1Complete Laboratory Conversion Nomogram
| Analyte | Conversion Factor | Normal (Conventional) | Normal (SI Units) | Clinical Notes |
|---|
2Why Laboratory Units Differ Globally
The United States, most of South Asia (including India), and parts of Latin America adhere to conventional mass-concentration units—primarily mg/dL (milligrams per decilitre) and g/dL. In contrast, the United Kingdom, Europe, Canada, Australia, and the World Health Organization mandate Système International (SI) molar units—principally mmol/L and µmol/L.
This divergence produces frequent clinical friction when clinicians interpret overseas clinical trials, international clinical guidelines, and imported diagnostic hardware. For instance, the diagnostic fasting plasma glucose cut-off for diabetes is 126 mg/dL in the USA and India, which is exactly equivalent to 7.0 mmol/L in UK NICE guidelines.
3Key Clinical Conversion Pairs to Memorise
- Glucose (Factor 18): Divide mg/dL by 18 to obtain mmol/L. Fasting normal: 70–100 mg/dL (3.9–5.6 mmol/L). Diabetes threshold: ≥126 mg/dL (≥7.0 mmol/L). Critical hypoglycemia: <70 mg/dL (<3.9 mmol/L).
- Creatinine (Factor 88.4): 1 mg/dL ≈ 88.4 µmol/L. Normal adult male: 0.7–1.2 mg/dL (62–106 µmol/L).
- Total Cholesterol (Factor 38.67): Divide mg/dL by 38.67 for mmol/L. Desirable: <200 mg/dL (<5.17 mmol/L). Target LDL in high ASCVD risk: ≤70 mg/dL (≤1.81 mmol/L).
- Triglycerides (Factor 88.57): Divide mg/dL by 88.57 for mmol/L. Hypertriglyceridemia: ≥150 mg/dL (≥1.70 mmol/L). Severe pancreatitis risk threshold: ≥500 mg/dL (≥5.65 mmol/L).
- Total Bilirubin (Factor 17.1): Multiply mg/dL by 17.1 for µmol/L. Clinical scleral icterus typically manifests when bilirubin exceeds 2.5–3.0 mg/dL (43–51 µmol/L).
- Uric Acid (Factor 59.48): Divide mg/dL by 59.48 for mmol/L (or multiply by 59.48 for µmol/L). Treat-to-target chronic gout threshold: <6.0 mg/dL (<357 µmol/L).
4Frequently Asked Questions
Why are different units used for the same laboratory test?+
Units reflect geographic conventions. The SI system uses molar quantities (mmol/L, µmol/L), which count the actual number of molecules. The conventional system uses mass concentrations (mg/dL). Both are accurate; conversion relies on the molecular weight of the substance.
What is the difference between BUN and serum urea?+
BUN (Blood Urea Nitrogen) measures only the nitrogen component of urea (MW 28), while serum urea measures the whole urea molecule (MW 60). In India and the USA, BUN is reported in mg/dL. In the UK, serum urea is reported in mmol/L. Conversion: Urea (mmol/L) = BUN (mg/dL) × 0.357; or BUN (mg/dL) = Urea (mmol/L) × 2.8.
What are common dangerous conversion errors in clinical practice?+
The most critical hazard is misreading blood glucose units (factor of 18): mistaking 18 mmol/L (severe hyperglycemia) for 18 mg/dL (lethal hypoglycemia) causes fatal insulin misadministration. Other common errors include confusing BUN with whole urea (factor of 2.8) and confusing ng/mL with ng/dL in hormonal assays (factor of 100).
Clinical Disclaimer: Reference intervals presented are representative textbook population ranges. Biological reference intervals vary across individual clinical laboratories, analyzer platforms, reagent lots, patient age, biological sex, and gestational status. Always cross-check results against your specific institution's printed laboratory report.