Stability of mean assay values of magnesium and iron in lyophilized quality control serum: a study based on data from the quality assurance service (QAS) of the College of American Pathologists.

Data from magnesium and iron analyses of pools of lyophilized quality control serum were used to evaluate stability of analyte mean values in the pre-reconstitution period. Information was received from laboratories in Regional Quality Control Programs between 1977 and 1981, using CAP Quality Assurance Service data processing. For magnesium, 28 of 41 (68%) pool-method combinations were stable, 11 (27%) showed decreases, and 2 (5%) showed increases. Decreases averaged 0.008 mg/dL/month (all methods). A pronounced effect of method (automated methylthymol blue) and year correlated with decreases in measurable magnesium. For iron, 45 of 56 (80%) pool-method combinations were stable, 8 (15%) showed decreases, and 3 (5%) showed increases. Decreases averaged 0.349 g/dL (all methods). In most cases, changes in measured concentrations are attributed to methodologic factors, rather than intrinsic changes in analyte concentrations.

Source of analytic variation in ligand assay: a study based on data from the 1976 and 1981 Basic Ligand Assay Surveys of the College of American Pathologists.

Six paired specimens distributed to laboratories in 1981 at approximately three-month intervals and four paired specimens distributed to laboratories in 1976 at intervals of three to nine months for analysis by the College of American Pathologists Survey form the basis for this study. Twelve of 37 (35%) of pool-analyte-technic combinations yielded significantly changed mean values in 1976, while 34 of 196 (17%) pool-analyte-technic combinations yielded significantly changed values in 1981. Probable instability in thyroxine and folate was demonstrated in the 1981 control pools. Precision generally continued to improve from 1976 to 1981. The poorest precision now is observed in the analysis of peptide hormones. A majority of the observed analytic variation during 1981 for most analytes relates to extralaboratory factors. Improvement in performance is largely dependent on intermanufacturer standardization of procedures and long-term maintenance of equivalence of the results of kit procedures by each manufacturer.

Adaptation of microvolume EMIT assays for theophylline, phenobarbital, phenytoin, carbamazepine, primidone, ethosuximide, and gentamicin to a CentrifiChem chemistry analyzer.

We have developed microvolume EMIT procedures for theophylline, phenobarbital, phenytoin, carbamazepine, primidone, ethosuximide, and gentamicin using a centrifugal analyzer (CentrifiChem and Pipettor 1000) to reduce the manufacturer's recommended manual reagent consumption by one-sixth. In addition to developing the EMIT procedure, the performance of the analyzer and pipettor were verified. The analyzer and pipettor are capable of producing within-run precision at a 3-microliters sample volume and 210-microliters analyzer cuvette volume equal to or less than 1.5%. The performance of the EMIT procedures on the analyzer yielded spike drug recoveries of 90.8 to 106.1% for drug concentrations throughout the calibration concentration range of each assay. The percent error on standard reference material of the National Bureau of Standards ranged from a +12.0% to a -0.6% for ethosuximide, phenobarbital, phenytoin, and primidone. Patient comparison data yielded slopes from 0.930 to 1.110 for all assays. The other important feature of the adapted EMIT assay is its simplicity for use on a routine basis.

Precision in estrogen and progesterone receptor assays. Results of the first CAP pilot survey.

In this blind survey involving 47 unselected laboratories, 98% of participants concurred that a nominally mid-range estrogen receptor (ER) positive powder was positive; the concurrence was 91% for the progesterone receptor (PR). This precision exceeds the requirements imposed by the benefit: cost ratios which exist for the hormonal therapy of advanced breast cancer. In the same blind survey, the concurrence on nominally negative ER and PR specimens was 92% and 90%, respectively. These are also quite acceptable for the clinical context in which these tests are applied. Powders of human breast carcinoma are suitable for interlaboratory quality control. The particular lyophilized products we used were not as satisfactory.

Glucose stability in lyophilized chemistry quality control serum. A study of data from the quality assurance service (QAS) program of the College of American Pathologists.

Data from 2.5 million glucose analyses on pools of lyophilized human quality control serum were used to evaluate analyte stability in the prereconstitution phase. Input information was from laboratories in Regional Quality Control Programs that use CAP Quality Assurance Service (QAS) data processing. Of 31 pools in use between 1977 and 1981, decreasing glucose concentration was detected by, at least, one method in 26 pools, and by two or more methods in 21 pools. Method-associated average decrease in concentration varied from 0.13 mg/dL/month (glucose oxidase-electrode) to 0.19 mg/dL/month (automated glucose oxidase-colorimetric). Bidirectional instability as a function of analytic method, i.e., increase with "mild" methods, decrease with "rigorous" methods that was noticed previously with pools analyzed between 1973 and 1977, was no longer seen. Dominant directional changes in the later pools were downward by all methods, when statistically significant trends were demonstrated.

