The HbA1c-Adjusted Slow Valley Height Ratio, a Depth Indicator of the Valley Between HbA1c and HbA0 Measured by High-Performance Liquid Chromatography, Is Useful for the Diagnosis of Hb Toranomon.

Objective: HbA1c values in patients with Hb Toranomon, a hemoglobin variant, are falsely high when measured with the Tosoh high-performance liquid chromatography (HPLC) analyzer. Moreover, a phenomenon has been observed in which the valley between HbA1c and HbA0 [slow valley (SV)] appears shallow on the chromatograms measured by the Tosoh HPLC analyzer in patients with Hb Toranomon. In the present study, the usefulness of the indicator, HbA1c (A1c)-adjusted SV height rate (AaSVHR), as a screening test for Hb Toranomon to quantify the SV height (SVH) was investigated.

Methods: This study included six patients with Hb Toranomon and 100 control participants, comprising 50 diabetic patients and 50 non-diabetic participants. The SVH between HbA1c and HbA0 and the height of HbA1c (A1cH) on HPLC (G9) chromatograms were measured to determine the ratio of SVH to A1cH [SVH ratio (SVHR)]. Given that the SVHR obtained showed a significant negative correlation with HbA1c measured by HPLC, SVHR was corrected with HbA1c [A1c-adjusted SVHR (AaSVHR)], but it showed no significant correlation with HbA1c.

Results: AaSVHR exceeded 14% across all participants with Hb Toranomon, but it was no more than 14% in all control participants.

Conclusions: AaSVHR measurements are useful as an Hb Toranomon screening test in patients whose HbA1c measured with a Tosoh HPLC analyzer is falsely high. A high AaSVHR exceeding 14% raises a strong suspicion for the presence of a hemoglobin variant including Hb Toranomon.