Low lipid level reference sera with human serum matrix

Time collection and storage conditions of lipid profile

The stability of samples is crucial for getting reliable concentrations of many analytes, including lipid profile. Thus, the goal of this study was to analyze lipid profile under different storage and temperature conditions. This was a prospective study with 809 patients of both genders. Total cholesterol, triglycerides, high-density lipoprotein cholesterol, low density lipoprotein cholesterol and non-high-density lipoprotein were measured within 1 h from collection at room temperature, after 2-3 h of refrigeration (8°C) and after 4-5 h at room temperature. The processing time and storage conditions did not affect the analytes measured. These findings are important for multicenter studies, because of the difficulties related to centrifugation and freezing of samples immediately after collection.

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.

Description of analytical problems arising from elevated serum solids

There has always been a problem with the collection of data and interpretation of the results obtained from any biological fluid in which the solids content was increased to a great extent. Of these solids, the triglycerides of the lipids may cause a plasma (serum) to vary in appearance from opalescent to milky. This condition of the specimen and the concomitant turbidity upon its addition to reagents creates the well-documented optical aberrations of spectrophotometric measurements. In addition, the lipids, in conjunction with the proteins, can act as diluents when they are elevated, thereby decreasing what might be termed the residual true plasma volume. Thus the water content of an aliquot sampled for a particular analytical procedure is diminished, and by that means a situation is created in which a short sample is drawn. This dilution effect by the solids results in a lowering of the assay values obtained for the measured constituents of such a serum sample. An associated phenomenon of high concentrations of solids, especially proteins, is the increase in viscosity of a specimen, a condition that also causes an error of short sampling when certain peristaltic pumping devices are used. This review considers several aspects of problems encountered when dealing with a number of circumstances that are critical to the measurement of analytes in severely hyperlipemic and/or hyperproteinemic specimens. These include the problems of short sampling; the potential amelioration of the problem by corrective mathematics, extraction of the lipids, or ultracentrifugation of the true plasma from the lipids; the important need to include most analytes into our considerations; the difference in reference base values for the calculation of concentrations of lipids of serum versus other analytes; the concept of the use of ratios when the reference base values differ, numerator analyte from denominator analyte; and the problems of using serum blanks when necessary corrective action for the solids volume is neglected. Thus, in the final analysis, problems with underestimated volumes of samples used for many spectrophotometric determinations are considered here along with the other difficulties encountered when the need to measure analytes in serums with extremely high solids content presents.

Interlaboratory comparison of serum thyroxine analyses

Approximately 300 clinical chemistry laboratories participated in a survey of measurements of the thyroxine (T4) concentration in 13 lyophilized serum specimens prepared by spiking a base serum pool with several different levels of T4. Of 35 commercially available kit methods, 4 kits were used by 30 or more laboratories, and 9 by 10 or more laboratories. Values obtained with the Abbott or Nuclear Medical laboratories, kits, which were used by one-third of all laboratories that named a specific kit, averaged 1 to 2 micrograms/dL greater than those obtained with the other methods. Within-run coefficients of variation were 10 to 20% for specimens containing less than 3 micrograms/dL of T4 and 3 to 6% for specimens with more elevated T4 levels.

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.