Drugs in blood donors.

CLINICAL CHEMISTRY, Vol. 33, No. 1, 1987 189 tubes containing 200 ML of 0.6 mol/L HC1O4; thus deproteinization was instantaneous. The tubes were centrifuged within 1 h and the clear protein-free supernate was stored at 4 #{176}C until assayed. Such deproteinized samples were stable for at least two months at 4 #{176}C and were analyzed without prior neutralization. Lactate was measured with an enzymatic kit reagent (cat. no. 149993; Boehringer, Mannheim, F.R.G.) adapted to a Cobas Bio centrifugal analyzer (Roche, Basel, Switzerland). The reagent solution, prepared by adding 5 mL of the carbonate buffer solution plus 100 /.LL of the enzyme suspension to one vial of NAD , was used within 1 h after preparation. The analyzer was programmed to dispense 25 ML of sample, 20 ML of diluent, and 300 ML of reagent. The change in absorbance at 340 nm was measured between 3 s and 10 mm after mixing (instrument setting: “type of analysis 4”). Reagent drift increased with increasing reaction temperature and pH of the sample. The assay temperature was therefore set at 25 #{176}C and the reagent blank was determined with a sample of 0.54 mollL HC1O4. Lactate standards were prepared in 0.54 moIJL HCIO4. Separate sample-blanks were not necessary. The extended linear range for the method (from 0.65 mmol/L up to 25 mmolJL in the original sample) allowed quantification, without further dilution, of all samples obtained during graded exercise tests. The method is reliable, day-to-day CVs being <5% and 8%, respectively, for concentrations exceeding and <1 mmol/L. Analytical recovery of lactate added (1-20 m.moIIL) to blood samples averaged 104%. This method is suitable for assaying lactate in small volumes of arterialized blood, as required for accurately determining the anaerobic threshold during exercise tests; it can easily be adapted to other analyzers in which prompt initial readings can be made.