Prepation of hypercholesterolemic and-or hypertriglyceridemic sera for lipid determinations

Comparison between the triglycerides standardization of routine methods used in Japan and the chromotropic acid reference measurement procedure used by the CDC Lipid Standardization Programme

Background The US Centers for Disease Control and Prevention ensured adequate performance of the routine triglycerides methods used in Japan by a chromotropic acid reference measurement procedure used by the Centers for Disease Control and Prevention lipid standardization programme as a reference point. We examined standardized data to clarify the performance of routine triglycerides methods. Methods The two routine triglycerides methods were the fluorometric method of Kessler and Lederer and the enzymatic method. The methods were standardized using 495 Centers for Disease Control and Prevention reference pools with 98 different concentrations ranging between 0.37 and 5.15 mmol/L in 141 survey runs. The triglycerides criteria for laboratories which perform triglycerides analyses are used: accuracy, as bias ≤5% from the Centers for Disease Control and Prevention reference value and precision, as measured by CV, ≤5%. Results The correlation of the bias of both methods to the Centers for Disease Control and Prevention reference method was: y (%bias) = 0.516 × (Centers for Disease Control and Prevention reference value) -1.292 ( n = 495, R²= 0.018). Triglycerides bias at medical decision points of 1.13, 1.69 and 2.26 mmol/L was -0.71%, -0.42% and -0.13%, respectively. For the combined precision, the equation y (CV) = -0.398 × (triglycerides value) + 1.797 ( n = 495, R²= 0.081) was used. Precision was 1.35%, 1.12% and 0.90%, respectively. It was shown that triglycerides measurements at Osaka were stable for 36 years. Conclusions The epidemiologic laboratory in Japan met acceptable accuracy goals for 88.7% of all samples, and met acceptable precision goals for 97.8% of all samples measured through the Centers for Disease Control and Prevention lipid standardization programme and demonstrated stable results for an extended period of time.

A simple procedure for the preparation of concentrated sera

We shall describe a simple technique to prepare concentrated sera that will have a near normal osmolality. A pool of sera is first frozen for 72 h at -20 degrees C and then allowed to thaw at 6 degrees C for 16 h. Care is taken to avoid any shaking of the bottle. The surface serum is then cautiously aspirated with a pipette. The left-over serum is mixed and filtered. To decrease the osmolality of this concentrated serum, we treated it with 200 mg of resin (Rexyn AG 501, H-OH) per 5 mL serum and then filtered it to eliminate the resin. We studied the effects of the height of the liquid column, the freezing temperature, the volume of serum decanted, the resin concentration and the duration of the extraction step. We also evaluated the stability of this concentrated serum at 6 degrees C, -20 degrees C and -70 degrees C. We also verified whether readjustment of the pH of the concentrated resin-treated serum would have improved its stability at -20 degrees C.

Evaluation of four reagents for delipidation of serum

Four reagents, Aerosil 380, Freon 113, Dextran sulfate 500-S, and a mixed organic solvent were tested for their abilities to produce optically clear, pooled human serum. Aerosil-380, a silicon dioxide, removed 95% of serum cholesterol and triglycerides, and 80% of the free fatty acids. A mixed organic solvent (n-butanol:diisopropyl ether) was equally effective, but also removed nearly all endogenous alkaline phosphatase and lactate dehydrogenase. Freon-113 and Dextran sulfate 500-S removed about half of the serum cholesterol and triglycerides. The serum content of several non-lipid components was unaffected by Aerosil-380, Freon-113, and Dextran sulfate treatments; however, the mixed organic solvent removed 69% of the endogenous calcium. Light scattering data revealed that treatment with all reagents except the mixed organic solvent resulted in optically-clear serum products.

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.

Preparation of reference sera with desired levels of cholesterol and triglyceride

Simple methods for isolating cholesterol-rich protein fraction from human serum and triglyceride-rich fraction from hen egg yolk are presented. The isolated fractions are combined separately with small volumes of human serum in order to stabilize concentrated cholesterol and triglyceride. Precalculated volumes of concentrates are added to human serum in order to prepare reference sera with desired levels of cholesterol or triglyceride, or both. The reference sera resemble human serum in appearance, composition, and stability. Properties of preparations are discussed and stability of reference sera is illustrated.

