The electrolyte exclusion effect is the exclusion of electrolytes from the fraction of the total

blood plasma Blood plasma is a light amber-colored liquid component of blood in which blood cells are absent, but contains proteins and other constituents of whole blood in suspension. It makes up about 55% of the body's total blood volume. It is the ...

volume that is occupied by solids. This phenomenon plays an important role in

pseudohyponatremia Isotonic hyponatremia is a form of hyponatremia with mOsm measured between 280 and 295. It can be associated with pseudohyponatremia, or with isotonic infusion of glucose or mannitol. Pseudohyponatremia Certain conditions, such as extraordinar ...

, 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 residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...

and

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids incl ...

) 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, esp ...

), water portion of plasma is replaced with either lipid or protein causing falsely low electrolyte value (

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