Clinical Chemistry Analytes Research Articles

Inter-Laboratory Evaluation of the COBAS INTEGRA® 400 Analytical System

COBAS INTEGRA 400 is a random-access analytical system consolidating assays for clinical chemistry analytes, electrolytes, serum proteins, drugs of abuse and therapeutic drugs. Analytical performance and practicability of the instrument were evaluated in seven laboratories over a 2-year period in parallel with system development. Good within-run and total imprecision for all assays was observed with a few exceptions for specimen pools with low concentration or activity. The coefficients of variation for total imprecision were well below 3.0% for clinical chemistry analytes and electrolytes, and below 5.0% for serum proteins and therapeutic drugs. Method comparisons demonstrated a good agreement with the various systems used for comparison, with slopes varying typically from 0.94 to 1.05, and Spearman correlation coefficient generally > 0.975. Accuracy was verified by recovery of controls and certified reference materials within 90 to 110% of target values. Assay ranges were linear within +/- 5%. No carry-over on reagent or sample pipetting systems was observed. Manufacturer-specified interference limits and onboard stabilities of reagents were confirmed. A time study for calculating direct personnel times and total processing time was carried out in three laboratories under different conditions including consolidated, STAT and dedicated use. On a scenario-independent basis, the total working time was shorter on the COBAS INTEGRA 400 than on routine systems in all three laboratories. Personnel time, in particular, was significantly reduced when compared to routine instruments. In general, system practicability was judged very positively in all laboratories. Owing to its versatility, the instrument is best placed as a consolidated workstation in small- to medium-sized laboratories or as an instrument for special determinations such as serum proteins, drugs, urinalysis or emergency analyses in large laboratories.

Standardization of laboratory data and establishment of reference intervals in the Fukuoka Prefecture: a Japanese perspective.

Standardization of 22 clinical chemistry analytes and five serum protein constituents has been performed in the Fukuoka Prefecture, which has a population of approximately five million. The standardization project was established to determine reference intervals for these analytes by educating physicians, medical technologists and staff of medical institutions, and by daily or monthly monitoring the use of common control samples through e-mail. Standardization extended to 97% of the institutions in the prefecture. Results for 14 of the 22 clinical chemistry analytes have become highly reliable and differences between institutions decreased. Standardization of other analytes is now in progress. Regional collaboration based on international guidelines led to a significant improvement in interlaboratory comparability. Areas where further improvements are needed have been identified.

Stability of Clinical Chemistry Analytes in Blood Collection Devices

During the AACC Annual Meeting in New Orleans in July 1999, Greiner Meditech Inc. (Bel Air, MD), distributed sample packages with labeling claiming that their serum and plasma Vacuette® blood collection tubes with clot activator and separation gel for clinical chemistry analyses are capable of maintaining the stability of all analytes during storage for 48 h without affecting the serum or plasma values (1). I found similar 48-h stability claims for the Vacuette blood collection devices on Greiner’s Web sites in the United States and Europe (2)(3). In addition, colleagues in laboratories in Spain had received Greiner Vacuette product information with universal 48-h stability claims (4). Data supporting the claims described above were not provided in any of the above instances and could not be found during an extensive literature …

Clinical laboratory diagnosis and aging. 2: Suitability of clinico-chemical basic parameters as markers ob biological aging

In 262 men (about half of them 44.4 +/- 0.9 and 63.0 +/- 0.9 years old, resp.) and 239 women (about half of them 44.4 +/- 0.9 and 62.8 +/- 0.8 years old, resp.) the results of 12 clinical chemical analytes were used to calculate laboratory indices which were compared with the biological age in accordance with Ries. The indices were calculated by using concentrations of alkaline phosphatase, iron, total protein, total cholesterol, glucose, uric acid, urea, HDL cholesterol, creatinine, LDL cholesterol, transferrin, and triglycerides. Only in the younger group of women are the correlations between laboratory indices and biological age significant. In the same group, several single parameters also significantly correlate with pre-aging. Among them are alkaline phosphatase, the LDL-C/HDL-C ratio, bilirubin, triglycerides, and glucose.

