Can dehydration cause high A1C?


Editorial team Published on

Yes, dehydration can cause a temporary spike in blood glucose concentration, but it does not significantly change your true long-term A1C levels.

How Dehydration Affects Blood Sugar

  • Concentrated blood volume: When you are dehydrated, you have less water in your body, which decreases your blood volume. This makes the glucose already in your bloodstream more concentrated, causing a higher reading on a standard blood sugar test.
  • Stress hormones: Dehydration triggers stress hormones like vasopressin (arginine vasopressin), cortisol, and epinephrine. These hormones tell your liver to release more glucose and can increase insulin resistance, raising your blood sugar further.
  • The diabetes cycle: High blood sugar causes frequent urination, which leads to dehydration. Dehydration then concentrates blood sugar further, creating a difficult cycle to manage.

Does It Impact an A1C Test?

  • A1C measures a 3-month average: Your A1C test measures the percentage of glycated hemoglobin (hemoglobin coated with sugar) over the past two to three months.
  • No long-term change: Drinking or not drinking water on the day of your blood draw might cause minor fluctuations in immediate blood glucose or plasma volume, but standard modern laboratory tests (using HPLC assays) are not falsely elevated by acute dehydration.
  • The reverse link: If chronic poor hydration habits contribute to ongoing, poorly managed blood sugar spikes over months, that sustained high glucose will eventually raise your A1C.