Trefor Higgins

Variation in the Frequency of Hemoglobin A1c (HbA1c) Testing: Population Studies Used to Assess Compliance with Clinical Practice Guidelines and Use of HbA1c to Screen for Diabetes

Background: The volume of hemoglobin A1c (HbA1c) testing has increased dramatically over the past decade and few studies have attempted to determine how the test is used. The goals of this study were to evaluate the frequency of HbA1c testing in regional populations to assess the extent of screening for diabetes and to determine if the HbA1c testing intervals of known diabetic patients were consistent with clinical practice guidelines. Methods: Two years of HbA1c results were extracted from laboratory information systems in four regions of the province of Alberta that represent urban, mixed urban-rural, and rural populations. HbA1c testing frequencies and the proportions of nondiabetic patients undergoing HbA1c tests were derived. Results: Approximately 60% of HbA1c tests in each region were done on patients who had only a single test during the 2-year interval. Testing of nondiabetic patients accounted for 24% of HbA1c tests and varied by region. While the cumulative frequency distributions of HbA1c test intervals resembled each other, detailed analyses of the frequency distributions depicted broad multimodal peaks and regional variations that suggest a great deal of heterogeneity among practices. The most common HbA1c testing interval was 3 months ± 3 weeks in each region and is consistent with the 3-month test interval target in a clinical practice guideline. Conclusions: HbA1c testing is being performed on a substantial proportion of nondiabetic patients. On average, patients with diabetes in Alberta receive 1.5 HbA1c tests per year. However, we observed regional differences in the frequency of testing and variation in compliance with clinical practice guidelines.

HbA1c — An analyte of increasing importance

Since the incorporation in 1976 of HbA(1c) into a monitoring program of individuals with diabetes, this test has become the gold standard for assessment of glycemic control. Analytical methods have steadily improved in the past two decades, largely through the efforts of the National Glycohemoglobin Standardization program (NGSP). The new definition of HbA(1c) and the introduction of an analytically pure calibrator have increased the possibility for greater improvements in analytical performance. Controversies exist in the reporting of HbA(1c). The use of HbA(1c) has expanded beyond the use solely as a measure of glycemic control into a test for screening and diagnosing diabetes. With improvements in analytical performance, the effects of demographic factors such as age and ethnicity and clinical factors such as iron deficiency have been observed. In this review, the history, formation, analytical methods and parameters that affect HbA(1c) analysis are discussed.

Analytical evaluation of the Bio-Rad Variant II automated HbA1C analyzer

OBJECTIVES To evaluate the analytical performance of the Bio-Rad Variant II HbA(1C) analyzer (a completely automated system for the quantification of glycohemoglobin [HbA(1C)] in blood). DESIGN AND METHODS The analytical parameters of precision, linearity and analytical range were assessed and HbA(1C) results from the Variant II were compared to HbA(1C) results from the Bio-Rad Variant (a method certified by the National Glycohemoglobin Standardization Program). The effect of a variety of hemoglobin variants on HbA(1C) obtained on the system was investigated. RESULTS Total imprecision was less than 5% and the results compared well with those from an established method. The method has a wide analytical range with no carryover between specimens. CONCLUSION The HbA(1C) method on the Variant II gives acceptable analytical performance.

Seasonal Variation in Hemoglobin A1c: Is It the Same in Both Hemispheres?

Introduction: There are several reports from locations in the northern hemisphere of seasonal variation in hemoglobin A1c (HbA1c) levels with higher values noted in the cooler months. The variation has been attributed to holiday seasons, temperature differences, and changes in diet. This article describes the seasonal variation in both hemispheres and in a country on the equator with minimal temperature variation. Methods: The mean and median HbA1c by month was calculated for a maximum of 2 years for HbA1c data from the different locations: Edmonton and Calgary, Canada; Singapore; Melbourne, Australia; and Marshfield, Wisconsin. The mean monthly temperature for each location was found from available meteorological information. Results: In both northern and southern hemispheres, the HbA1c was higher in cooler months and lower in the warmer months. In Singapore, where there is minimal temperature variation, there is also minimal variation in HbA1c values over the year. The difference in HbA1c over a year appears to be related to the difference in temperature. Conclusion: Hemoglobin A1c is higher in cooler months and lower in the warmer months in both hemispheres. In a country with minimal monthly temperature variation, there is only minimal variation in HbA1c values through the year. In all locations, the mean and median HbA1c declined over the study period, possibly due to better glycemic control of patients with diabetes or an increase in use of HbA1c as a screening test for diabetes or a combination of both.

