Shawn Connolly

The effect of elevated fetal hemoglobin on hemoglobin A1c results: five common hemoglobin A1c methods compared with the IFCC reference method.

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.

Measurement of Hba1C in patients with chronic renal failure

BACKGROUND Carbamylated hemoglobin (carbHb) is reported to interfere with measurement and interpretation of HbA(1c) 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 HbA(1c) measurements and compared HbA(1c) with glycated albumin (GA) in patients with and without renal disease to test if CRF causes clinically significant bias in HbA(1c) results by using 11 assay methods. Subjects included those with and without renal failure and diabetes. Each subjects estimated glomerular filtration rate (eGFR) was used to determine the presence and degree of the renal disease. A multiple regression model was used to determine if the relationship between HbA(1c) results obtained from each test method and the comparative method was significantly (p<0.05) affected by eGFR. These methods were further evaluated for clinical significance by using the difference between the eGRF quartiles of >7% at 6 or 9% HbA(1c). The relationship between HbA(1c) 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 HbA(1c) was approximately 1.5% HbA(1c) lower in patients with renal failure. CONCLUSIONS Although most methods can measure HbA(1c) accurately in patients with renal failure, healthcare providers must interpret these test results cautiously in these patients due to the propensity for shortened erythrocyte survival in renal failure.

Higher degree of glycation of hemoglobin S compared to hemoglobin A measured by mass spectrometry: Potential impact on HbA1c testing

BACKGROUND Glycated hemoglobin (GHb), reported as HbA1c, is used as marker of long-term glycemia for diabetic patients. HbA1c results from boronate affinity methods are generally considered to be unaffected by most hemoglobin variants; this assumes comparable glycation of variant and non-variant (HbAA) hemoglobins. In this report, glycation of HbA beta chain (βA) and HbS beta chain (βS) for the most common Hb variant trait (HbAS) are examined. METHODS We analyzed 41 blood samples from subjects with HbAS, both with and without diabetes. Using LC-MS, ratios of glycated HbS to glycated HbA were determined by comparison of areas under the curves from extracted ion chromatograms. RESULTS Glycation of βS chains was significantly higher (p<0.001) than βA chains; this difference was consistent across subjects. Total (α+β) glycated HbAS was theoretically estimated to be ~5% higher than glycated HbAA. CONCLUSION This novel mass-spectrometric approach described allows for relative quantification of glycated forms of βS and βA. Although βS glycation was significantly higher than that of βA, the difference in total glycation of HbAS versus HbAA was smaller and unlikely to impact clinical interpretation of boronate affinity HbA1c results. These data support the continued use of boronate affinity to measure HbA1c in patients with HbAS.

Human C-peptide Quantitation by LC-MS Isotope-Dilution Assay in Serum or Urine Samples

In this communication we report a simple and efficient approach to C-peptide quantitation using isotope dilution mass-spectrometry analysis. The method facilitates quantitation of C-peptide levels at least one order of magnitude lower compared to concentration levels achieved with an IDA method reported previously. The improvement was due to more intensive sample preparation procedure that, in turn, makes it possible to increase the sample load without a corresponding increase in matrix effects. We also show the results of a comparison study with a second laboratory using a similar previously reported method for C-peptide quantitation.

Isotope dilution assay in peptide quantification: The challenge of microheterogeneity of internal standard

Isotope dilution analysis allows quantitation of elements and different compounds in complex mixtures. The quantitation is based on a known amount of reference material (internal standard, IS) added to a sample that makes the result critically dependent on the value assigned to the standard. In the case of peptides, IS concentration is determined by nitrogen and amino acid analysis while purity is normally assessed by methods such as chromatography or electrophoresis that might not be able to detect many possible amino acid modifications, either naturally occurring or chemically induced. Microheterogeneity of the IS, if it is not accounted for when assigning a reference value to the standard, results in highly overestimated values in target analyte quantitation. In this viewpoint article, we illustrate the problem of internal standard microheterogeneity by analyzing synthetic human C‐peptide labeled analogs.

Validation of the Use of Trinity Biotech ultra2 as a Comparative Method for Hemoglobin A1c Measurements in the Presence of HbE and HbD-Punjab Traits

To the Editor: The presence of hemoglobin variants can cause interferences with some Hemoglobin A1c (Hb A1c)1 methods. Boronate affinity chromatography is often used as the comparative method for hemoglobin interference studies, as it is generally assumed to be unaffected by most hemoglobin variants since total glycohemoglobin is measured regardless of hemoglobin species. We previously validated the use of the Trinity Biotech ultra2 boronate affinity HPLC as a comparative method for assessing interference from HbS and HbC traits (1). Here, we validate the use of the ultra2 as a comparative method for HbE trait (HbAE) and HbD-Punjab trait (HbAD) interference studies by comparing ultra2 Hb A1c results from samples with these variants with those of the IFCC HPLC–capillary electrophoresis (CE) reference method for Hb A1c (IFCC RM). The IFCC RM measures the β chain N-terminal glycated and nonglycated hexapeptides after a proteolytic digestion (2). Since the …

Implementing a Reference Measurement System for C-Peptide: An Addendum

To the Editor: In a recent study by Little et al. (1), the story of C-peptide standardization was left somewhat uncertain with the problem of 2 reference methods providing different C-peptide concentrations. Although very well correlated ( r 2 = 0.986), there was a bias of approximately 20% between the Diabetes Diagnostic Laboratory (DDL)1 method (operated in 2 different laboratories in the US) and the National Metrology Institute of Japan (NMIJ; y = 0.7824x − 0.0202). There were differences in the procedures and in the labeled internal standards (ISs). The NMIJ method was traceable to the NMIJ Certified Reference Material (6901-b) (2), whereas the DDL method was traceable to the IS developed in Dr. Steins Laboratory in …