Aims
Hb Toranomon [β112 (G14) Cys → Try] was the variant hemoglobin first reported by Harano et al. (Hemoglobin 20:361–369, 1996). Since 2004 there have been successive reports of Hb Toranomon based on abnormal HbA1c levels measured by high-performance liquid chromatography (HPLC). HbA1c levels are known to vary depending on the HPLC model used. We compared the HbA1c measured by new and old HPLC models in patients with Hb Toranomon.
Method
Eight patients with Hb Toranomon (5 men, 3 women; 4 with diabetes and 4 without diabetes; 7 heterozygotes, 1 homozygote) were studied. HbA1c levels measured using the old HPLC models (Arkray HA-8150 and Tosoh GHb III) and the new HPLC models (Arkray HA-8160 or later, Tosoh GHbV or later) were compared with the results of immunoassay, enzymatic assay, affinity assay of HbA1c, and glycated albumin (GA).
Results
HbA1c levels measured by the old and new Arkray models were 10 and 30% lower, respectively, and those measured by the new Tosoh models were 30% higher than the results of immunoassay. The same trends were found in comparisons with the HbA1c results of enzymatic and affinity assays or GA.
Conclusion
Glycated variant hemoglobins, such as Hb Toranomon, may have previously been measured as HbA1c and are difficult to identify because of the low divergence from other glycemic control indicators in the old HPLC models. The recent detection of successive Hb Toranomon patients is likely due to the abnormally low or high HbA1c levels by the upgraded measuring models.