The use of serial patient blood gas, electrolyte and glucose results to derive biologic variation: a new tool to assess the acceptability of intensive care unit testing.

Abstract Background: Most estimates of biologic variation (sb) are based on periodically acquiring and storing specimens, followed by analysis within a single analytic run. We demonstrate for many intensive care unit (ICU) tests, only patient results need be statistically analyzed to provide reliable estimates of sb. Methods: Over 11 months, approximately 28,000 blood gas measurements (including electrolyte panels and glucose) were performed on one of two Radiometer ABL800 FLEX analyzers (Radiometer, Copenhagen, Denmark) from 1676 ICU patients. We tabulated the measurements of paired intra-patient blood samples drawn within 24 h of each other. After removal of outliers, we calculated the standard deviations of duplicates (SDD) of the intra-patient pairs grouped in 2-h intervals: 0–2 h, 2–4 h, 4–6 h, … 20–22 h and 22–24 h. The SDDs were then regressed against the time intervals of 2–14 h; extrapolation to zero time represents the sum of sb and short-term analytic variation (sa). Results: Substitution of experimentally derived analytic error permitted the calculation of coefficient of variation (biologic) (CVb) (100 sb/mean): pH, 0.3%; pCO2, 5.7%; pO2, 13%; Na+, 0.6%; K+, 4.8%; Cl–, 0.8%; HCO3–, 3.2%; iCa++, 2.4%; and glucose, 10.3%. The CVb of the electrolytes very closely matches the lowest estimates obtained in the usual manner. Conclusions: Derivation of the ratio of biologic to analytic variation indicates that the ABL800 is extremely suitable for ICU testing. This analysis should be extended to other point of care instrument systems. Clin Chem Lab Med 2010;48:1447–54.

Comparison of two methods for the quantification and identification of hemoglobin variants.

BACKGROUND The Sebia Capillarys 2, a capillary electrophoresis method, was compared to a high performance liquid chromatography (HPLC) and electrophoresis at alkaline and acid pH for the presumptive identification and quantitation of hemoglobin variants. METHODS The concordance of hemoglobin variant identification on the Sebia Capillarys 2 with the combination of HPLC and electrophoresis at alkaline and acid pH was evaluated by analyzing samples on both systems. The quantification, expressed as % of total hemoglobin, of the common hemoglobin variants on the Capillarys 2 and the Bio Rad VARIANT II beta thalassemia methods were compared. RESULTS The % hemoglobin variant results for the two methods were similar for HbS and slightly different for HbC and D Punjab and significantly different for HbE. The Sebia Capillarys 2 correctly identified a number of hemoglobin variants. CONCLUSION The Sebia Capillarys 2 is suitable for the presumptive identification and quantification of hemoglobin variants producing results comparable with existing HPLC and electrophoresis methods.

Quantification of HbA 2 in Patients With and Without β-Thalassemia and in the Presence of HbS, HbC, HbE, and HbD Punjab Hemoglobin Variants Comparison of Two Systems

We studied whether problems quantifying hemoglobin A(2) (HbA(2)) could be resolved by using capillary electrophoresis. HbA(2) was quantified on whole blood samples from patients with and without beta-thalassemia trait and patients heterozygous for HbE, HbS, HbC, and HbD Punjab using the VARIANT II beta-thalassemia (Bio-Rad, Hercules, CA) and Capillarys 2 (Sebia, Norcross, GA). HbA(2) results in patients with and without beta-thalassemia trait were lower with the Capillarys 2 system. Reasonable HbA(2) results were obtained for patients with HbD Punjab and HbE traits on the Capillarys 2. HbA(2) results for patients with HbS, heterozygous and homozygous, were similar by both methods. Interference due to coelution for HbA(2) results for patients with HbC trait was noted on the Capillarys 2. Between-day imprecision on the VARIANT II is less than that for the Capillarys 2 system. The Capillarys 2 is superior to the VARIANT II for quantifying HbA(2) in the presence of HbE and HbD Punjab traits. The Capillarys 2 offers only slight advantages over the VARIANT II for quantifying HbA(2) in the presence of heterozygous and homozygous HbS. The Capillarys 2 gives inferior HbA(2) results for patients with HbC trait.

