Electrolyte exclusion effect

Last updated March 29, 2019

The electrolyte exclusion effect is the exclusion of electrolytes from the fraction of the total blood plasma volume that is occupied by solids.^[1] 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.

An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water. The dissolved electrolyte separates into cations and anions, which disperse uniformly through the solvent. Electrically, such a solution is neutral. If an electric potential is applied to such a solution, the cations of the solution are drawn to the electrode that has an abundance of electrons, while the anions are drawn to the electrode that has a deficit of electrons. The movement of anions and cations in opposite directions within the solution amounts to a current. This includes most soluble salts, acids, and bases. Some gases, such as hydrogen chloride, under conditions of high temperature or low pressure can also function as electrolytes. Electrolyte solutions can also result from the dissolution of some biological and synthetic polymers, termed "polyelectrolytes", which contain charged functional groups. A substance that dissociates into ions in solution acquires the capacity to conduct electricity. Sodium, potassium, chloride, calcium, magnesium, and phosphate are examples of electrolytes.

Blood plasma is a yellowish liquid component of blood that normally holds the blood cells in whole blood in suspension. In other words, it is the liquid part of the blood that carries cells and proteins throughout the body. It makes up about 55% of the body's total blood volume. It is the intravascular fluid part of extracellular fluid (all body fluid outside cells). It is mostly water (up to 95% by volume), and contains dissolved proteins (6–8%) (e.g. serum albumins, globulins, and fibrinogen), glucose, clotting factors, electrolytes (Na⁺, Ca²⁺, Mg²⁺, HCO₃⁻, Cl⁻, etc.), hormones, carbon dioxide (plasma being the main medium for excretory product transportation) and oxygen. It plays a vital role in an intravascular osmotic effect that keeps electrolyte concentration balanced and protects the body from infection and other blood disorders.

The volume of total solids (primarily protein and lipid) 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.^[1]

Protein biological molecule consisting of chains of amino acid residues

Proteins are large biomolecules, or macromolecules, consisting of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells and organisms, and transporting molecules from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes, and which usually results in protein folding into a specific three-dimensional structure that determines its activity.

In biology and biochemistry, a lipid is a biomolecule that is soluble in nonpolar solvents. Non-polar solvents are typically hydrocarbons used to dissolve other naturally occurring hydrocarbon lipid molecules that do not dissolve in water, including fatty acids, waxes, sterols, fat-soluble vitamins, monoglycerides, diglycerides, triglycerides, and phospholipids.

Sodium ions (Na⁺) are necessary in small amounts for some types of plants, but sodium as a nutrient is more generally needed in larger amounts by animals, due to their use of it for generation of nerve impulses and for maintenance of electrolyte balance and fluid balance. In animals, sodium ions are necessary for the aforementioned functions and for heart activity and certain metabolic functions. The health effects of salt reflect what happens when the body has too much or too little sodium. Characteristic concentrations of sodium in model organisms are: 10mM in E. coli, 30mM in budding yeast, 10mM in mammalian cell and 100mM in blood plasma.

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 and in patients with high plasma protein concentration (usually due to paraproteinemia), water portion of plasma is replaced with either lipid or protein causing falsely low electrolyte value (pseudohyponatremia).^[2] 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).^[3]

Hypertriglyceridemia denotes high (hyper-) blood levels (-emia) of triglycerides, the most abundant fatty molecule in most organisms. Elevated levels of triglycerides are associated with atherosclerosis, even in the absence of hypercholesterolemia, and predispose to cardiovascular disease. Very high triglyceride levels also increase the risk of acute pancreatitis. Hypertriglyceridemia itself is usually symptomless, although high levels may be associated with skin lesions known as xanthomas.

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High-density lipoprotein (HDL) is one of the five major groups of lipoproteins. Lipoproteins are complex particles composed of multiple proteins which transport all fat molecules (lipids) around the body within the water outside cells. They are typically composed of 80-100 proteins per particle and transporting up to hundreds of fat molecules per particle.

Low-density lipoprotein one of the five major groups of lipoprotein

Low-density lipoprotein (LDL) is one of the five major groups of lipoprotein which transport all fat molecules around the body in the extracellular water. These groups, from least dense, compared to surrounding water to most dense, are chylomicrons, very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low-density lipoprotein and high-density lipoprotein (HDL). LDL delivers fat molecules to the cells and can drive the progression of atherosclerosis if they become oxidized within the walls of arteries.

Hyponatremia is a low sodium concentration in the blood. It is generally defined as a sodium concentration of less than 135 mmol/L, with severe hyponatremia being below 120 mEq/L. Symptoms can be absent, mild or severe. Mild symptoms include a decreased ability to think, headaches, nausea, and poor balance. Severe symptoms include confusion, seizures, and coma.

Reference ranges for blood tests are sets of values used by a health professional to interpret a set of medical test results from blood samples.

In physiology, body water is the water content of an animal body that is contained in the tissues, the blood, the bones and elsewhere. The percentages of body water contained in various fluid compartments add up to total body water (TBW). This water makes up a significant fraction of the human body, both by weight and by volume. Ensuring the right amount of body water is part of fluid balance, an aspect of homeostasis.

$Serum (blood) cell free fraction of blood$

In blood, the serum is the component that is neither a blood cell, nor a clotting factor; it is the blood plasma not including the fibrinogens. Serum includes all proteins not used in blood clotting and all the electrolytes, antibodies, antigens, hormones, and any exogenous substances.

