We describe a simple, direct, and specific manual method for quantitative determination of total cholesterol in serum. In the method, which requires no extraction of the serum, a single stable reagent and 50 µl of sample is used. Serum cholesterol concentrations determined by this method did not differ statistically from those obtained by the reference method of Abell et al. Hemoglobin, bilirubin, and γ-globulin do not interfere unless present at markedly supranormal concentrations. Inter-run precision is about ±3% (95% confidence limits).

A simple method is described for directly determining serum urea nitrogen, wtihout deproteinization. The urea in 20 µl of serum or plasma is reacted with diacetylmonoxime in the presence of thiosemicarbazide and cadmium ion under acid conditions. The absorbance of the resulting rose-purple solution is measured at 540 nm. Results agreed excellently with those obtained by a reference method that makes use of urease and the Berthelot phenate—hypochlorite reaction for ammonia. An automated adaptation utilizing the AutoAnalyzer is also described, which eliminates the need for a dialyzer. A further advantage is that the same reagents are used for both methods.

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