We evaluated six precipitation methods for high-density lipoprotein cholesterol (HDL-chol) determination: the heparin/Mn2+precipitation reagent method (Hep), two variants of the phosphotungstic acid/Mg2+ method (Tung-L and Tung-B), the dextran sulfate 50 000/Mg2+ method (Dex), the PEG 6000 method (PEG), and the PEG 6000/dextran sulfate 15 000 (PEG/Dex) method. The Tung-B and PEG/Dex precipitation methods have a low sample/precipitation reagent volume ratio (<0.4). The Tung-B, Dex, PEG, and PEG/Dex methods gave similar values, averaging within 0.1 mmol/L of each other, showing that the precipitation selectivity of these methods is comparable. The precipitation efficiency of Tung-B and Peg/Dex, however, was superior. Ultrafiltration of the supernatants was needed only at triglyceride concentrations >16.4 mmol/L (undiluted sample) or >28.0 mmol/L (sample diluted twofold); however, ultrafiltration without dilution was the most accurate method. Results of Tung-B under routine conditions (33 technicians) agreed well with those of the PEG method for 406 normo- and hyperlipidemic plasma samples. By comparison with the HDL-chol method from the Centers for Disease Control and Prevention, the Tung-B method showed a total error of 10.6%, which fulfills the criteria of the National Cholesterol Education Program for HDL-chol analysis. In conclusion, with motivated personnel, Tung-B is a reliable, cost-effective method for routine HDL-chol analysis.

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We studied the suitability of various types of human serum preparations to test the accuracy of total cholesterol measurements in the External Quality Assessment scheme in The Netherlands, in which approximately 180 laboratories participate. Checked against the certified Abell/Kendall Reference Method, large reagent-dependent negative biases were observed with lyophilized serum that was insufficiently cryoprotected. The biases for the reagents of Du Pont, Roche, and Beckman averaged -16.7%, -9.2%, and -7.6% respectively; the least bias, -0.4%, was obtained with reagent from Boehringer Mannheim. The beneficial effect of cryoprotection with sucrose was demonstrated by the decrease in interreagent variation from 5.4% to 1.9%, the latter value being comparable with the values for fresh and once-frozen pooled serum (1.3% and 1.7%, respectively). We conclude that the detrimental effect of lyophilization on serum matrix can be minimized by suitable cryoprotection with 200 g/L sucrose.

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The three most important enzymes present in duodenal fluid, α-amylase, trypsin and lipase, were determined by two different methods. Various dilution fluids for these determinations were compared. Some kinetic data are described together with the reproducibility of the assays. For α-amylase the Phadebas method was compared with an UV method. Trypsin was determined using an immunoreactive trypsin test and a titrimetric method, while lipase was determined with a titrimetric method and a Cu-soap method.There was very good agreement between the two α-amylase methods and between the two trypsin determinations. There was also good agreement between both lipase methods.The advantages and disadvantages of all the methods are discussed. Bestimmung von a-Amylase, Trypsin und Lipase in Duodenalsaft: Ein Vergleich von MethodenZusammenfassung: Die drei wichtigsten Enzyme im Duodenalsaft, α-Amylase, Trypsin und Lipase, wurden mit zwei verschiedenen Methoden bestimmt. Es wird ein Vergleich zwischen verschiedenen Fl ssigkeiten zur Verd nnung gezogen. Einige kinetische Angaben werden zusammen mit der Reproduzierbarkeit beschrieben. F r α-Amylase wird ein Vergleich zwischen der Phadebas Methode und einer UV-Methode gezogen. Trypsin wurde mit dem Test auf immunoreaktives Trypsin und einer Titrationsmethode bestimmt, w hrend Lipase mit einer Titrationsmethode und einer Cu-Seifen-Methode bestimmt wurde. Der Vergleich von beiden α-Amylase-Methoden war gut, ebenfalls zwischen beiden Trypsin-und beiden Lipase-Methoden.Die Vorteile und Nachteile aller Methoden werden besprochen.