The electrolyte exclusion effect is the exclusion of

electrolyte An electrolyte is a substance that conducts electricity through the movement of ions, but not through the movement of electrons. This includes most soluble Salt (chemistry), salts, acids, and Base (chemistry), bases, dissolved in a polar solven ...

s from the fraction of the total

blood plasma Blood plasma is a light Amber (color), amber-colored liquid component of blood in which blood cells are absent, but which contains Blood protein, proteins and other constituents of whole blood in Suspension (chemistry), suspension. It makes up ...

volume that is occupied by solids. This phenomenon plays an important role in pseudohyponatremia, an error affecting measurements made by either flame photometry or indirect potentiometry but not by direct potentiometry. The volume of total solids (primarily

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

and

lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

) in a plasma sample is approximately 7%, so that only 93% is water. The main electrolytes are confined to water phase. So for example in 10 μL plasma sample, only 9.3 μL is water that contains the electrolyte. Thus if the concentration of an electrolyte, say Na⁺ is determined to be 140 mmol/L, it is the concentration in total plasma volume, not in plasma water volume. This phenomenon produces only a slight difference as volume fraction of water in plasma is sufficiently constant. But, in patients with severe endogenous or exogenous

hypertriglyceridemia Hypertriglyceridemia is the presence of high amounts of triglycerides in the blood. Triglycerides are the most abundant fatty molecule in most organisms. Hypertriglyceridemia occurs in various physiologic conditions and in various diseases, and ...

and in patients with high plasma protein concentration (usually due to

paraproteinemia Monoclonal gammopathy, also known as paraproteinemia, is the presence of excessive amounts of myeloma protein or monoclonal gamma globulin in the blood. It is usually due to an underlying immunoproliferative disorder or hematologic neoplasms, espe ...

), water portion of plasma is replaced with either lipid or protein causing falsely low electrolyte value ( pseudohyponatremia). Conversely, in patients with low plasma protein concentration (a finding often seen in critical care), the water content of plasma is higher than normal, resulting in the reciprocal artifact, a falsely high electrolyte value (pseudohypernatremia).

References

{{Reflist, refs = {{Cite book , last1=Burtis , first1=Carl A. , title=Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. , last2=Ashwood , first2=Edward R. , last3=Bruns , first3=David E. , publisher=Elsevier Health Sciences , year=2012 , isbn=978-1-4160-6164-9 , name-list-style=vanc {{Cite book , last1=Bangert , first1=Stephen K , title=Clinical Biochemistry: Metabolic and Clinical Aspects , last2=Marshall , first2=William J. , publisher=Churchill Livingstone/Elsevier , year=2008 , isbn=978-0-443-10186-1 , edition=2nd , location=Edinburgh , name-list-style=vanc {{Cite book , last1=Goldwasser , first1=P. , title=Pseudohypernatremia and Pseudohyponatremia: A linear correction , last2=Ayoub , first2=I. , last3=Barth , first3=R. , publisher=Nephrology Dialysis Transplantation 30:252-257 , year=2015 Electrolyte disturbances