Use of CTX-I and PINP as bone turnover markers: National Bone Health Alliance recommendations to standardize sample handling and patient preparation to reduce pre-analytical variability

The National Bone Health Alliance (NBHA) recommends standardized sample handling and patient preparation for C-terminal telopeptide of type I collagen (CTX-I) and N-terminal propeptide of type I procollagen (PINP) measurements to reduce pre-analytical variability. Controllable and uncontrollable patient-related factors are reviewed to facilitate interpretation and minimize pre-analytical variability.

INTRODUCTION

The IOF and the International Federation of Clinical Chemistry (IFCC) Bone Marker Standards Working Group have identified PINP and CTX-I in blood to be the reference markers of bone turnover for the fracture risk prediction and monitoring of osteoporosis treatment. Although used in clinical research for many years, bone turnover markers (BTM) have not been widely adopted in clinical practice primarily due to their poor within-subject and between-lab reproducibility. The NBHA Bone Turnover Marker Project team aim to reduce pre-analytical variability of CTX-I and PINP measurements through standardized sample handling and patient preparation.

METHODS

Recommendations for sample handling and patient preparations were made based on review of available publications and pragmatic considerations to reduce pre-analytical variability. Controllable and un-controllable patient-related factors were reviewed to facilitate interpretation and sample collection.

RESULTS

Samples for CTX-I must be collected consistently in the morning hours in the fasted state. EDTA plasma is preferred for CTX-I for its greater sample stability. Sample collection conditions for PINP are less critical as PINP has minimal circadian variability and is not affected by food intake. Sample stability limits should be observed. The uncontrollable aspects (age, sex, pregnancy, immobility, recent fracture, co-morbidities, anti-osteoporotic drugs, other medications) should be considered in BTM interpretation.

CONCLUSION

Adopting standardized sample handling and patient preparation procedures will significantly reduce controllable pre-analytical variability. The successful adoption of such recommendations necessitates the close collaboration of various stakeholders at the global stage, including the laboratories, the medical community, the reagent manufacturers and the regulatory agencies.

Pioglitazone decreases postprandial accumulation of remnant lipoproteins in insulin-resistant smokers

BACKGROUND

Fasting hypertriglyceridaemia has been reported to occur commonly in cigarette smokers and is thought to increase cardiovascular disease (CVD) risk in these individuals. More recently, it has been suggested that an increase in non-fasting triglycerides, rather than fasting hypertriglyceridaemia, is an independent CVD risk factor.

METHODS

In this study, we divided 24 smokers into insulin-resistant (IR) and insulin-sensitive (IS) groups by determining their steady-state plasma glucose concentrations during the insulin suppression test and compared fasting and daylong postprandial accumulation of total triglycerides and remnant lipoprotein (RLP) concentrations, before and after 3 months of pioglitazone (PIO) administration.

RESULTS

The two groups were similar in age, body mass index, race and gender distribution, but differed dramatically in insulin sensitivity. Baseline fasting and postprandial triglyceride, RLP cholesterol and RLP triglyceride concentrations were significantly higher in the IR smokers (p=0.01 to <0.01). Insulin resistance [corrected] and both fasting and postprandial triglyceride and RLP triglyceride levels decreased significantly (p=0.05 to 0.01) [corrected] in PIO-treated IR smokers, without any significant increase in weight instead of insulin sensitivity and both fasting and postprandial triglyceride and RLP triglyceride levels decreased significantly (p = 0.05 to, 0.01) in PIO-treated IR smokers, without any significant increase in weight. [corrected]

CONCLUSIONS

The postprandial accumulation of RLP particles is increased in the IR subset of smokers and is likely to contribute to the increased CVD risk in these individuals. Furthermore, PIO administration provides a possible therapeutic approach to decreasing postprandial lipaemia and CVD risk in IR smokers who are unwilling or unable to stop smoking.