Problems associated with clinical chemistry quality control materials

Quality control methods and materials are widely used to monitor each and every facet of clinical chemistry laboratory performance. Quality control materials are also used in evaluation of methods and as secondary standards. A wide range of liquid and lyophilized materials are available from commercial sources and are prepared in individual laboratories. Many problems arise in the use of quality control materials. Problems discussed in this review include the use of nonhuman based materials and additives of animal origin, the physical and chemical characteristics of quality control materials that differentiate such samples from those from patients, attempts to generate quality control materials with elevated levels of particular analytes, the difficulties in handling and storage of quality control materials, the dangers of hepatitis, and the stability of quality control materials both during storage in the laboratory and after their reconstitution. The advantages and disadvantages of liquid and lyophilized quality control materials are discussed. The assignation of analyte values is of particular importance as the current trend is to consider inaccuracy of laboratory methods in addition to imprecision. This review assesses relevant publications in an area of fundamental importance to quality control in clinical chemistry.

Automated determination of total plasma cholesterol: a serum calibration technique

The automated (AutoAnalyzer II) determination of cholesterol in nine serum pools in the concentration range 3.465-8.871 mmol/l, gave results that were approximately 10% higher than reference values when the analyses were based on unesterified cholesterol standards containing the same amount of water as the sample extracts (1963 analyses in 12 laboratories during a 12 month period; automated value = 0.032 + 1.10 X (Reference value)). A serum calibration procedure was successful ilues, and was equally effective in correcting the values observed for aliquots of 368 fresh-frozen plasma samples analyzed in each of the 12 laboratories during a 38 month period.

Regression analysis in interlaboratory surveys: a case study with cholesterol and triglycerides

1. A new interlaboratory survey design, that uses regression analysis to compare results from each laboratory with target values, was tested using cholesterol and triglyceride analyses. The fifty New Zealand laboratories involved showed considerable interlaboratory variation (CV = 8% to 27% for cholesterol, 13% to 113% for triglycerides), 30% and 40% of which was associated with systematic differences between laboratories. 2. End-of-period summaries using regression analysis confirmed the presence of systematic errors. These were either simple types caused apparently by incorrect standardisation (regression slope, B not equal to 1.0) or inappropriate blank correction (intercept, A not equal to zero) or complex types presumably due to nonlinearity or nonspecificity. Graphical display of results from each laboratory aided fault diagnosis and allowed the detection of between-run standardisation differences. 3. Method comparison studies were made: the only highly significant result being lower precision achieved by enzymatic cholesterol methods compared with other colorimetric methods.

Serum lipids and latent coronary insufficiency

A group of 2014 'healthy' men were examined clinically, by resting ECG/exercise ECG and by the estimation of serum cholesterol and triglycerides. On repeated collection of specimen, standardization of factors related to the individual and influencing serum lipids was difficult to obtain. Thus, serum triglycerides were higher early in the week, at least partly due to habits of alcohol consumption. 140 of the participants (7.0%) were suspect of coronary heart disease (CHD) according to their symptoms/signs, and coronary angiography in 105 of them showed sixty-nine cases (3.4%) with pathological angiograms. Values for serum cholesterol and triglycerides are presented from a subgroup of 1832 men where no signs of CHD were found. Serum cholesterol and triglycerides were significantly higher in the group with pathological angiograms.

Factors involved in the determination of triglycerides in serum: an international study

Ten laboratories analysed five different specimens in duplicate on ten separate occasions by one, or several, of five common triglyceride methods. Simple statistical data are presented and, as far as possible, these are interpreted in the light of the methods used and the results of chemical analyses of the materials. Great variability was found between the results of the participating laboratories. The major factor involved seems to be the material specific nature of the methods under study. At least one method in common use is contraindicated.