Does a person with a fasting blood glucose (FBG) level of 180 mg/dL and a Hemoglobin A1c (HbA1c) of 5.7% have diabetes?

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Last updated: May 15, 2025 • View editorial policy

Differential Diagnosis for Elevated Fasting Blood Glucose and HbA1c

Given a fasting blood glucose of 180 and an HbA1c of 5.7, the diagnosis of diabetes is not straightforward. Here's a differential diagnosis organized into categories:

  • Single Most Likely Diagnosis + Impaired Fasting Glucose (IFG): The fasting glucose level is elevated, but the HbA1c is below the diagnostic threshold for diabetes (6.5%). This suggests that the person may have impaired fasting glucose, a prediabetic state.
  • Other Likely Diagnoses + Stress-Induced Hyperglycemia: The elevated fasting glucose could be a response to stress, which can raise blood glucose levels. This is a common occurrence in hospitalized patients or those under significant psychological stress. + Recent Illness or Infection: Certain illnesses or infections can cause temporary elevations in blood glucose levels, even in non-diabetic individuals.
  • Do Not Miss Diagnoses + Diabetes Mellitus: Although the HbA1c is below the diagnostic threshold, it's essential to consider the possibility of diabetes, especially if the patient has symptoms or risk factors. A repeat HbA1c test or an oral glucose tolerance test (OGTT) may be necessary to confirm the diagnosis. + Cushing's Syndrome: This rare endocrine disorder can cause hyperglycemia due to excess cortisol production. Although unlikely, it's a critical diagnosis to consider due to its potential severity. + Pheochromocytoma: This rare tumor can cause episodic hyperglycemia due to excess catecholamine production. Although rare, it's a potentially life-threatening condition that should not be missed.
  • Rare Diagnoses + Glucagonoma: A rare pancreatic tumor that produces excess glucagon, leading to hyperglycemia. + Somatostatinoma: A rare pancreatic tumor that produces excess somatostatin, leading to hyperglycemia. + Hormonal Imbalance: Certain hormonal imbalances, such as hyperthyroidism or acromegaly, can cause hyperglycemia.

It's essential to note that a comprehensive evaluation, including a thorough medical history, physical examination, and additional laboratory tests, is necessary to determine the underlying cause of the elevated fasting blood glucose and HbA1c.

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.