Lipoprotein risk factors for cardiovascular disease in patients with type 2 diabetes mellitus treated with oral antihyperglycaemic agents

AIMS

To compare lipoprotein risk factors for cardiovascular disease (CVD) in patients with type 2 diabetes mellitus (DM) treated with a sulphonylurea (SU) compound only, metformin (MET) only, or combined SU + MET.

METHODS

The study population consisted of 62 patients with type 2 DM, whose antihyperglycaemic treatment program had been stable for at least 3 months, divided into three groups: 26 patients in the SU group, 17 patients in the MET group and 19 patients in the SU + MET group. None of the patients were taking lipid-lowering drugs. Fasting venous blood samples were taken to measure concentrations of glucose, total cholesterol, triglycerides (TG), high-density lipoprotein-cholesterol (HDL-C), low-density lipoprotein-cholesterol (LDL-C) and remnant lipoprotein-cholesterol (RLP-C) as well as for determination of LDL particle diameter.

RESULTS

The three groups were similar in terms of age, gender, body mass index and fasting plasma glucose concentrations. Total cholesterol concentrations were significantly lower (p < 0.05 for trend) in those treated with SU + MET as compared with the other two groups. However, there were no significant differences between the three groups in their plasma concentrations of TG, LDL-C, HDL-C or RLP-C; furthermore, the proportion of individuals within each treatment group with small LDL particle diameter was also not different.

CONCLUSIONS

The lipoprotein profile of patients with type 2 DM, matched for level of fasting hyperglycaemia, was similar irrespective of treatment with SU alone, MET alone or SU + MET. Thus, we could not identify any changes in lipoprotein metabolism that could account for differences in risk of CVD as a function of treatment.

Remnant-like particle cholesterol and triglyceride levels of hypertriglyceridemic patients in the fed and fasted state

Potentially atherogenic triglyceride-rich lipoprotein (TRL) remnants can be isolated and quantitated as remnant-like particles (RLP), using an immunoaffinity gel containing specific anti-human apolipoprotein A-I (apoA-I) and apoB-100 monoclonal antibodies. The aim of the present study was to determine the relationship between postprandial changes in RLP levels and changes in total serum triglyceride (TG) in patients with different forms of hypertriglyceridemia (HTG). Three groups of patients were selected, having similarly elevated serum TG levels: a) HTG with TRL remnant accumulation (i.e., type III patients, n = 15, TG: 3.8 +/- 0.2 mm), b) HTG with increased LDL (i.e., type IIb patients, n = 15, TG: 3.7 +/- 0.2 mm), and c) HTG without evidence of remnant or LDL accumulation (i.e., type IV patients, n = 15, TG: 3.9 +/- 0.3 mm). Ingestion of a 45-g fat meal caused a significant increase in serum TG (30;-50%) in all patients. Mean serum TG levels of the three groups were not significantly different at 4 or 6 h after the meal. RLP cholesterol (C) and TG levels increased after the meal in all patients, but these postprandial increases were also not significantly different among groups. Type III patients had significantly higher (P < 0.01) levels of RLP-C and RLP-apoE in the fasted and fed state, and also had significantly higher RLP-C-to-serum TG ratios (P < 0.001) compared with the other groups. These results indicate that 1) RLP-C and RLP-TG levels are significantly increased in the fed versus fasted state in patients with elevated fasting TG levels; 2) patients with different forms of HTG, but similar TG levels, have similar postprandial increases in RLP-C and RLP-TG; and 3) type III patients have significantly elevated levels of RLP-C and RLP-apoE in both the fed and fasted state.

Ratio of remnant-like particle-cholesterol to serum total triglycerides is an effective alternative to ultracentrifugal and electrophoretic methods in the diagnosis of familial type III hyperlipoproteinemia

BACKGROUND

Familial type III hyperlipoproteinemia (HLP) is characterized by the presence of beta-migrating VLDL (beta-VLDL) and increased risk of cardiovascular disease. Assessment of plasma beta-VLDL is achieved by measuring the ratio of VLDL-cholesterol (VLDL-C) to total plasma triglycerides (TGs) or by detecting beta-VLDL in total VLDL. The objective of this study was to compare the clinical utility of the ratio of remnant-like particle-cholesterol (RLP-C) to total TGs with that of the current methods for diagnosing type III HLP.

