Makindo Medical Notes

Related Subjects: |Type 1 DM |Type 2 DM |Diabetes in Pregnancy |HbA1c |Diabetic Ketoacidosis (DKA) Adults |Hyperglycaemic Hyperosmolar State (HHS) |Diabetic Nephropathy |Diabetic Retinopathy |Diabetic Neuropathy

🧪 HbA1c reflects average blood glucose control over ~3 months (lifespan of an erythrocyte 🩸). It provides a long-term marker of glycaemic control compared to daily glucose fluctuations.

ℹ️ About

• 📊 HbA1c reflects integrated blood glucose control over 120 days.
• 🍬 Formed by glucose binding covalently to haemoglobin (HbA beta chain valine).
• 🔄 Sensitive to changes in glycaemic control in the 4 weeks before measurement.
• 📏 Reported in mmol/mol (IFCC). Conversion:
  IFCC HbA1c (mmol/mol) = [DCCT HbA1c(%) − 2.15] × 10.929
• ↗️ Rough guide: +11 mmol/mol ≈ +2 mmol/L (36 mg/dL) in mean blood glucose.

🧬 Aetiology

• ⚡ Glycosylation = glucose binds terminal valine of HbA beta chain.
• 📈 Proportional to mean glucose exposure over ~6 weeks.
• 🔹 Fructosamine = glycosylated albumin → reflects control over 2–3 weeks (shorter window).

🎯 Uses

• 🧑‍⚕️ Guides long-term diabetes management (Type 1 & Type 2).
• 📉 On average, oral hypoglycaemic drugs ↓ HbA1c by ~1%.
• 💊 HbA1c >8% ➝ usually needs pharmacotherapy (not just diet).
  HbA1c >9% ➝ consider insulin.
• 👩‍🍼 In pregnancy ➝ Fructosamine is preferred (shorter half-life, avoids misleading HbA1c).
• ⚠️ Falsely low in haemoglobinopathies (e.g., thalassaemia, sickle cell).

📖 Interpretation

• ✅ Normal population: ~4.5–6.5% (25–48 mmol/mol).
• 🎯 Target in diabetes: 6.5–7.0% (realistically 7.0% for many patients).
• 🏥 Clinical Trials:
  • DCCT (Type 1 DM): showed HbA1c links to microvascular complications.
  • UKPDS (Type 2 DM): confirmed HbA1c as a marker of microangiopathy risk.
• 📐 Standardisation: IFCC/DCCT alignment avoids inter-lab errors.