Clinical laboratory diagnosis and aging. 1: Results of data evaluation of clinico-chemical laboratory values in a study of aging

The results of the determination of 24 basic blood chemistry variables from 262 men and 239 women, half of each group 44.4 +/- 0.9 and 63.0 +/- 0.9 (men) and 44.4 +/- 0.9 and 62.8 +/- 0.8 years old (women), resp., are compared. In men, only 6 analytes show significant differences between the age groups: Alanine aminotransferase decreases, aspartate aminotransferase decreases, iron decreases with p < 0.05; sodium increases, calcium decreases, protein (serum) decreases with p < 0.001. In women, 16 analytes, compared between both groups, are significantly different: Urea, uric acid, creatinine, triglycerides, total cholesterol, LDL cholesterol, LDL-C/HDL-C ratio, alanine aminotransferase, alkaline phosphatase, gamma-glutamyltransferase, sodium and ferritin are increased in the older group, whereas HDL cholesterol, iron, transferrin, and total protein are decreased. The sex differences are more distinct in the group of 44 years old persons than in the 63 years old one. These results will be completed by the comparison with the evaluation of the stored laboratory values of 9923 patients between 20 and 89 years old.

Reference Intervals for 18 Clinical Chemistry Analytes in Fetal Plasma Samples Between 18 and 40 Weeks of Pregnancy

The intrauterine biochemical assessment of the human fetus is important in fetal medicine, for both prenatal diagnosis and therapy of fetal diseases. Percutaneous umbilical blood sampling (PUBS) performed with ultrasound guidance is reliable for this, and the microvolume specimens obtained by this technique are readily analyzed by modern clinical chemistry analyzers to perform complete biochemical profiles with small blood volumes. The interpretation of fetal biochemical tests requires age-gestational specific reference intervals to reveal possible pathological processes and to minimize the remarkable physiological variability observed with fetal growth and maturation, particularly in the last trimester of gestation. Various cord blood analytes have been investigated as potential indicators of fetal distress (1)(2), but no comprehensive report of reference intervals adjusted to various weeks of gestation has been available. Here, we present reference intervals for 18 analytes in plasma samples obtained by PUBS from 72 healthy fetuses between weeks 18 and 40 of pregnancy. We analyzed plasma from 171 fetuses who underwent PUBS between the 18th and 40th week of gestation for various indications (Rh alloimmunization 79, maternal viral or parasitic infection 42, rapid karyotyping 25, and maternal thrombocytopenia 25). Informed consent was obtained from the parents. Gestational age at the time of sampling was determined from menstrual dates or by ultrasonography when the dates were uncertain. We selected 72 fetuses as “healthy” when the …

In vitro interference of the red cell substitute pyridoxalated hemoglobin-polyoxyethylene with blood compatibility, coagulation, and clinical chemistry testing

Objectives: Pyridoxalated hemoglobin-polyoxyethylene (PHP) is a prototypical red cell substitute approved for phase I studies. Peripheral blood smears of human blood mixed with PHP in 1 to 4 g/dL concentrations showed dose-dependent red cell aggregation and rouleaux. Whether this aggregation limits interpretation of blood compatibility testing and whether the intense coloration of serum or plasma containing PHP affects routine coagulation and clinical chemistry measurements was tested. Design: In vitro studies. Setting: University hospital laboratory. Participants: Four healthy volunteers, blood types A, B, AB, and O. All were Rh+. Measurements and Main Results: ABO typing, Rh typing, and antibody screening and coagulation studies were performed on blood: PHP admixtures having final concentrations of 1, 2, and 4 g/dL. For clinical chemistry interference studies, known concentrations of analytes were added to a serum matrix containing PHP ABO (forward) and Rh typing showed no interference in the three concentrations tested. Reverse ABO typing and antibody screening showed rouleaux at 4 g/dL, which corrected with routine saline replacement. Partial thromboplastin time (PTT), prothrombin time (PT), and fibrinogen showed no clinically significant differences from the controls. Results for electrolytes, renal function analytes, and markers of cardiac injury were acceptable by standard laboratory methods. However, results of liver function tests were unacceptable in PHPcontaining specimens. Conclusions: PHP-induced aggregation was observed with high PHP concentration; however, compatibility testing was not affected because agglutination was corrected by saline replacement, which is standard practice. Although routine blood banking, coagulation, and most clinical chemistry analytes can be measured reliably, alternative methods and strategies are needed for assessing liver function in the presence of PHP.

Variability in the measurement of C-reactive protein in healthy subjects: implications for reference intervals and epidemiological applications

