Decreased Levels of HbA1c Caused by a Low Threshold of Urine Glucose Excretion in Two Cases with Impaired Glucose Tolerance

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  • Ono Yosuke
    Department of Internal Medicine, Japan Self Defense Forces Central Hospital
  • Nobuhara Keiko
    Department of Internal Medicine, Japan Self Defense Forces Central Hospital
  • Hinata Takashi
    Department of Internal Medicine, Japan Self Defense Forces Central Hospital
  • Kodera Tsutomu
    Department of Internal Medicine, Japan Self Defense Forces Central Hospital
  • Takahashi Yukihiro
    Department of Internal Medicine, Japan Self Defense Forces Central Hospital
  • Ito Toshimitsu
    Department of Internal Medicine, Japan Self Defense Forces Central Hospital
  • Yasuda Hiroko
    Wakagi Clinic

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Other Title
  • 尿糖排泄閾値低下によるHbA1c値の低下が示唆された境界型糖尿病の2症例
  • 症例報告 尿糖排泄閾値低下によるHbA1c値の低下が示唆された境界型糖尿病の2症例
  • ショウレイ ホウコク ニョウ トウ ハイセツ シキイチ テイカ ニ ヨル HbA1cチ ノ テイカ ガ シサ サレタ キョウカイガタ トウニョウビョウ ノ 2 ショウレイ

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Two patients with impaired glucose tolerance at our clinic exhibited a high urine glucose concentration despite a normal HbA1c level (5.4-5.5 %). We performed 75-g oral glucose tolerance tests (OGTTs) to assess the pathophysiological mechanisms in the two cases (Cases 1 and 2). We also performed 75g-OGTTs in two randomly selected cases as a control group (Cases 3 and 4). One of the two control subjects was a healthy person with a normal HbA1c level, while the other had borderline diabetes mellitus. In the two cases (Cases 1 and 2), blood glucose curves showed the borderline type. The patients also exhibited a low response in the early phase of insulin secretion. The insulinogenic index was 0.18-0.25. Additional secretion in the two cases reactively increased, with a peak at 120 minutes. The urine glucose concentrations were remarkably increased compared with those observed in the serum at 60 minutes and 120 minutes after glucose intake. We infer from the results that the renal glucose threshold was low in the two borderline patients compared with that observed in the two control subjects who demonstrated normal glycosuria. These results shed new light on the threshold for renal glycosuria, which differs from that outlined in the former definition of renal glycosuria. High urine glucose excretion hindering the glycation of serum blood may lower the HbA1c level. The HbA1c level is an essential tool for diagnosing diabetes mellitus, and the urine glucose level may become another criterion for the diagnosis of diabetes mellitus.

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