Analyte stability in clinical chemistry quality control materials.

Maximum stability of analytes in chemistry control materials is desired. Stability testing is customarily performed by manufacturers, both prior to distribution of products and during the period following distribution when the products are in the field. Users and evaluators of such materials periodically have reported on experienced stability of various analytes in distributed manufactured products. A wide variety of both testing protocols and definitions of acceptable stability have characterized published reports on the topic. In the present review, we summarize published studies on control material stability in clinical chemistry, review criteria employed to define instability, and present an approach to evaluating stability of analytes involving both statistical and clinical criteria.

Stability of sodium and potassium in lyophilized quality control serum. A study of data from the Quality Assurance Service Program of the College of American Pathologists.

The long-term prereconstitution stability of sodium and potassium in large pools of lyophilized quality control serum used in Regional Quality Control Programs, conducted between 1977 and 1980 is reviewed. In approximately one third of 27 pools studied, minimal but significant increases in sodium concentration were detected, these increases averaged less than 0.50 per year and confirmed our previously reported results from pools analyzed between 1973 and 1976. Results relating to potassium stability have been inconsistent. The previously reported tendency for potassium to increase in some pools was again suggested by data obtained from laboratories using automated flame-emission photometry procedures. This was not confirmed, however, by the data reflecting manual/semi-automated flame-emission photometry procedures or automated electrode methods. It is postulated, that the source of sodium causing the increases in concentration is the glass containers in which control materials are stored between the time of manufacture and reconstitution. Regression analysis against time of monthly interlaboratory means, from participants in Regional Quality Control Programs, is a useful tool for evaluating postmanufacture stability of analytes in pools used for daily internal quality control procedures.

Regional quality assurance for the 1980's, current status and future directions.

The current status of Regional Quality Control Programs has been summarized with respect to results of probes of data derived therefrom. Goals for the decade of the 1980's have been spelled out in the areas of program improvement and investigation of data. Primary areas for probing the data base are: analyte stability in quality control materials, state of the art in analytic precision and its relationship to analytical goals, accuracy assessment in regional programs, and utility of published criteria for establishment of antibiotic resistance or sensitivity by Kirby-Bauer technics.

Observation of a variant creatine kinase isoenzyme in sera and breast tumor cytosols.

A variant creatine kinase (CK) isoenzyme was identified in the sera of some patients who had advanced adenocarcinoma of the breast, stomach, and large intestine. A similar variant isoenzyme, together with a high concentration of CK-BB isoenzyme, was identified in some breast tumor cytosols. The variant creatine kinase activity in both sera and tumor cytosols was unaffected by antibodies specific for both the CK-M and DK-B subunits. This indicates that DK-MB isoenzyme determinations are currently best performed by electrophoretic rather than immunologic technics.

Estrogen receptor protein. Stability of 8S molecular form in frozen cytosols and practical criteria for its confirmation.

Estrogen receptor has been used in determining the efficacy of endocrine therapy in mammary tumors. Complete study of a tumor usually requires two procedures, a dextran-coated charcoal method for measuring binding capacity and binding affinity and a sucrose density procedure for confirmation of 8S protein, both of which are time consuming and expensive. A stability study of the 8S and 4S molecular forms in frozen cytosols at 24 hours, 48 hours, and one week was conducted. Some loss of these, forms after storage was evident, but in all cytosols studied, the two distinct forms could still be identified. Using a group of 100 tumor samples analyzed by both methods, practical criteria for determining when the 8S molecular form should be confirmed by a sucrose density gradient on the frozen cytosol have been formulated.

Stability of mean values of organic analytes in lyophilized quality control serum. A study utilizing data from the Quality Assurance Service (QAS) Program of the College of American Pathologists.

The long-term stability of mean values of six organic analytes in 48 commercial pools of lyophilized chemistry quality control serum is evaluated. These pools, provided by five manufacturers, have been used by nine Regional Quality Control Programs participating in the College of American Pathologists Quality Assurance Service. Creatinine yielded stable mean values in 88% of the pools studied. Both albumin and urea nitrogen demonstrated manufacturer and method-related changes in mean values. Bilirubin, cholesterol, and uric acid changes in mean values were independent of control serum manufacturer, predominant in calibrator-standardized automated procedures, and were clustered by years.

Changes in level of precision of common ligand assays during a seven-year interval.

Nine commonly performed radioligand analyses were studied for periods of four to seven years in terms of change in level of precision. Consistent improvement in precision is generally observed, except in specific instances when pool characteristics are altered to study sensitivity and crossreactivity.

Characterization of an inhibitor of hepatic cholesterogenesis present in hepatic microsomes.