METHODS

Detection of beta-VLDL by electrophoresis of VLDL was used to define type III HLP. Twenty-eight patients with type III HLP and 43 subjects lacking beta-VLDL were investigated. Fasting TG concentrations were >2.26 mmol/L in all subjects. Subjects were separated into three groups: group 1, serum total cholesterol </=5.18 mmol/L (n = 11); group 2, total cholesterol >5.18 mmol/L and TGs between 2.26 and 9.04 mmol/L (n = 51); and group 3, TGs >9.04 mmol/L (n = 9).

RESULTS

In group 2, a RLP-C-to-total TG molar ratio >/=0.23 (>/=0.10 when using mg/dL) and a VLDL-C-to-total TG molar ratio >/=0.69 (>/=0.30 when using mg/dL) correctly classified 94% and 90% of the subjects, respectively. The utility of the RLP-C-to-total TG ratio in diagnosing type III HLP decreased in patients in the other two groups.

CONCLUSION

When used in an appropriate target population, the RLP-C-to-total TG ratio is a convenient and effective alternative to ultracentrifugal and electrophoretic methods for diagnosing type III HLP.

Selection, validation, standardization, and performance of a designated comparison method for HDL-cholesterol for use in the cholesterol reference method laboratory network

BACKGROUND

Accurate and precise HDL-cholesterol (HDL-C) measurements are essential for effective application of National Cholesterol Education Program treatment guidelines. The Cholesterol Reference Method Laboratory Network (CRMLN) assists manufacturers of in vitro diagnostic products to establish traceability to the accuracy base. CRMLN sought to implement a designated comparison method (DCM) that overcomes the impracticalities of the expensive and labor-intensive reference method for HDL-C.

METHODS

CRMLN evaluated candidate DCMs and selected one that uses 50-kDa dextran sulfate with magnesium ions as the precipitation reagent followed by measurement of cholesterol by the CDC reference method. After validating the method, we transferred it to all CRMLN laboratories and successfully standardized it using CDC frozen serum reference materials. CRMLN laboratories participate in monthly performance evaluations.

RESULTS

CRMLN laboratories were able to meet a precision goal, as indicated by SD, of </=0.03 mmol/L (1 mg/dL) 94.4% of the time. They were able to meet a bias goal of </=0.05 mmol/L (2 mg/dL) for HDL-C <1.09 mmol/L (42 mg/dL) 97.3% of the time and a goal of </=3% for HDL-C >/=1.09 mmol/L (42 mg/dL) 95.6% of the time. CRMLN is working to further improve its performance by implementing a bias criterion of 0.03 mmol/L (1 mg/dL) for all HDL-C concentrations.

CONCLUSIONS

CRMLN selected, validated, standardized, and implemented a DCM for HDL-C that is accurate, robust, transferable, and practical. The DCM is being used to assist manufacturers in calibrating their products so that ultimately, clinical laboratories using the products will more accurately measure HDL-C.

Evaluation of an immunoseparation method for quantitative measurement of remnant-like particle-cholesterol in serum and plasma

