Reference sera with graded levels of high density lipoprotein cholesterol.

A two-step procedure for the separation of low density lipoprotein (LDL)-rich fractions and high density lipoprotein (HDL)-rich fractions from human serum is presented. The isolated precipitates are combined separately with small volumes of human serum in order to stabilize the lipoproteins. Calculated volumes of concentrates are added to human serum or to delipidated human serum [1], so that reference sera with graded levels of high density lipoprotein cholesterol (HDLC) can be prepared. These reference sera resemble human serum in appearance, composition and fractionation by ultracentrifugation. Our evaluations of the materials described in this communication have shown them to be suitable for HDLC determinations, using the precipitation procedure with heparin-manganese chloride. Properties of these reference materials are discussed.

Suitability of frozen and lyophilized reference sera for cholesterol and triglyceride determinations.

Observations on the suitability of frozen and lyophilized reference sera stored at -20 degrees C are presented. These sera, intended for use as controls for both cholesterol and triglyceride determinations, covered ranges for cholesterols from 4 to 8 mmol/l and for triglyceride from 0.7 to 2.4 mmol/L. We observed no change in cholesterol or triglyceride concentration in either the frozen or lyophilized forms of serum during almost 5 years of storage. The suitability of these materials for cholesterol and triglyceride determinations is demonstrated by representative methods. Our results show that lyophilized reference sera can be shipped unprotected by dry ice without any effect on cholesterol or triglyceride concentration. Although the total cholesterol concentration was unchanged with storage, changes did occur in the lipoproteins carrying these lipid constituents.

Low lipid level reference sera with human serum matrix.

We describe a simple procedure for preparing low lipid level reference sera containing concentrations of nonlipid components similar to the concentrations in human serum. A portion of human serum is delipidized with colloidal silicic acid, and the delipidated serum, in selected proportions, is combined with the native serum. These reference materials can be used as internal or external quality controls in conjunction with low total cholesterol and low high-density lipoprotein (HDL) cholesterol determinations in serum or plasma. They can also be used as controls with low triglyceride determinations.

Automated development of a kinetic method for the continuous-flow determination of creatinine.

A "stopped-flow" method for the kinetic Jaffé determination of creatinine was developed, with the use of a computer-controlled continuous-flow system. Simplex optimization was used to find conditions of hydroxide and picrate giving maximum sensitivity for creatinine. We used a modified central composite experimental design to evaluate creatinine sensitivity and albumin, glucose, and acetone interferences as functions of hydroxide and picrate concentrations. More importantly, this work illustrates that the automated development of clinical chemical methods offers an efficient means of obtaining optimized, well-understood analytical procedures for subsequent routine use in the clinical chemistry laboratory.