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Cited by 32Diabetes Management and ResearchPancreatic function and diabetesDiabetes, Cardiovascular Risks, and Lipoproteins

Carbohydrate Intake Prior to Oral Glucose Tolerance Testing

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Klein, Klara R, Walker, Christopher P, McFerren, Amber L, Huffman, Halie, Frohlich, Flavio, Buse, John B·2021·Journal of the Endocrine Society
DOI 10.1210/jendso/bvab049PMC PMC8059359
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Abstract

With the emergence of glycated hemoglobin as a diagnostic test for diabetes, oral glucose tolerance tests (OGTTs) have become rare in endocrinology practice. As they have moved out of favor, the importance of patient instructions on preparation prior to OGTT has faded from memory. Decades-old literature, well-known to endocrinologists a generation ago, emphasized the importance of carbohydrate intake prior to OGTT. In this expert endocrine consult, we discuss an OGTT performed in a research setting without adequate carbohydrate intake at the evening meal prior to the OGTT. The resultant elevated plasma glucose levels at 1-hour and 2-hours mimicked the loss of first-phase insulin release seen in early type 1 and type 2 diabetes. With clinical concern that the research participant had evolving type 1 or type 2 diabetes, the volunteer was subjected to additional testing and experienced anxiety. Repeat OGTT was normal after adequate carbohydrate intake (>150 grams/day and >50 grams the evening prior to overnight fast for the study). The physiology of this phenomenon is explored and is likely mediated through beta cell adaptation and alteration in peripheral glucose uptake in response to nutrient exposure. The learnings of decades ago have clearly faded, and this literature should be revisited to ensure that OGTT results are not compromised when ordered for clinical or research purposes.

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  • Fasting and carbohydrate restriction can falsely elevate glucose level with an oral glucose challenge.

    “Fasting and carbohydrate restriction can falsely elevate glucose level with an oral glucose challenge.”

    From 2. Diagnosis and Classification of Diabetes: <i>Standards of Care in Diabetes—2024</i> (2024) · cites this paper as [12]

    The Case Report describes a false-positive oral glucose tolerance test after a low-carbohydrate dinner, and the Conclusion warns that inadequate carbohydrate preparation can cause false-positive results. The paper does not say that fasting itself falsely elevates glucose during the test; its Conclusion recommends a 10–16-hour overnight fast as part of proper preparation. (LLM, conf=0.90)

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  • Antecedent carbohydrate restriction in the days prior to OGTT can falsely elevate postchallenge glucose levels, potentially resulting in a false-positive OGTT.

    “Antecedent carbohydrate restriction in the days prior to OGTT can falsely elevate postchallenge glucose levels, potentially resulting in a false-positive OGTT (12).”

    From 2. Diagnosis and classification of diabetes: standards of care in diabetes-2025 (2025) · cites this paper as [12]

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Authors
Klein, K. R., Walker, C. P., McFerren, A. L., Huffman, H., Frohlich, F., & Buse, J. B.
Affiliations
  • University of North Carolina at Chapel Hill (US)
  • Department of Psychiatry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
Corresponding author
Klein, Klara R
ORCID
Venue
Journal of the Endocrine Society
Publisher
The Endocrine Society
Published
2021-03-29
Volume
5
Issue
5
Pages
bvab049-bvab049
ISSN
2472-1972 (ISSN-L)
DOI
10.1210/jendso/bvab049
PMC
PMC8059359
OpenAlex
W3149880023
Cited by
32
References
5
Citations by year
2026: 4 · 2025: 4 · 2024: 7 · 2023: 7 · 2022: 8 · 2021: 2
FWCI
4.48
Type
journal article
Language
en
Open access
Licence
Locations
  • Journal of the Endocrine Society (publishedVersion, cc-by-nc-nd)
  • PubMed Central (publishedVersion, cc-by-nc-nd)
  • PubMed (publishedVersion)
Funders
  • Nutrition Obesity Research Center (P30DK56350)
  • North Carolina Translational and Clinical Sciences Institute (UL1TR002489)
  • North Carolina Diabetes Research Center (P30DK124723)
Topics
  • Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Diabetes Management and Research
  • Health Sciences › Medicine › Surgery › Pancreatic function and diabetes
  • Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Diabetes, Cardiovascular Risks, and Lipoproteins
Keywords
oral glucose tolerance test, carbohydrate intake, exam preparation, first-phase insulin secretion, beta-cell adaptation, peripheral glucose uptake, type 1 diabetes, type 2 diabetes, HbA1c, plasma glucose

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