A study of the thymol turbidity test with special reference to buffer behavior. Formulation of a modified reagent using tris-hydroxymethylaminomethane.

Replacement of barbiturate buffer by a tris-hydroxymethylaminomethane buffer in the thymol test reagent of Maclagan greatly improves the stability of the reagent. Thymol turbidity measurements made by means of the modified reagent agreed closely with those made with barbiturate-containing reagents. However in hyperlipemic sera, the latter reagent gave higher turbidities. A reaction of barbiturate with serum chylomicrons and triglycerides explains the difference. It is believed that the modified reagent is less likely to be affected by casual changes in serum lipid concentration and that therefore it should prove to be more dependable as an aid in the study of liver disease. Heating is not an essential operation in preparation of thymol test reagents. The pH is of critical importance in measurement of thymol turbidity. The large change in pH of barbiturate and Tris buffers with change in temperature makes careful control of temperature essential. Tables showing the appropriate reagent pH at various laboratory temperatures are presented.