Diabetes-related investigations
How to read HbA1c (and when it lies), glucose tests including the 1-hour OGTT, fructosamine and CGM metrics, C-peptide and islet antibodies for classifying diabetes, urine albumin-to-creatinine ratio, and the acid-base workup of DKA and HHS, with worked examples.
Tier 1Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- HbA1c reflects glucose over about 8 to 12 weeks, weighted to the last month. Diabetes is 48 mmol/mol (6.5%) or more; it fails whenever red cell lifespan changes.
- Glucose thresholds (fasting 7.0, 2-hour OGTT 11.1, random 11.1 with symptoms) are in Type 2 diabetes. The IDF now also proposes a 1-hour OGTT value.
- C-peptide measures endogenous insulin secretion. With islet antibodies it classifies diabetes when the phenotype is unclear.
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Sources
- Standards of Care in Diabetes 2026: Section 2, Diagnosis and classification of diabetesAmerican Diabetes Association (Diabetes Care 2026;49(Suppl 1)), 2026 (January 2026 full update)
- Management of type 2 diabetes, a handbook for general practiceAU/NZRoyal Australian College of General Practitioners and Diabetes Australia, Recommendations last revised August 2025
- Australian Evidence-Based Clinical Guidelines for Diabetes (living guidelines)AU/NZLiving Evidence for Diabetes Consortium (Australian Diabetes Society, Diabetes Australia and partners), Living guideline on MAGICapp, checked November 2026
- International Diabetes Federation position statement on the 1-hour post-load plasma glucose for the diagnosis of intermediate hyperglycaemia and type 2 diabetesBergman M et al., Diabetes Res Clin Pract 2024;209:111589, 2024
- Hag Elagib MA, Ahmed RA, Eltom H et al. Iron deficiency, iron deficiency anemia, and HbA1c levels in nondiabetic adults: a systematic review and meta-analysis. Cureus 2026;18(8):e115191Cureus, 2026
- Management of type 1 diabetes in adults. A consensus report by the ADA and EASDHolt RIG et al., Diabetologia 2021;64:2609-52, 2021
- KDIGO 2024 clinical practice guideline for the evaluation and management of chronic kidney diseaseKidney Disease Improving Global Outcomes (Kidney Int 2024;105(4S):S117-S314), 2024
- Chronic kidney disease (CKD) management in primary careAU/NZKidney Health Australia, 5th edition, 2024
- Last updated
- 14 November 2026
What changed
- 14 November 2026 Turnstile bot check on sign-in and signed-out feedback