Substantial evidence indicates that triglyceride-rich lipoprotein remnants are atherogenic. Additional research has, however, been limited by available methods for separation and quantification of remnants. We have evaluated an immunoseparation assay developed to measure cholesterol in remnant-like particles (RLP-C). This method uses monoclonal antibodies to human apolipoproteins B-100 and A-I to remove most of the apolipoprotein B-100-containing lipoproteins (namely LDL and nascent VLDL) and apolipoprotein A-I-containing lipoproteins (namely chylomicrons and HDL), leaving behind a fraction of triglyceride-rich lipoproteins, including chylomicron and VLDL remnants, both of which are enriched in apolipoprotein E. Cholesterol in the unbound fraction is measured with a sensitive enzymatic assay. The RLP-C concentration was highly correlated with total triglyceride-rich lipoproteins (sum of VLDL-cholesterol and IDL-cholesterol) separated by ultracentrifugation and by polyacrylamide gel electrophoresis (r = 0.86 and 0.76, respectively). The within-run and run-to-run imprecision (CV) of the assay was approximately 6% and 10%, respectively. The assay was not affected by hemoglobin up to 5000 mg/L (500 mg/dL), bilirubin up to 342 mmol/L (20 mg/dL), glucose up to 67 mmol/L (1200 mg/dL), or ascorbic acid up to 170 mmol/L (3.0 mg/dL). In 726 subjects (men, n = 364; women, n = 362) in the US, the 75th percentiles of RLP-C concentration were 0.17 mmol/L (6.6 mg/dL) and 0.23 mmol/L (8.8 mg/dL) in sera obtained after overnight fasting or randomly, respectively. A group of 151 patients from nine US centers and one Canadian center with coronary artery atherosclerosis established by angiography had higher median RLP-C concentrations than 302 gender- and age-matched controls (P <0.05). We conclude that the RLP-C assay compares favorably to ultracentrifugation and electrophoresis and provides a convenient and economical approach to measure triglyceride-rich lipoprotein remnants in routine clinical laboratories.

Point: status of lipid and lipoprotein standardization

Cholesterol and triglyceride standardization procedures have been used extensively and continuously since the 1950s. Definitive and Reference Methods, as well as primary and secondary standards, have been developed and maintained as the basis for evaluating the accuracy of results by various methods in many laboratories. But, although standardization efforts for apolipoprotein A-I and B measurements have been reported in detail in the scientific literature, much less has been reported in the area of total and lipoprotein cholesterol and triglyceride standardization efforts. Standardized cholesterol and triglyceride concentrations, determined in multiple large epidemiological and clinical studies, have been instrumental to the National Cholesterol Education Program panels that have assessed the lipoprotein values associated with risk of coronary disease, and have determined the cutpoints that are now used extensively by physicians to guide diagnosis and treatment of individual patients.

The Women's Health Trial Feasibility Study in Minority Populations: design and baseline descriptions

The Women's Health Trial: Feasibility Study in Minority Populations (WHT:FSMP), a randomized trial of 2208 women, was conducted to investigate three questions. First, can women from minority and low-socioeconomic-status populations be recruited in numbers sufficient to evaluate a dietary intervention designed to lower fat intake. Second, the efficacy of a low fat, increased fruit/vegetable/ grain product intervention for reducing fat consumption. Third, will participation in the intervention lower plasma cholesterol and estradiol levels relative to the controls. The baseline results showed that an adequate number of minority and low SES women could be recruited to test the study hypotheses. A diverse study population of postmenopausal women consuming a high fat diet was recruited: 28% of participants were Black, 16% were Hispanic, 11% had less than a high school level of education, and 15.5% had household incomes of < $15,000.

Multicenter evaluation of a patient-administered test for blood cholesterol measurement

BACKGROUND

In order to assess accuracy of a newly developed, noninstrumented, self-administered fingerstick test that measures cholesterol levels in whole blood, the AccuMeter Cholesterol Self-Test was evaluated for home-use by untrained consumers in a multicenter study.

METHODS

A total of 486 untrained adult volunteers of varying age, occupation, and educational background were recruited at four sites. Participants received written instructions provided in the kit, access to a telephone "800" number for additional help, and, if necessary, a short instructional video available to consumers on request. Fingerstick cholesterol results obtained by untrained volunteers were compared with paired venous serum results obtained by the Abell-Kendall cholesterol reference method. After application of exclusion criteria, 79.0% (384/486) of subjects had AccuMeter fingerstick results available for comparison with the reference method.