Comparison of lactate, bilirubin and hemoglobin F concentrations obtained by the ABL 700 series blood gas analyzers with laboratory methods

OBJECTIVE To compare lactate, bilirubin and Hemoglobin F concentrations obtained on ABL 700 series blood gas analyzers with those from laboratory methods. DESIGN AND METHOD Pooled neonatal plasma, cord blood and adult plasma samples were used for comparison of bilirubin, hemoglobin F and lactate concentrations respectively. RESULTS Results obtained on the ABL 700 series compared favorably (Deming regression slopes 0.97-1.13) with those from laboratory methods. For lactate ABL (y) = 1.13 Vitros (x) -0.43 with a CI (slope) of 1.10 to 1.16, CI (int) of -0.61 to -0.28. For hemoglobin F ABL(y) = 1.11 Variant (x) -8.0 with a CI (slope) of 0.88 to 1.33, CI (int) of -25.3 to 9.3. The three bilirubin comparisons are as follows: 1) Unistat (y) = 1.10 Vitros (x) -16.12 with CI (slope) of 1.06 to 1.14 and CI (int) of -25.3 to -6.9. 2), ABL (y) = 0.97 Vitros(x) -10.16 with CI (slope) of 0.94 to 1.00 and CI (int) of -17.6 to 2.73) Unistat (y) = 1.14 (x)-4.58 with CI (slope) of 1.09 to 1.18 and CI (int) of -13.6 to 4.5. CONCLUSION The ABL 700 series gave comparable results for lactate, bilirubin and hemoglobin F with laboratory methods and may be used in patient care.

Comparison of hemoglobin A1C results by two different methods on patients with structural hemoglobin variants.

OBJECTIVES The objective was to compare hemoglobin A1C (HbA1C) results obtained by two methods based on different analytical principles for individuals with a structural hemoglobin variant. DESIGN AND METHODS Hemoglobin A1C results were obtained using the Bio-Rad Variant (based on cation exchange chromatography) and the Bayer DCA 2000 (based on an immunological reaction) on individuals with a structural hemoglobin variant. The identity of the hemoglobin variant was confirmed by high pressure liquid chromatography (HPLC) and electrophoresis. RESULTS Hemoglobin A1C results obtained by the two methods on individuals with S, C, D, and E trait were in close agreement. CONCLUSION The Bio-Rad Variant and Bayer DCA 2000 produce equivalent hemoglobin A1C results on patients with S, C, and E trait. With appropriate correction, correlation of hemoglobin A1C results from the Bio-Rad Variant for individuals with D trait was good (r = 0.927). Glycohemoglobin results obtained by the two methods for some unusual structural hemoglobin variants were in close agreement.

Total hCG tests

INTRODUCTION There are 12 types of automated total hCG tests sold today, the Abbott Architect, Abbott AxSym, the Beckman Access 2. Beckman DxI 800, the Ortho Vitros EciQ, Roche Elecsys hCG+β, Siemens ACS180, Siemens Centaur, Siemens Dimension, Siemens Immulite and Siemens Stratus, and the Tosoh A1A. All tests claim to be total hCG tests but do not define what total means. Total hCG test needs to detect all hCG variants in order to be used for all hCG test clinical applications. Here we assess this ability. METHODS Coded samples of pure hCG, nicked hCG, hyperglycosylated hCG, nicked hCG missing C-terminal peptide, nicked hyperglycosylated hCG, asialo hCG, hCGβ, nicked hCGβ and β-core fragment were tested blindly in serum and urine at 10 independent laboratories. RESULTS While the Siemens Immulite total hCG test detected 8 of 9 hCG variant standards, other assays poorly detected important determinants such as nicked hCG missing the C-terminal peptide, β-core fragment, hyperglycosylated hCG, nicked hCG, asialo hCG, and hCGβ. Four assay appropriately detected 4 of 9 variants, 2 assays detected 3 of 9, 4 assays detected 2 of 9 and 1 assay only appropriately detected 1 of 7 hCG variants. DISCUSSION Care is needed in selecting a total hCG test. The Siemens Immulite tests performed best at detecting all the hCG variants making it appropriate for all applications. Nine assays had limited applications, 3 of the assays were appropriate for advanced pregnancy testing only.