We developed a reproducible ELISA for C-reactive protein (CRP), calibrated with WHO Reference Material, for which intra- and interassay CVs were 3.0% and 6.0%, respectively. Analytical recovery was 97.9%. The distribution of CRP in a healthy blood donor population (n = 143) was nongaussian, with 2.5th, 50th, and 97.5th percentile values of 0.08, 0.64, and 3.11 mg/L, respectively. There was no sex-related difference, and the association with age was weak. In a study of variability [by the method of Fraser and Harris (Crit Rev Clin Lab Sci 1989;27:409-37)], the analytical variability was 5.2%; the within-subject variability, CVI, was 42.2%; and the between-subject variability, CVG, was 92.5%. The critical difference for sequential values significant at P < or =0.05 (i.e., the smallest percentage change unlikely to be due to analytical variability or CVI) was calculated as 118%, and the index of individuality, CVI/CVG, was 0.46. This suggests that CRP, like many clinical chemistry analytes, has limited usefulness in detecting early disease-associated changes when used in conjunction with a healthy reference interval. From a molecular epidemiological standpoint, the usefulness of CRP in longitudinal studies is suggested by the small index of individuality and by observations that (a) short-term fluctuations were infrequent, (b) all data stayed within the reference interval, and (c) relative rankings of the subjects over 6 months only moderately deteriorated.

Reference intervals for 21 clinical chemistry analytes in arterial and venous umbilical cord blood

Reference intervals were determined for 21 clinical chemistry analytes in umbilical cord arterial and venous blood from healthy term infants. Nonparametric analysis (rank number) was used to determine the central 95% reference interval. No significant differences were observed between male and female infants. Reference intervals for glucose, urea, creatinine, urate, phosphate, calcium, albumin, total protein, cholesterol, triglycerides, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, creatine kinase, lactate dehydrogenase, gamma-glutamyltransferase, and magnesium all were significantly different from adult values.

Comparison of Plastic vs. Glass Evacuated Serum-Separator (SSTTM) Blood-Drawing Tubes for Common Clinical Chemistry Determinations

We evaluated a plastic evacuated blood-drawing tube containing an integral serum-separating barrier gel, by direct comparison with a glass counterpart. The plastic tube demonstrated no differences when compared for common clinical chemistry analytes with multiple types of instruments and systems. A total of 260 such different combinations were studied with emphasis on tests sensitive to drawing and handling indexes such as lactate dehydrogenase and potassium. A total of six separate blood drawings were tested with no significant differences noted in these tests. The total study included subjective evaluations of the plastic tube's use as a blood-drawing device and objective studies based on quantitative test results from normal and hospitalized patients and use of the primary sampling tubes (both plastic and glass) for 48-h storage.

Clinical chemistry reference intervals for healthy elderly subjects

In 1979, 304 healthy elderly individuals in New Mexico were recruited for a longitudinal study of nutrition and aging. Repeat measurements on a yearly basis of commonly requested clinical chemistry analytes allowed the calculation of reference intervals, between and within-subject variance components, and percentiles for change in concentration between two yearly measurements. The latter was further divided into analytical and biological variance components. The upper 95th percentile for the difference between two yearly measurements, expressed as a percent of the population mean, ranged from 4% for Na+ to approximately 20% for total cholesterol and to greater than 90% for ferritin. Year-to-year differences attributable to the biological component ranged from a low of 2% of the population mean for Na+ to 70% for gamma-glutamyltransferase.

Clinical chemistry reference intervals for healthy elderly subjects

In 1979, 304 healthy elderly individuals in New Mexico were recruited for a longitudinal study of nutrition and aging. Repeat measurements on a yearly basis of commonly requested clinical chemistry analytes allowed the calculation of reference intervals, between and within-subject variance components, and percentiles for change in concentration between two yearly measurements. The latter was further divided into analytical and biological variance components. The upper 95th percentile for the difference between two yearly measurements, expressed as a percent of the population mean, ranged from 4% for Na+ to approximately 20% for total cholesterol and to greater than 90% for ferritin. Year-to-year differences attributable to the biological component ranged from a low of 2% of the population mean for Na+ to 70% for gamma-glutamyltransferase.

Biological variability of 26 clinical chemistry analytes in elderly people.

Analytical, within-subject, and between-subject components of variation were estimated for 26 clinical chemistry analytes from duplicate analyses of 10 specimens collected from 27 healthy elderly subjects over a period of 20 weeks. Within-subject variations were similar to those generated previously by us in younger subjects. We conclude, therefore, that homeostasis is not compromised by age alone, and biological variability does not increase simply with age. All analytes except serum water had marked individuality, showing that conventional population-based reference values are of limited utility. The critical differences required for two results to be significantly (P less than or equal to 0.05) changed are not the same as those that prompt action by clinicians. Although heterogeneity of within-subject variation does exist, we believe that the critical differences generated will be useful in routine clinical decision making.

Proficiency testing in a medical-needs context.

