Background Carbamylated hemoglobin (carbHb) is reported to interfere with measurement and interpretation of HbA1c in diabetic patients with chronic renal failure (CRF). There is also concern that HbA1c may give low results in these patients due to shortened erythrocyte survival. Methods We evaluated the effect of carbHb on HbA1c measurements and compared HbA1c with glycated albumin (GA) in patients with and without renal disease to test if CRF causes clinically significant bias in HbA1c results using 11 assay methods. Subjects included those with and without renal failure and diabetes. Each subject’s estimated glomerular filtration rate (eGFR) was used to determine the presence and degree of renal disease. A multiple regression model was used to determine if the relationship between HbA1c results obtained from each test method and the comparative method were significantly (p<0.05) affected by eGFR. These methods were further evaluated for clinical significance using difference between the eGRF quartiles of >7% at 6 or 9% HbA1c. The relationship between HbA1c and glycated albumin (GA) in patients with and without renal failure was also compared. Results Some methods showed small but statistically significant effects of eGFR; none of these differences were clinically significant. If GA is assumed to better reflect glycemic control, then HbA1c was approximately 1.5% HbA1c lower in patients with renal failure. Conclusions Although most methods can measure HbA1c accurately in patients with renal failure, healthcare providers must interpret these test results cautiously in these patients due the propensity for shortened erythrocyte survival in renal failure.

Background: Previous studies have shown interference with HbA1c measurement from the 4 most common heterozygous Hb variants (HbAS, HbAE, HbAC, and HbAD) with some assay methods. Here we examine analytical interference from 49 different less common variants with 7 different HbA1c methods using various method principles. Methods: Hb variants were screened using the Bio-Rad Variant or Variant II beta thal short program, confirmed by alkaline and acid electrophoresis, and identified by sequence analysis. The Trinity ultra2 boronate affinity high-performance liquid chromatography (HPLC) method and Roche Tinaquant immunoassay were used as primary and secondary comparative methods, respectively, since these methods are least likely to show interference from Hb variants. Other methods included were the Tosoh G7 and G8, Bio-Rad D-10 and Variant II Turbo, Diazyme Enzymatic, and Sebia Capillarys 2 Flex Piercing. To eliminate any inherent calibration bias, results for each method were adjusted using regression verses the ultra2 with nonvariant samples. Each method’s calibration-adjusted results were compared and judged to be acceptable if within the 99% prediction interval of the regression line for nonvariant samples. Results: Almost all variant samples were recognized as such by the ion-exchange HPLC methods by the presence of abnormal peaks or results outside the reportable range. For most variants, interference was seen with 1 or more of the ion-exchange methods. Following manufacturer instructions for interpretation of chromatograms usually, but not always, prevented reporting of inaccurate results. Results: Laboratories must be cautious about reporting results when the presence of a variant is suspected.

Background Hemoglobin C, D Punjab, E or S trait can interfere with hemoglobin A1c (HbA1c) results. We assessed whether they affect results obtained with 12 current assay methods. Methods Hemoglobin AA (HbAA), HbAC, HbAD Punjab, HbAE and HbAS samples were analyzed on one enzymatic, nine ion-exchange HPLC and two capillary electrophoresis methods. Trinity ultra2 boronate affinity HPLC was the comparative method. An overall test of coincidence of least-squared linear regression lines was performed to determine if HbA1c results were statistically significantly different from those of HbAA samples. Clinically significant interference was defined as >7% difference from HbAA at 6 or 9% HbA1c compared to ultra2 using Deming regression. Results All methods showed statistically significant effects for one or more variants. Clinically significant effects were observed for the Tosoh G8 variant mode and GX (all variants), GX V1.22 (all but HbAE) and G11 variant mode (HbAC). All other methods (Abbott Architect c Enzymatic, Bio-Rad D-100, Variant II NU and Variant II Turbo 2.0, Menarini HA-8180T thalassemia mode and HA-8180V variant mode, Sebia Capillarys 2 and Capillarys 3) showed no clinically significant differences. Conclusions Several methods showed clinically significant interference with HbA1c results from one or more variants which could adversely affect patient care.

Hemoglobin A1c (HbA1c) is an important indicator of risk for complications in patients with diabetes mellitus. Elevated fetal hemoglobin (HbF) levels have been reported to interfere with results of some HbA1c methods, but it has generally been assumed that HbA1c results from boronate-affinity methods are not affected by elevated HbF levels. None of the previous studies used the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) reference method as the comparative HbA1c method. We, therefore, measured HbA1c in samples with normal and elevated HbF levels by several common assay methods and compared the results with those of the IFCC reference method.HbF levels of more than 20% artificially lowered HbA1c results from the Primus CLC 330/385 (Primus Diagnostics, Kansas City, MO), Siemens DCA2000 (Siemens Healthcare Diagnostics, Tarrytown, NY), and Tosoh 2.2+ (Tosoh Bioscience, South San Francisco, CA), but not the Bio-Rad Variant II (Bio-Rad Laboratories, Hercules, CA) and Tosoh G7. Physicians and laboratory professionals need to be aware of potential interference from elevated HbF levels that could affect HbA1c results, including those from boronate-affinity methods.

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