RESULTS

Results obtained with the AccuMeter test correlated well with the Abell-Kendall results (r = 0.91). There was a mean overall bias for the AccuMeter of -0.116 +/- 0.528 mmol/liter (-2.2%), with a mean absolute bias of 0.398 +/- 0.367 mmol/liter (7.6%). Biases at the National Cholesterol Education Program cutpoints of 5.20 and 6.20 mmol/liter were -2.2 and -2.5%, respectively. Subjects with high-risk total cholesterol values (> or = 6.20 mmol/liter) were correctly classified 80.0% of the time, with an additional 18.8% placed in the borderline category (5.20-6.20 mmol/liter); 1.2% were inappropriately placed in the desirable category. No subjects were placed in the high-risk category by the AccuMeter test if they had a desirable cholesterol value by the reference method, while 9.8% were placed in this category if they were in fact borderline.

CONCLUSIONS

This test appears to be a useful addition to available options in the effort to increase awareness of cholesterol as a heart disease risk factor. A large portion of untrained consumers were able to perform the AccuMeter Cholesterol Self-Test and obtain comparable results to the reference method. This test for the first time allows consumers to determine their own cholesterol values, with a reasonably good degree of accuracy.

Accurate direct determination of low-density lipoprotein cholesterol using an immunoseparation reagent and enzymatic cholesterol assay

Clinical laboratories currently estimate low-density lipoprotein cholesterol using the Friedewald formula, which requires fasting specimens and is subject to error with increasing triglyceride levels. We describe a rapid method for isolating low-density lipoproteins using the Direct LDL Immunoseparation Reagent for subsequent measurement of cholesterol by conventional assay. This method meets current guidelines for precision with within-run and run-to-run coefficients of variation of less than 3%. Results are in good agreement with the beta quantification reference method (Direct LDL-C = 1.03 [beta quantification] -0.06 mmol/L, [2.4 mg/dL] r = 0.980), there is minimal bias associated with increasing triglycerides or high-density lipoprotein cholesterol, and patient fasting is not required for accurate analysis. The Direct LDL Immunoseparation Reagent overcomes drawbacks of the Friedewald formula and appears to be suitable for accurate quantitation of low-density lipoprotein cholesterol in the routine laboratory.

Cholesterol in fingerstick capillary specimens can be equivalent to conventional venous measurements

Current interest in coronary heart disease and cholesterol has led to the development of a new generation of compact analysis systems designed for fingerstick whole blood measurement. Since reliable classification of patients based on national cut-points for serum cholesterol concentration requires accurate results, the question whether results from fingerstick capillary specimens are equivalent to those from conventional venous-derived serum specimens, the basis for the national cut-points, is germane. Earlier studies in the literature are contradictory, with fingerstick differences ranging from 9% low to 6% high. We developed guidelines for reliable fingerstick collection and, following these guidelines, achieved results that were comparable to results derived from concurrently collected venous serum specimens. Results measured either by an accurate, standardized enzymatic assay or by the AccuMeter, a new noninstrumented device, were in close agreement with serum results, ie, within 1% and 1.7%, respectively, suggesting that fingerstick measurements are appropriate for identifying individuals with elevated cholesterol levels and monitoring their treatment.

Modification of the dextran-Mg2+ high-density lipoprotein cholesterol precipitation method for use with previously frozen plasma

Although dextran-Mg2+ precipitation produces accurate and precise results for high-density lipoprotein (HDL) cholesterol in fresh plasma and serum, precipitation of frozen specimens with triglycerides &gt; 2.26 mmol/L (&gt; 200 mg/dL) is difficult. We developed a modification that dilutes thawed samples by 35% and increases dextran-Mg2+ reagent to 15% of sample volume. Standard precipitations were performed on 62 fresh EDTA-treated plasma specimens; supernatant solutions were analyzed fresh and after freezing. Standard and modified methods were also performed on thawed, paired plasmas. In specimens with triglycerides &lt; or = 2.26 mmol/L, HDL cholesterol results for all methods were similar. For triglycerides &gt; 2.26 mmol/L, however, bias and precision were significantly affected by freezing, and 38.5% of samples with standard precipitation required additional procedures to produce clear supernatant solutions. HDL cholesterol concentrations for thawed samples with standard precipitation were significantly greater than for fresh samples (P &lt; 0.02), but those for the modified method were not different from fresh samples, and only one specimen required additional steps to produce a clear supernate.

