Use of Continuous Glucose Monitoring Leads to Diagnosis of Hemoglobin C Trait In a Patient with Discrepant Hemoglobin A1C and Self-Monitored Blood Glucose

Abstract

Objective: Hemoglobin A1c (HbA1c) is a useful tool for the diagnosis and management of diabetes mellitus and generally an excellent marker of overall glycemic control for the preceding 8 to 12 weeks; however, the test is not without its pitfalls. A suspicion of falsely high or low HbA1c should prompt clinicians to evaluate for possible causes. Here, we present the novel use of continuous glucose monitoring (CGM) in a case of a 49-year-old African American woman with discrepant HbA1c and selfmonitored blood glucose (SMBG). CGM data suggested that the HbA1c values were falsely elevated, and subsequent evaluation led to a diagnosis of hemoglobin C (HbC) trait.Methods: Case identified is described. Point-of-care (POC) and central laboratory HbA1c were measured on the Bayer DCA 2000 and Bio-Rad Variant II Turbo ionexchange high-performance liquid chromatography platforms, respectively. Results:The patient had an elevated POC HbA1c of 10.8% (95 mmol/mol) and a central laboratory HbA1c of 9.2% (77 mmol/mol). The patient's glucose meter measured an average glucose of 138 mg/dL. The Freestyle LibrePro professional CGM was used to investigate the reliability of the patient's SMBG and showed an average glucose of 165 mg/dL. An investigation into potential causes for falsely elevated HbA1c revealed a previously undiagnosed HbC trait.Conclusion: CGM is a valuable tool to assess HbA1c and SMBG discordance and to guide subsequent diabetes management. Our results suggest that the HbA1c may have been overestimated in our patient due to HbC trait; therefore, results must be interpreted with caution. (AACE Clinical Case Rep. 2019;5:e31-e34) Abbreviations: CGM = continuous glucose monitoring; HbA1c = hemoglobin A1c; HbC = hemoglobin C; HPLC = highperformance liquid chromatography; POC = point-ofcare; SMBG = self-monitored blood glucose

Level of Agreement and Correlation Between the Estimated Hemoglobin A1c Results Derived by Continuous or Conventional Glucose Monitoring Systems Compared with the Point-of-Care or Laboratory-Based Measurements: An Observational Study

“…Thus, ADA currently considers CGM a valuable part of diabetes self-management and the standard of care for diabetic patients treated with intensive insulin therapy [ 30 ]. However, reports have shown a discordance between the HbA1c data measured by CGM compared to the standard laboratory HbA1c [ 18 – 21 ]. The exact reasons for this discrepancy are unknown [ 31 ].…”

“…Both SMBG and CGM have significant evidence supporting their efficacy in promoting better long-term glycemic control [ 17 ]. However, previous reports have shown a discordance between the glucose monitoring index (GMI) derived by isCGM and estimated average glucose (eAG) derived by conventional SMBG system with the standard laboratory HbA1c [ 18 – 21 ]. The potential discrepancies between laboratory and GMI derived by CGM devices are caused by estimated HbA1c being calculated through the average glucose and correlated with time in range, which is the relative time spent in a range of normal blood glucose [ 22 ].…”

A View Beyond HbA1c: Role of Continuous Glucose Monitoring

“…HbA1c represents the percentage of circulating hemoglobin that is glycated. Glycation is a non-enzymatic process and is a measure of glucose levels over time [ 8 ]. As a biomarker, it reflects the average plasma glucose over the previous 8–12 weeks [ 9 ].…”

“…As a biomarker, it reflects the average plasma glucose over the previous 8–12 weeks [ 9 ]. It is currently used for both the diagnosis and management of diabetes [ 8 ] and is recommended as a gold standard in the assessment of diabetes-related outcomes [ 9 , 10 ]. Historically, the elevated level of HbA1c in diabetic patients was reported first by Rahbar and associates in 1968, and over the next decades it became arguably the most important indicator of blood glucose control.…”