Hypernatremia, also spelled hypernatraemia, is a high concentration of sodium in the blood. Early symptoms may include a strong feeling of thirst, weakness, nausea, and loss of appetite. Severe symptoms include confusion, muscle twitching, and bleeding in or around the brain. Normal serum sodium levels are 135 – 145 mmol/L. Hypernatremia is generally defined as a serum sodium level of more than 145 mmol/L. Severe symptoms typically only occur when levels are above 160 mmol/L.

In pharmacology, the volume of distribution is the theoretical volume that would be necessary to contain the total amount of an administered drug at the same concentration that it is observed in the blood plasma. It is defined as the distribution of a medication between plasma and the rest of the body after oral or parenteral dosing.

Fluid balance is an aspect of the homeostasis of organisms in which the amount of water in the organism needs to be controlled, via osmoregulation and behavior, such that the concentrations of electrolytes in the various body fluids are kept within healthy ranges. The core principle of fluid balance is that the amount of water lost from the body must equal the amount of water taken in; for example, in humans, the output must equal the input. Euvolemia is the state of normal body fluid volume, including blood volume, interstitial fluid volume, and intracellular fluid volume; hypovolemia and hypervolemia are imbalances. Water is necessary for all life on Earth. Humans can survive for 4 to 6 weeks without food but only for a few days without water.

The anion gap is a value calculated from the results of multiple individual medical lab tests. It may be reported with the results of an electrolyte panel, which is often performed as part of a comprehensive metabolic panel.

Osmotic concentration, formerly known as osmolarity, is the measure of solute concentration, defined as the number of osmoles (Osm) of solute per litre (L) of solution. The osmolarity of a solution is usually expressed as Osm/L, in the same way that the molarity of a solution is expressed as "M". Whereas molarity measures the number of moles of solute per unit volume of solution, osmolarity measures the number of osmoles of solute particles per unit volume of solution. This value allows the measurement of the osmotic pressure of a solution and the determination of how the solvent will diffuse across a semipermeable membrane (osmosis) separating two solutions of different osmotic concentration.

Fresh frozen plasma (FFP) is a blood product made from the liquid portion of whole blood. It is used to treat conditions in which there are low blood clotting factors (INR>1.5) or low levels of other blood proteins. It may also be used as the replacement fluid in plasma exchange. Using ABO compatible plasma, while not required, may be recommended. Use as a volume expander is not recommended. It is given by slow injection into a vein.

Distribution in pharmacology is a branch of pharmacokinetics which describes the reversible transfer of a drug from one location to another within the body.

In medicine, the BUN-to-creatinine ratio is the ratio of two serum laboratory values, the blood urea nitrogen (BUN) (mg/dL) and serum creatinine (Cr) (mg/dL). Outside the United States, particularly in Canada and Europe, the truncated term urea is used and the units are different (mmol/L). The units of creatinine are also different (μmol/L), and this value is termed the urea-to-creatinine ratio. The ratio may be used to determine the cause of acute kidney injury or dehydration.

Lercanidipine is an antihypertensive drug. It belongs to the dihydropyridine class of calcium channel blockers, which work by relaxing and opening the blood vessels allowing the blood to circulate more freely around the body. This lowers the blood pressure and allows the heart to work more efficiently.

The fractional excretion of sodium (FE_Na) is the percentage of the sodium filtered by the kidney which is excreted in the urine. It is measured in terms of plasma and urine sodium, rather than by the interpretation of urinary sodium concentration alone, as urinary sodium concentrations can vary with water reabsorption. Therefore, the urinary and plasma concentrations of sodium must be compared to get an accurate picture of renal clearance. In clinical use, the fractional excretion of sodium can be calculated as part of the evaluation of acute kidney failure in order to determine if hypovolemia or decreased effective circulating plasma volume is a contributor to the kidney failure.

Lipoprotein lipase deficiency is a genetic disorder in which a person has a defective gene for lipoprotein lipase, which leads to very high triglycerides, which in turn causes stomach pain and deposits of fat under the skin, and which can lead to problems with the pancreas and liver, which in turn can lead to diabetes. The disorder only occurs if a child acquires the defective gene from both parents. It is managed by restricting fat in diet to less than 20 g/day.

Blood plasma fractionation refers to the general processes of separating the various components of blood plasma, which in turn is a component of blood obtained through blood fractionation.

Conductivity of an electrolyte solution is a measure of its ability to conduct electricity. The SI unit of conductivity is Siemens per meter (S/m).

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.

References

1 2 Burtis CA, Ashwood ER, Bruns DE (2012). Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier Health Sciences. ISBN 978-1-4160-6164-9.
↑ Bangert SK, Marshall WJ (2008). Clinical Biochemistry: Metabolic and Clinical Aspects (2nd ed.). Edinburgh: Churchill Livingstone/Elsevier. ISBN 978-0-443-10186-1.
↑ Goldwasser, P.; Ayoub, I.; Barth, R. (2015). Pseudohypernatremia and Pseudohyponatremia: A linear correction. Nephrology Dialysis Transplantation 30:252-257.

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[Tietz_textbook-1] 1 2 Burtis CA, Ashwood ER, Bruns DE (2012). Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier Health Sciences. ISBN 978-1-4160-6164-9.

[Clinical_biochemistry-2] Bangert SK, Marshall WJ (2008). Clinical Biochemistry: Metabolic and Clinical Aspects (2nd ed.). Edinburgh: Churchill Livingstone/Elsevier. ISBN 978-0-443-10186-1.

[NDT-3] Goldwasser, P.; Ayoub, I.; Barth, R. (2015). Pseudohypernatremia and Pseudohyponatremia: A linear correction. Nephrology Dialysis Transplantation 30:252-257.