Modification of the dextran-Mg2+ high-density lipoprotein cholesterol precipitation method for use with previously frozen plasma

Although dextran-Mg2+ precipitation produces accurate and precise results for high-density lipoprotein (HDL) cholesterol in fresh plasma and serum, precipitation of frozen specimens with triglycerides > 2.26 mmol/L (> 200 mg/dL) is difficult. We developed a modification that dilutes thawed samples by 35% and increases dextran-Mg2+ reagent to 15% of sample volume. Standard precipitations were performed on 62 fresh EDTA-treated plasma specimens; supernatant solutions were analyzed fresh and after freezing. Standard and modified methods were also performed on thawed, paired plasmas. In specimens with triglycerides < or = 2.26 mmol/L, HDL cholesterol results for all methods were similar. For triglycerides > 2.26 mmol/L, however, bias and precision were significantly affected by freezing, and 38.5% of samples with standard precipitation required additional procedures to produce clear supernatant solutions. HDL cholesterol concentrations for thawed samples with standard precipitation were significantly greater than for fresh samples (P < 0.02), but those for the modified method were not different from fresh samples, and only one specimen required additional steps to produce a clear supernate.

Commercially available blood-gas quality controls compared with tonometered blood

We compared three commercially supplied blood-gas quality control solutions ("contrIL," "G.A.S.," and "Quantra") and tonometered whole blood under research and service conditions in four hospital laboratories. In some situations Quantra and tonometered blood were comparably sensitive to problems with blood-gas instrument malfunctions (e.g., hydraulics or temperature control) but the aqueous buffer-based materials were less sensitive. Within-day precision for all control materials was similar. The precision of pCO2 determinations in long-term studies was also similar for all control materials, as were pH determinations on commercial controls. For pO2 (especially at O2 < 50 mmHg), sample handling technique influenced the precision and accuracy of Quantra more than the other materials. The variability in pO2 determination with Quantra seems primarily to result from sensitivity in incubation temperature (3% change per degree C at 145 mmHg and 7% change per degree C at 43 mmHg). This study identifies some of the limitations of blood-gas control materials per se and some limitations related to specific blood-gas instruments that affect interpretation of results from them.

Commercially available blood-gas quality controls compared with tonometered blood

We compared three commercially supplied blood-gas quality control solutions ("contrIL," "G.A.S.," and "Quantra") and tonometered whole blood under research and service conditions in four hospital laboratories. In some situations Quantra and tonometered blood were comparably sensitive to problems with blood-gas instrument malfunctions (e.g., hydraulics or temperature control) but the aqueous buffer-based materials were less sensitive. Within-day precision for all control materials was similar. The precision of pCO2 determinations in long-term studies was also similar for all control materials, as were pH determinations on commercial controls. For pO2 (especially at O2 &lt; 50 mmHg), sample handling technique influenced the precision and accuracy of Quantra more than the other materials. The variability in pO2 determination with Quantra seems primarily to result from sensitivity in incubation temperature (3% change per degree C at 145 mmHg and 7% change per degree C at 43 mmHg). This study identifies some of the limitations of blood-gas control materials per se and some limitations related to specific blood-gas instruments that affect interpretation of results from them.

