Proficiency Testing Materials Research Articles

Patterns of Dissimilarities Among Instrument Models in Measuring Po2, Pco2, and pH in Blood Gas Laboratories

To ascertain the degree of dissimilarities among blood gas and pH analyzer models of the same and different manufacturers in measurement of PO2, PCO2, and pH using fluorocarbon containing emulsion (FCE) proficiency testing material. Statistically and graphically analyze data from six recent proficiency testing surveys for the 20 more frequently used models of analyzers. Over a 2-year period, approximately 900 participants from blood gas laboratories in the United States analyzed similar ampules from each of 30 lots. Both graphic and statistical comparisons were used to demonstrate differences between manufacturers. For each of the four major manufacturers, comparisons revealed statistically significant differences not only for PO2, but also for PCO2 and pH. Additionally, comparison models within each of the three manufacturers (those with multiple models and > 15 instruments per model represented) disclosed statistically significant dissimilarities among models for each analyte in 115 of 153 model pairings. Previously reported tonometered blood differences among analyzer models for PO2 are qualitatively similar to the differences found in these same models in this FCE study. Model differences are important in research studies and may be clinically important in deciding abnormality, selecting oxygen therapy, or the treatment of patients with respiratory failure or severe respiratory alkalosis. To minimize the likelihood of misleading clinicians, laboratory directors should consider the degree of dissimilarity among blood gas analyzer models in current use and when changing instrumentation.

TUNA FISH (T-30) - A new proficiency testing material for the determination of As and Hg in seafood

The quality of the aquatic and marine environment can be monitored by the determination of pollutants in organisms living in this environment. Certified reference materials and well-organised proficiency tests are powerful means of ensuring a constant level of quality and verifying the correct application of standardised methods. The preparation of a tuna fish proficiency testing material for the evaluation of quality of As and Hg monitoring in seafood is described. Preparation and characterisation of the material as well as studies on its homogeneity and stability are described. Concentrations of 3.4 ± 0.2 mg/kg total arsenic and 2.91 ± 0.09 mg/kg total mercury have been determined as target values. Moreover indicative values for some trace elements (Cd, Cu, Ni, Pb, Sr) and some major constituents (Al, Br, C, Ca, Cl, Fe, H, K, Mg, N, Na, P, S, Si, Zn) have also been measured.

Reduced bovine hemoglobin solution evaluated for use as a blood gas quality-control material

We evaluated a new commercially available partially purified reduced bovine hemoglobin solution (RBHS) and a new tonometer for use in the quality control of blood gas analyzers. RBHS is manufactured in three different formulations, each corresponding to three different bicarbonate-buffering capacities and concentrations of total hemoglobin (ctHb). The P50 for each formulation of RBHS was determined to be as follows: 30.6 mmHg (4.08 kPa) for Level 1, 29.1 mmHg (3.88 kPa) for Level 2, and 28.2 mmHg (3.76 kPa) for Level 3. When RBHS and human blood samples were tonometered at three clinically significant values of PO2 and PCO2, the recovered values for PO2 and PCO2 in RBHS were comparable with those of the tonometered whole blood. Each level of RBHS also produced precise pH (SD < or = 0.006 pH units) and ctHb (SD = 1.0 g/L) values. In addition, when the temperature of a sample chamber was intentionally altered, the changes in RBHS blood gas values closely approximated the changes seen with human blood. RBHS shows more thermal sensitivity than either perfluorocarbon emulsions or aqueous buffers, which are currently being used as quality-control and proficiency testing materials.

Speciation of mercury in fish samples by solvent extraction, methyl-mercury reduction directly in the organic medium and cold vapour atomic absorption spectrometry

The extraction of CH3Hg+ as bromide from fish samples by chloroform and its direct determination in an organic medium by cold vapour atomic absorption spectrometry (CVAAS) is proposed. Parameters studied include the nature and concentration of the reductant and the acid stirring time. No matrix effect was observed. Inorganic Hg was determined in the residual aqueous phase by reduction with NaBH4. Spiking studies showed good recoveries of 102±2%. The procedure was applied to fish samples and the ratio between Hg as CH3Hg+ and total Hg was in the range 88–98%, usually found in the literature. The sum of the organic and inorganic Hg concentrations matched the total Hg value found by CVAAS after acid digestion. The detection limit (3σ) for the total analytical procedure was 25 ng of Hg (as CH3Hg+) per gram of wet sample. The proposed procedure was also applied to two proficiency testing materials and to a standard reference material and the summation of organic and inorganic Hg concentration values were in good agreement with the reference values, according to a student t test for a significance level of 99%, n= 5.

