Comparison of the in-feed glucose test and the oral sugar test.
Authors: Smith S, Harris P A, Menzies-Gow N J
Journal: Equine veterinary journal
Summary
# Comparison of the In-Feed Glucose Test and Oral Sugar Test Two practical field tests for assessing insulin sensitivity—the in-feed oral glucose test (OGT) and the oral sugar test (OST)—have gained traction amongst equine practitioners, yet their relative reliability had never been formally established until this crossover study comparing responses in 13 animals (8 ponies and 5 horses) using standardised fasting protocols and serial blood sampling over 180 minutes. Peak insulin concentrations were substantially higher following OGT administration (mean 154 µiu/ml) compared with OST (72 µiu/ml), with insulin reaching peak levels significantly later during OGT (136 minutes versus 63 minutes), and the overall insulin exposure (area under the curve) more than doubling with the glucose-based test. When applying published diagnostic thresholds for insulin dysregulation, the OGT classified 7 of 13 animals as insulin resistant whilst the OST identified only 5, though the tests showed broad agreement in 85% of cases, suggesting meaningful differences exist in their diagnostic utility. Notably, ponies and horses demonstrated different temporal responses between tests, indicating that species differences may influence test interpretation. These findings highlight that whilst OGT and OST are reasonably concordant for clinical decision-making, the tests are not directly interchangeable and practitioners should remain cautious about switching between protocols; further investigation is needed to determine which test more accurately reflects true insulin dysregulation and which might be more appropriate for screening versus definitive diagnosis.
Read the full abstract on PubMed
Practical Takeaways
- •OGT and OST cannot be used interchangeably for assessing insulin sensitivity in the field; choose one protocol and use it consistently for individual horse monitoring
- •OST produces lower and faster insulin responses than OGT, so different reference thresholds for insulin dysregulation apply to each test
- •When using either test, be aware that 15% of horses/ponies may be misclassified depending on which test is chosen; consider clinical context and repeat testing if borderline results
Key Findings
- •OGT produced significantly higher maximal insulin concentrations (154 ± 116 μiu/ml) compared to OST (72 ± 55 μiu/ml, P<0.05)
- •OGT showed longer time to peak insulin (136 ± 52 min) versus OST (63 ± 25 min, P<0.05)
- •OGT and OST showed 85% agreement in identifying insulin dysregulation but disagreed on 2 of 13 animals
- •Results are not directly comparable between the two tests despite both being advocated as field tests of insulin sensitivity