An inhibitor of hepatic cholesterol synthesis present in hepatic microsomes can be solubilized either by an acetone or an ethanol powder preparation. Other methods such as methanol and chloroform:methanol powder preparations and treatment with EDTA do not solubilize the factor. The factor appears to be proteinaceous since its activity is lost after exposure to proteolytic enzymes and heat treatment. In addition, the inhibitor does not require a phospholipid for activity. 3this inhibitor is stable for long periods (60 hrs.) at room temperature and can be isolated in good yield from liver maintained at 4 degrees C for 8 hours postmortem.

Long-term stability of glucose in lyophilized quality control serum. A study utilizing data from the Quality Assurance Service (QAS) Program of the College of American Pathologists.

The long-term stability of glucose in 45 commercial pools of lyophilized quality control serum is evaluated. The pools have been used in conjunction with the Quality Assurance Service (QAS) of the College of American Pathologists by laboratories participating in Regional Quality Control Programs. Directional instability of glucose was detected by at least one analytic method in 69% of the pools studied. Two distinct and opposite directional trends in glucose concentration were found. Increasing concentration of analyte, averaging 4.7 mg/dl per year, were observed with manual and automated glucose oxidase methods and the automated neocuproine procedure in approximately one fourth of pool--method combinations. Decreasing concentrations of glucose, averaging 3.0 mg/dl per year, were found with automated ferricyanide and hexokinase methods and the manual orthotoluidine procedure in approximately one third of pool--method combinations. The results are best explained by postulating that in affected pools there is a gradual diminution of free and bound glucose and/or a shift of glucose from the protein-bound to the free state.

Reproducibility of mean values of duplicate specimens in the Basic Ligand Assay Survey.

Three paired samples were distributed at three--six-month intervals in the Basic Ligand Survey during 1976. The stabilities of mean values obtained by widely used commercial kit procedures and by all methods for eight analytes are reported. Significant improvements in accuracy and long-term precision were identified in assays for digoxin and thyroxine during 1976. However, a number of assays yielded unstable mean values that affected both within--laboratory maintenance of quality control and medical usefulness of the results.

Long-term stability of enzymes, total protein, and inorganic analytes in lyophilized quality control serum.

The stability of total protein and various enzyme and electrolyte analytes in numerous pools of lyophilized quality control sera is evaluated. Using data obtained between 1973 and 1976 from Regional Quality Control Programs utilizing the Quality Assurance Service of the College of American Pathologists, monthly group mean values are studied as a function of time, by means of linear regression analysis. In the 28 pools studied, unstable analyte-pool combinations were detected in approximately 35% of the cases. Total protein was the most universally stable. In a large percentage of pools, minimally increasing concentrations of sodium, chloride, and potassium were found, while inorganic phosphorus decreased in the majority of pools. In pools with changing enzymatic activiteis, alkaline phosphatase tended to increase and creatine phosphokinase generally decreased. Changes in levels of calcium, serum glutamic oxaloacetic transaminase, and lactate dehydrogenase were inconsistent. Changes in analyte concentration were judged in relation to the precision (SD) with which the analytes were measured. The ratios of rate of change in analyte value to SD were lower for electrolytes than for other analytes.

The role of regional quality control programs in the practice of laboratory medicine in the United States.

Since their initiation in 1967, Regional Quality Control Programs have expanded, and they are now accessible to all clinical laboratories in the United States. Based on input from large numbers of laboratories analyzing the same lots of control material for chemistry, hematology, and coagulation, the programs provide computer-generated intralaboratory statistics for day-to-day precision and interlaboratory comparative statistics for relative precision and accuracy. Nearly half the clinical laboratories in the United States currently participate in Regional Quality Control Programs in chemistry. These voluntary programs are coordinated by voluntary professional groups or by the manufacturers of control materials. Professionally directed programs are, for the most part, supervised by committees of state pathology societies.

Effect of renal microsomes and renal lysosomes on in vitro hepatic fatty acid synthesis.

An inhibitor and stimulator of in vitro hepatic fatty acid synthesis are present in renal microsomes. In addition, a stimulator of fatty acid synthesis is present in renal lysosomes. Renal microsomal inhibition of hepatic fatty acid synthesis is not due to the depletion of cofactors in the system. This inhibitor appears to be located exclusively in the kidney medullary microsomes. It is destroyed by Pronase and heat treatment suggesting it may be a protein. Its effects on fatty acid synthesis may be attributed in part to ATPase activity as well as a direct effect on the hepatic fatty acid synthesizing system. A stimulator of hepatic fatty acid synthesis is present in the buffer insoluble fraction of an acetone powder preparation of renal microsomes. This stimulator is relatively heat labile and does not appear to be a phospholipid. The lysosomal stimulator of hepatic fatty acid synthesis is associated with the contents of renal lysosomes and not with the lysosomal membranes. It acts at the acetyl-CoA carboxylase step and its activity is not affected by fasting or aminonucleoside induced nephrosis.