Overview
The oral glucose tolerance test measures plasma glucose before and at protocol-defined times after a standardized oral glucose load to assess carbohydrate tolerance.
Classification
| Element | SOP focus | If violated |
|---|---|---|
| Fasting baseline | Verified preparation | Reschedule/document |
| Glucose load | Correct dose/complete intake | Usually invalidate |
| Timed draws | Exact intervals | Cancel/repeat per SOP |
| Interpretation | Institutional criteria | Verify currently |
Morphologic Features
Conceptual chemistry reference, morphologic cell identification is hematology, not carbohydrate laboratory diagnosis.
Laboratory Characteristics
- Protocol-driven multi-specimen test
- Clock documentation required
- Series integrity before criteria application
Reference Intervals
Diagnostic glucose/A1c cutoffs and reference intervals are method- and institution-specific. Verify current ADA/institutional criteria and method-specific reference intervals, do not treat textbook examples as universal dogma.
| Concept | Meaning | Notes |
|---|---|---|
| Institutional criteria | Local ADA/guideline adoption | Verify currently |
| Plasma vs whole blood | Different matrices | Not automatically interchangeable |
| Method claims | Analyzer/package insert limits | SOP first |
Clinical and Laboratory Significance
OGTT is a guideline pathway for diabetes and gestational diabetes evaluation when protocol is valid, verify current institutional criteria.
Differential Considerations
Mistimed series artifact vs true impaired glucose tolerance; stress/illness effects vs chronic diabetes.
Comparison Tables
Valid vs mistimed OGTT
| Feature | Valid OGTT | Mistimed series |
|---|---|---|
| Interpretability | May apply diagnostic frameworks | Do not force-fit criteria |
| Action | Report with times | Cancel/repeat per SOP |
| Patient impact | Appropriate classification | Risk of misclassification |
Classification Frameworks
ADA/WHO diabetes classification frameworks use laboratory criteria, always verify current institutional adoption; do not invent absolute universal cutoffs as dogma.
Laboratory Notes
- Never invent absolute universal OGTT cutoffs as dogma
- Verify current ADA/institutional criteria and method-specific reference intervals
References
Authoritative textbooks, guidelines, and reviews supporting this reference entry. Verify reference intervals, critical limits, and reflex criteria against institutional protocols and current guideline editions.
Textbooks
- Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 8th ed. Elsevier; 2022.
- McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2021.
- Bishop ML, Fody EP, Schoeff LE. Clinical Chemistry: Principles, Techniques, and Correlations. 9th ed. Jones & Bartlett; 2022.
CLSI and Professional Guidelines
- American Diabetes Association. Standards of Care in Diabetes. Diabetes Care (annual update).
- Clinical and Laboratory Standards Institute. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Standard. CLSI document EP28-A3c. CLSI; 2010.
Frequently Asked Questions
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What is the Oral Glucose Tolerance Test . Chemistry laboratory reference?
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