Whole Blood to Plasma Glucose Converter
Whole Blood to Plasma Glucose Converter
Convert whole blood glucose to plasma-equivalent mg/dL, and check whether your meter has already applied this conversion.
Whole Blood → Plasma Glucose
Whole blood ⇄ plasmaWhole blood glucose 100 mg/dL
Formula
- 1.11
- the standard average conversion factor, from the difference in water content between red cells and plasma
- mmol/L
- divide the plasma mg/dL result by 18.016
- caution
- most modern meters and analysers already report a plasma-equivalent value from a whole blood sample — see below before applying this factor
Worked example
Whole blood glucose 100 mg/dL
100 × 1.11 = 111 mg/dL plasma
111 ÷ 18.016 = 6.2 mmol/L
Common whole blood to plasma conversions
| Whole blood (mg/dL) | Plasma-equivalent (mg/dL) | Plasma (mmol/L) |
|---|---|---|
| 70 | 78 | 4.3 |
| 100 | 111 | 6.2 |
| 126 | 140 | 7.8 |
| 200 | 222 | 12.3 |
Why the factor exists, and why most meters have already applied it
Glucose dissolves in the water phase of blood, and red cells contain proportionally less water per unit volume than plasma does. At an identical true glucose concentration, a whole blood sample therefore reads about 11% lower than the plasma from the same sample — the basis of the ×1.11 conversion factor. This is why the diagnostic thresholds that define impaired fasting glucose and diabetes are all defined in plasma terms, historically the matrix used in laboratory chemistry.
The important practical point is that this conversion is, in nearly all cases, something you do not need to do yourself. Modern glucose meters and point-of-care analysers are calibrated internally to report a plasma-equivalent value even though the sample applied to the strip is capillary whole blood — this has been standard practice since the mid-2000s and is required for meters compliant with ISO 15197. A meter reading of 100 mg/dL is already telling you the plasma-equivalent figure, not the raw whole-blood value.
This converter exists for the less common case of a genuinely uncorrected whole blood reading — certain point-of-care blood gas analysers, or older, non-plasma-calibrated devices — or for comparing a whole-blood-based method against plasma-based diagnostic criteria. Applying the ×1.11 factor to an already plasma-calibrated meter reading double-converts the value and inflates it by roughly 11%, so check what your specific device or assay reports before using this calculator.
Frequently asked questions
Why is plasma glucose higher than whole blood glucose?
Red cells hold less water per unit volume than plasma, and glucose dissolves in the water phase, so an identical true concentration reads about 11% lower in whole blood than in plasma.
Do I need to convert my glucose meter reading?
Almost certainly not. Modern meters are calibrated to report a plasma-equivalent value directly from a whole blood sample, so the ×1.11 conversion has usually already been applied for you.
What is the whole blood to plasma conversion factor?
Approximately 1.11 — multiply whole blood glucose in mg/dL by 1.11 to get the plasma-equivalent value, assuming a normal haematocrit.
How do I convert mg/dL to mmol/L?
Divide the mg/dL value by 18.016. A plasma glucose of 111 mg/dL is 6.2 mmol/L.
Related calculators
References
- D’Orazio P et al. Approved IFCC recommendation on reporting results for blood glucose. Clin Chem. 2005;51(9):1573–6.
- ISO 15197:2013. In vitro diagnostic test systems — requirements for blood-glucose monitoring systems for self-testing.