Assessing Precision and Accuracy in Blood Gas Proficiency Testing

Blood gas proficiency testing has focused on assessing the accuracy of measurement of each analyte (pH, PCO2) independently of each other. Recently, the American Thoracic Society-California Thoracic Society Blood Gas Proficiency Testing Survey distributed the same lot of ampules of proficiency testing material (a buffered fluorocarbon-containing emulsion) on three occasions within a 1-yr period, allowing us to assess the precision (reproducibility) of measurement of each analyte. Comparing 580 instruments of 13 models, we found that the precision of measurement of each analyte was positively correlated with the precision of measurement of each other analyte, and the correlation of precision between models was much stronger than precision between the individual instruments. We also found correlation of precision of each analyte with two targets for accuracy: (1) the all-instrument mean and (2) the model-specific means. Correlations were higher with the model-specific means. These findings suggest: (1) that features unique to design of each model are important in the precision of measurement of these ampules, and (2) that it would be informative to include measurements of precision with linked and cumulative ratings of analyte accuracy in proficiency testing rating systems.

Assessing Precision and Accuracy in Blood Gas Proficiency Testing

Blood gas proficiency testing has focused on assessing the accuracy of measurement of each analyte (pH, PCO2) independently of each other. Recently, the American Thoracic Society-California Thoracic Society Blood Gas Proficiency Testing Survey distributed the same lot of ampules of proficiency testing material (a buffered fluorocarbon-containing emulsion) on three occasions within a 1-yr period, allowing us to assess the precision (reproducibility) of measurement of each analyte. Comparing 580 instruments of 13 models, we found that the precision of measurement of each analyte was positively correlated with the precision of measurement of each other analyte, and the correlation of precision between models was much stronger than precision between the individual instruments. We also found correlation of precision of each analyte with two targets for accuracy: (1) the all-instrument mean and (2) the model-specific means. Correlations were higher with the model-specific means. These findings suggest: (1) that features unique to design of each model are important in the precision of measurement of these ampules, and (2) that it would be informative to include measurements of precision with linked and cumulative ratings of analyte accuracy in proficiency testing rating systems.

The significance of matrix effects on the measurement of lactate dehydrogenase (LD) activity using kodak dry slide technology in the ontario laboratory proficiency testing program

A recent lactate dehydrogenase (LD) survey of the Laboratory Proficiency Testing Program (LPTP) of Ontario showed interlaboratory coefficients of variation ranging from 6.5% to 40% for five lyophilized vials on the 12 Kodak analyzers. All the LPTP survey samples had similar protein and LD isoenzyme electrophoretic patterns which remained unchanged after reconstitution and storage for 5 days at 4 degrees C, although the total LD activities fell. Four Ektachem 700 analyzers were subsequently tested using LPTP material and no difference in LD activity between instruments or between two LD slide lot numbers was shown. Generation 9 slides gave higher LD activities than generation 10 on all the reconstituted lyophilized proficiency testing samples. There was no significant difference between slide generations when 19 liquid human sera were analyzed, indicating that the variability on LPTP samples was due to a matrix effect. Definition of the matrix effect of lyophilized proficiency testing material is essential before any proficiency testing program can use such material to reflect analytical performance on patient specimens.

Performance Compared By Shift

The day and evening clinical laboratory staffs of 50 Pennsylvania hospitals were presented with identical proficiency testing materials for analysis. The materials tested the ability of the shifts to duplicate results for glucose, BUN, sodium, potassium, chloride, prothrombin time, activated partial thromboplastin time, CSF Gram stain, and a differential blood film. A significant difference (P>.05) was found for the Gram stain evaluation. Of those factors considered to explain this difference, only years of technical experience were shown to be significant.

Evaluation of blood gas quality control and proficiency testing materials by tonometry.

Because of consistent differences found by other investigators and by us, we systematically tonometered, sampled, and measured PO2 and PCO2 concentrations of fresh blood, plasma, and several commercial quality control materials in three models of semiautomated blood gas machines. We found no significant differences between materials or machines for PCO2 between 25 to 72 mm Hg. For tonometered PO2 of approximately 25 to 100 mm Hg, the measured PO2 concentrations were accurate for blood, high for materials with hemoglobin or fluorocarbon (high O2 capacity), and very high for other materials (low O2 capacity). A low O2 capacity material tonometered to a PO2 of 0 mm Hg gave very high values in semiautomated machines and gave correct values only when injected repeatedly without interrupting rinse cycles into a manual machine. These findings indicate significant contamination of blood gas machines with fluids other than the sample so that low O2 capacity quality control materials are inadequate for proficiency testing at degrees of PO2 below 100 mm Hg.