Blood vs Plasma [Glucose].TXT

Created : 2011-10-17
Revised : 2011-10-17
Author : Tom Coleman
Copyright : 2011-2011
By : University of Mississippi Medical Center

The issue here is that home glucose monitors
(usually) report blood glucose contentration
while clinical labs report plasma or serum
glucose concentration.

A comprehensive model should consider both
measures.

UNITS ======================================

Both mG/dL and mMol/L are the physical units
used for [glucose].


CONVERSIONS ================================

The molecular weight of glucose is 180
(C6-H12-O6), so

Multiply mMol/L by 18 to get mG/dL

Multiply mG/dL by 1/18 (0.0555) to get mMol/L

Multiply [Blood Glucose] by 1.15 to get
[Plasma/Serum Glucose]. More on this below.

NORMAL VALUES ==============================

 [Glucose] ~ 100 mG/dL
           ~ 5.5 mMol/L

without distinguishing between blood and
plasma.

DERIVATION =================================

Erythrocytes or red blood cells (RBC's)
metabolise glucose anaerobically (this is,
down to pyruvate).

The RBC's cell membrane is permeable to glucose
and this permeability is not modulated by
insulin.

Thus, the assumption (and maybe there is some
data) is that [Glucose] in the cytosol is equal
to [Glucose] in the plasma.

The confounding factor is that RBC's contain a
lot of solid (hemoglobin, hgb) and this is what
makes blood and plasma glucose concentrations
differ.

HumMod uses this fraction, although I do not
have the reference in hand.

  RBC's Solids = 0.34 * Total Volume

Consider 1 mL of blood, hct of 44, [glucose]
of 1 mG/mL blood, glucose mass of 1 mG.

  Plasma = 0.56 mL
  RBC's = 0.44 mL
    RBC's H2O = 0.29 mL
    RBC's Solids = 0.15 mL
  Total H2O = 0.85 mL
  [Plasma Glucose] = 1.18

This is where the 1.15 multiplier comes from.

Maybe some good data on [Glucose] and
[Insulin] over 24 hours with 3 meals per day.

Daly, Mark E. Acute effects on insulin
sensitivity and diurnal metabolic profiles of
a high-sucrose compared with a high starch
diet. Am. J. Clin. Nutr. 67:1186–1196, 1998.

	
End