Use of equilibrated blood for internal blood-gas quality control

We have used equilibrated human blood for blood-gas quality control since 1970. In blood equilibrated 24 h after shedding, gas tensions are stable for 4 to 6 h at 0 to 4 degrees C; each control specimen is analyzed several times during that period to resolve malfunctions, etc. Three-fourths of all errors in gas-tension measurement detected with equilibrated blood were detected with the highest-tension controls. Equilibrated blood controls signal about one error every 14 d on each instrument. For more complete quality control, we supplement analysis of equilibrated blood with other sorts of controls, comparing results obtained by assaying each patient's specimen on two instruments being our most effective adjunct. Such comparisons have identified erroneous assays in 3.9% of the specimens tested. The magnitude of interinstrument discrepancies (random errors) have ranged from 9 to 100% of the appropriate determinations. We use control data derived from equilibrated blood analysis for special management purposes (evaluating instruments, quantitating micro- vs. macro-sampling discrepancies, and decreasing instrument-repair costs).

Use of equilibrated blood for internal blood-gas quality control

We have used equilibrated human blood for blood-gas quality control since 1970. In blood equilibrated 24 h after shedding, gas tensions are stable for 4 to 6 h at 0 to 4 degrees C; each control specimen is analyzed several times during that period to resolve malfunctions, etc. Three-fourths of all errors in gas-tension measurement detected with equilibrated blood were detected with the highest-tension controls. Equilibrated blood controls signal about one error every 14 d on each instrument. For more complete quality control, we supplement analysis of equilibrated blood with other sorts of controls, comparing results obtained by assaying each patient's specimen on two instruments being our most effective adjunct. Such comparisons have identified erroneous assays in 3.9% of the specimens tested. The magnitude of interinstrument discrepancies (random errors) have ranged from 9 to 100% of the appropriate determinations. We use control data derived from equilibrated blood analysis for special management purposes (evaluating instruments, quantitating micro- vs. macro-sampling discrepancies, and decreasing instrument-repair costs).

Proficiency testing for blood-gas quality control

We have conducted a voluntary, community blood-gas proficiency testing program, with use of tonometered human blood, for 32 analyzers located in 16 laboratories. Instruments initially showed inaccuracies as large as -30.8 to +17.3% for po(2), and -14.0 to +42.9% for pco(2), but inaccuracy and imprecision decreased in most laboratories during the program. For a typical 15-week period, mean group precision (CV) was 4.3 To 5.1% for po(2) from 6.92 to 33.3 Pa (52 to 250 mmHg), and 4.0 to 6.9% for pco(2) from 2.0 to 6.8 Pa (15 to 51 mmHg). This program can detect increasing imprecision or inaccuracy caused by analyzer deterioration, and can identify interlaboratory or interinstrument bias and problems not detected by participant quality-control programs. Participants have used the proficiency information in discussing data quality with clinicians, promoting internal control and maintenance programs, and justifying instrument purchases. We believe that proficiency-testing documentation of variability in blood-gas analysis may help to establish realistic patient-care protocols.

Proficiency testing for blood-gas quality control

We have conducted a voluntary, community blood-gas proficiency testing program, with use of tonometered human blood, for 32 analyzers located in 16 laboratories. Instruments initially showed inaccuracies as large as -30.8 to +17.3% for po(2), and -14.0 to +42.9% for pco(2), but inaccuracy and imprecision decreased in most laboratories during the program. For a typical 15-week period, mean group precision (CV) was 4.3 To 5.1% for po(2) from 6.92 to 33.3 Pa (52 to 250 mmHg), and 4.0 to 6.9% for pco(2) from 2.0 to 6.8 Pa (15 to 51 mmHg). This program can detect increasing imprecision or inaccuracy caused by analyzer deterioration, and can identify interlaboratory or interinstrument bias and problems not detected by participant quality-control programs. Participants have used the proficiency information in discussing data quality with clinicians, promoting internal control and maintenance programs, and justifying instrument purchases. We believe that proficiency-testing documentation of variability in blood-gas analysis may help to establish realistic patient-care protocols.