Ionic Composition of Body Fluids:

The following table gives representative values for the primary ionic constituents of the major fluid compartments. Also, follow the links at left for additional important information.

Electrolyte	Plasma, (mEq/L) [molarity]	Plasma Water (mEq/L) [molality]	Interstitial Fluid (mEq/L)	Intracellular Fluid (mEq/L)
Cations:
Sodium	142	153	145	10
Potassium	4	4.3	4	160
Calcium	5	5.4	5	2
Magnesium	2	2.2	2	26
Total Cations:	153	165	156	198

Anions:
Chloride	101	108.5	114	3
Bicarbonate	27	29	31	10
Phosphate	2	2.2	2	100
Sulphate	1	1	1	20
Organic Acid	6	6.5	7
Protein	16	17	1	65
Total Anions:	153	165	156	198

Important Notes:

The units of measure given in the table are in equivalents, referred to either liter volume or liter water (plasma). If you are not familiar with the terms molarity, molality, osmolarity, osmolality, equivalents, and tonicity, please review Units of Measure.

Plasma has approximately 7% (by volume) proteins and lipids. However, the ionic activity is limited to the aqueous portion of the solution. Labs report concentrations as mEq/Liter Plasma. You must correct for the 7% non-aqueous portion to obtain the actual concentrations (if needed). This is why the numbers in the second plasma column are higher than the first.

Not all of the reported concentrations are FREE. Some ions are bound to proteins or other ions.

Proteins have many negative charges per molecule. The equivalents given above are therefore much higher than the molarity of those same proteins.

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Copyright 1999, Joe Patlak, Department of Physiology, University of Vermont.
For comments, problems or questions regarding this web contact Joe Patlak.
Last updated: November 01, 2000.