Proficiency testing by State and Federal agencies is an ongoing activity of clinical laboratories and an occasional source of anxiety; strict statistical evaluations of "snapshot" laboratory values are inappropriate and medical-needs criteria should be used. The quality of laboratory results largely depends on available technology. Fortunately, for most of the common clinical chemistry analytes there has been a steady reduction of imprecision during the past 20 years. Proficiency testing may have been the stimulus for this improved performance. Medical-needs criteria differ, depending on the testing goal. For proficiency testing, population screening criteria are appropriate, e.g., the College of American Pathologists fixed criteria for the common tests. Stricter criteria are needed for short-term (inpatient) and long-term (outpatient) monitoring of laboratory data. Explicit proficiency-testing limits are given here for nine of the common clinical chemistry tests for each of the three medical-needs criteria described above. The limits consider total error--i.e., bias from the believed correct value, and imprecision. Rather broad limits are acceptable for the commonly performed enzyme tests when used for screening purposes.

A self-consistent set of reference values for 23 clinical chemical analytes.

Heparinized plasma of 528 blood donors was subjected to the 23 most frequently ordered chemical and enzymatic tests. The central fraction of the distribution of all results for each test was estimated. Out of the 528 donors a reference population has been selected. Because of the lack of other criteria, the result for any test of a blood donor was selected as a value belonging to the reference population if the results for the other 22 analytes of this particular donor lay within their own central fraction. On this basis an iterative procedure for the selection was programmed, considering the interaction between tests. The procedure was stopped when the reference limits for all 23 tests were converging. Fractions from 0.90 to 0.98 were applied to results for men and women donors separately. The elimination procedure and the criteria to select the best fitted fraction are discussed. The derived reference intervals are designated a "self-consistent set of reference values."

Generation and application of data on biological variation in clinical chemistry.

Most clinical chemical analytes vary in a random manner around a homeostatic set point. Replicate analyses of a series of specimens collected from a group of subjects allows estimation of analytical, within and between subject components of variation. The preferred experimental procedures and statistical methods for evaluation of data and analysis of variance are described; a detailed example is provided in the Appendix. The many uses of data on biological variation in clinical chemistry are reviewed, including setting analytical goals, deciding the significance of changes in serial results from an individual, evaluating the utility of conventional population-based reference values in patient management, and other applications.

Selected Analytes in Clinical Chemistry.

Selected Analytes in Clinical Chemistry.

The application of two-dimensional centrifugation to clinical chemistry testing.

We have developed a new clinical chemistry analyzer, the VISION System, which uses centrifugal force to separate whole blood, measure reagent and plasma volumes, and complete all steps required for a spectrophotometric analysis. The system is based on a multichambered test pack containing liquid reagents, which can be centrifuged in two planes oriented at right angles to each other. The analyzer regulates the temperature, timing and optical measurements for up to 10 different test packs in the same run. We have demonstrated good precision and accuracy on 6 clinical chemistry analytes, 2 enzymes, potassium and theophylline using this system.

Application of reflectance spectroscopy to the estimation of uric acid, urea and glucose: an evaluation of the Ames Seralyzer

An original approach to the measurement of analytes in clinical chemistry has now become available, in which dry reagent strip technology is linked to measurement by reflectance spectroscopy. The present studies have evaluated the performance of the first of these test systems-for uric acid, urea and glucose, in serum-by comparison with conventional liquid chemistry methods. Satisfactory performance in terms of both precision and accuracy was obtained for all three test systems, the current "state-of-the-art" performance criteria being met; the Seralyzer system proved reliable and easy to use in the hands of trained operators. It should find a place as a "Stat" analyser in the laboratory, in specified wards and in Health Centres.

The multivariate reference range: an alternative interpretation of multi-test profiles.

To test the utility of multivariate interpretation of laboratory data, we developed a multivariate reference range based of the Mahalonobis distance (D2) measure. Results for 20 commonly measured clinical chemistry analytes were collated for two sophomore medical-school classes (118 and 143 individuals in 1979 and 1980, respectively). The data for each test were examined for fit to a gaussian (normal) distribution by using a Kolmogorov--Smirnov test. Those results discovered to have a non-normal distribution were "normalized" by used the of a two-stage log-exponential transform. After this transformation, the D2 distance for each student group followed the expected chi-square distribution with 20 degrees of freedom. For each student's D2 distance an associated chi-square percentile was derived, and a cutoff percentile (95%) was selected to differentiate multivariately the "normal" from "abnormal" test results. Whereas more than two-thirds of the students had univariate test abnormalities, fewer than 7% had abnormal multivariate D2 scores. Analysis showed that the multivariate reference range could sensitively detect minor variations of multiple analytes but could also be quite insensitive to highly abnormal results for a single analtye. The multivariate approach has promise as a tool to avoid unnecessary followup of falsely abnormal test results, but further study and validation in a clinical setting are required.