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Clinical Chemistry and Hematology Laboratories

Clinical Chemistry: Blood pH and Gases

• Blood pH and Gases Proficiency Testing Database

This program monitors the performance of approximately 300 participating laboratories for three analytes: pH, Pco₂ and Po₂. Cassettes containing five ampules of buffered material are submitted to the laboratories three times per year for analysis.

CATEGORY DESCRIPTION

Laboratories performing measurement of blood pH, Pco₂, and/or Po₂ should hold a permit in Blood pH and Gases.

SOURCE OF SAMPLES

For blood pH, Pco₂, Po₂ commercially prepared perfluorocarbon or aqueous based specimens are used.

QUALITY CONTROL OF SAMPLES

Samples are distributed at ambient temperature. Volunteer laboratories in remote locations (including central reference laboratories in the Federal Republic of Germany, and the People's Republic of China) participate as volunteers in our program and monitor stability in long distance shipments. Specimens returned from laboratories are assayed upon return. Accelerated lability studies (monitoring samples at 20^oC and 37^oC) are also conducted. Specimens are assayed within our laboratory for tested analytes from representative vials to assess sample-to-sample variability. Unlike lyophilized specimens, liquid specimens exhibit minimal sample-to-sample variability. Specimens are prepared under sterile conditions minimizing deterioration due to potential bacterial contamination.

SAMPLE VALIDATION

The following acceptable performance criteria are used for sample validation:

ANALYTE	TARGET VALUE
Blood gas Po2	± 3 SD
Blood gas Pco2	± 5 mmHg or ± 8%(whichever is greater)
pH	± 0.04

TARGET VALUES

Target values are calculated by the mean of all participant responses after removal of outliers (those responses > ±3 SD from the original mean). Where available, target values are established, or verified, by reference methods or weighed-in values. Comparative method or "peer group" targets are used when it is demonstrated that specific methods demonstrate a bias with a proficiency specimen that is not observed with patient specimens.

GRADING

Grading for Blood pH and Gases is performed as follows:

Number of acceptable responses for the analyte   x 100	= Total Score
Number of challenges for the analyte

Number of acceptable responses for all challenges x 100	= Testing Event Score
Total number of all challenges

RESOLVING PROBLEMS

Technical, scientific, or administrative problems associated with testing in this specialty/subspecialty should be directed to the appropriate contact people listed above. The problem is identified as either a transcription, pre-analytical or analytical error. The results in question as well as previous data submitted by the laboratory and all participant data are reviewed. Based on current proficiency testing experiences, in many instances, the problem can be resolved in the initial telephone call or correspondence. However, should further action be required, the following is initiated:

1. Self-check specimens are forwarded for repeat analysis.

2. Thorough review of the participant laboratory's previous testing experiences and within laboratory quality control.

3. Arrange for interlaboratory comparisons using patient specimens or alternative testing fluids.

4. If the problem continues, suggest consulting instrument service representative and/or manufacturer for input.

Based on current proficiency testing experiences, in many instances the problem is resolved with self-check samples or corrective maintenance performed by laboratory staff or the service representative. If proficiency testing specimens are not evaluated, proficiency testing reports include the notice "Not Evaluated" on the computer-generated report to inform participants. Critiques distributed to participant laboratories will further detail the instruments, proficiency specimens, reagent kit(s), analyte(s) or other variables involved. A thorough investigation on the nature of the matrix-associated problem, specimen stability, or method non-specificity will be undertaken. Possible matrix sensitivities of materials used will be examined [cf. Rej, R., Jenny, R. W., and Bretaudiere, J.P., Quality control in clinical chemistry: characterization of reference materials Talanta 31, 851-862 (1984)]. Based on current proficiency testing experiences with the specimens prepared by our laboratories, such occurrences are uncommon.