods, manifested as increased imprecision due to a non-specified cause thought to be related to the age of the samples. Only the HPLC method guaranteed precise results free from drug interference.

Modification of the Vickers SP120 continuous flow analyser to accommodate the Scandinavian recommended conditions of enzyme analysis for aspartate aminotransferase, lactate dehydrogenase and alkaline phosphatase.

It is important that recommendations of expert bodies for the estimation of enzymes are not undermined by laboratories at District General Hospital level adopting manufacturers' procedures. Three enzyme assay methods are presented which enable adaptation of SCE kinetic methods to the end point type of determination performed on the Vickers SP120 continuous flow analyser. Despite the differences in analytical principle, good precision and correlation was obtained.