What are the 5 key electrolytes?

What are electrolytes?

Chemically, electrolytes are substances that become ions in solution and acquire the capacity to conduct electricity. Electrolytes are present in the human body, and the balance of the electrolytes in our bodies is essential for normal function of our cells and our organs.

Common electrolytes that are measured by doctors with blood testing include sodium, potassium, chloride, and bicarbonate. The functions and normal range values for these electrolytes are described below.

Sodium

Sodium is the major positive ion (cation) in fluid outside of cells. The chemical notation for sodium is Na+. When combined with chloride, the resulting substance is table salt. Excess sodium (such as that obtained from dietary sources) is excreted in the urine. Sodium regulates the total amount of water in the body and the transmission of sodium into and out of individual cells also plays a role in critical body functions. Many processes in the body, especially in the brain, nervous system, and muscles, require electrical signals for communication. The movement of sodium is critical in the generation of these electrical signals. Therefore, too much or too little sodium can cause cells to malfunction, and extremes in the blood sodium levels (too much or too little) can be fatal.

• Increased sodium (hypernatremia) in the blood occurs whenever there is excess sodium in relation to water. There are numerous causes of hypernatremia; these may include kidney disease, too little water intake, and loss of water due to diarrhea and/or vomiting.
• A decreased concentration of sodium (hyponatremia) occurs whenever there is a relative increase in the amount of body water relative to sodium. This happens with some diseases of the liver and kidney, in patients with congestive heart failure, in burn victims, and in numerous other conditions.

A Normal blood sodium level is 135 - 145 milliEquivalents/liter (mEq/L), or in international units, 135 - 145 millimoles/liter (mmol/L).

Potassium

Potassium is the major positive ion (cation) found inside of cells. The chemical notation for potassium is K+. The proper level of potassium is essential for normal cell function. Among the many functions of potassium in the body are regulation of the heartbeat and the function of the muscles. A seriously abnormal increase in potassium (hyperkalemia) or decrease in potassium (hypokalemia) can profoundly affect the nervous system and increases the chance of irregular heartbeats (arrhythmias), which, when extreme, can be fatal.

• Increased potassium is known as hyperkalemia. Potassium is normally excreted by the kidneys, so disorders that decrease the function of the kidneys can result in hyperkalemia. Certain medications may also predispose an individual to hyperkalemia.
• Hypokalemia, or decreased potassium, can arise due to kidney diseases; excessive losses due to heavy sweating, vomiting, diarrhea, eating disorders, certain medications, or other causes.

The normal blood potassium level is 3.5 - 5.0 milliEquivalents/liter (mEq/L), or in international units, 3.5 - 5.0 millimoles/liter (mmol/L).

Chloride

Chloride is the major anion (negatively charged ion) found in the fluid outside of cells and in the blood. An anion is the negatively charged part of certain substances such as table salt (sodium chloride or NaCl) when dissolved in liquid. Chloride plays a role in helping the body maintain a normal balance of fluids.

The balance of chloride ion (Cl-) is closely regulated by the body. Significant increases or decreases in chloride can have deleterious or even fatal consequences:

• Increased chloride (hyperchloremia): Elevations in chloride may be seen in diarrhea, certain kidney diseases, and sometimes in overactivity of the parathyroid glands.
• Decreased chloride (hypochloremia): Chloride is normally lost in the urine, sweat, and stomach secretions. Excessive loss can occur from heavy sweating, vomiting, and adrenal gland and kidney disease.

The normal serum range for chloride is 98 - 108 mmol/L.

Bicarbonate

The bicarbonate ion acts as a buffer to maintain the normal levels of acidity (pH) in blood and other fluids in the body. Bicarbonate levels are measured to monitor the acidity of the blood and body fluids. The acidity is affected by foods or medications that we ingest and the function of the kidneys and lungs. The chemical notation for bicarbonate on most lab reports is HCO3- or represented as the concentration of carbon dioxide (CO2). The normal serum range for bicarbonate is 22-30 mmol/L.

The bicarbonate test is usually performed along with tests for other blood electrolytes. Disruptions in the normal bicarbonate level may be due to diseases that interfere with respiratory function, kidney diseases, metabolic conditions, or other causes.

References

Medically reviewed by Joseph T. Palermo, DO; Board Certified Internal Medicine/Geriatric Medicine REFERENCE: "Maintenance and replacement fluid therapy in adults"

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Electrolytes are essential for basic life functioning, such as maintaining electrical neutrality in cells, generating and conducting action potentials in the nerves and muscles. Sodium, potassium, and chloride are the significant electrolytes along with magnesium, calcium, phosphate, and bicarbonates. Electrolytes come from our food and fluids. 

These electrolytes can have an imbalance, leading to either high or low levels. High or low levels of electrolytes disrupt normal bodily functions and can lead to even life-threatening complications. This article reviews the basic physiology of electrolytes and their abnormalities, and the consequences of electrolyte imbalance.  

Sodium

Sodium, which is an osmotically active cation, is one of the most important electrolytes in the extracellular fluid. It is responsible for maintaining the extracellular fluid volume, and also for regulation of the membrane potential of cells. Sodium is exchanged along with potassium across cell membranes as part of active transport. 

Sodium regulation occurs in the kidneys. The proximal tubule is where the majority of sodium reabsorption takes place. In the distal convoluted tubule, sodium undergoes reabsorption.  Sodium transport takes place via sodium-chloride symporters, which are by the action of the hormone aldosterone.[1]

Among the electrolyte disorders, hyponatremia is the most frequent. Diagnosis is when the serum sodium level is less than 135 mmol/L. Hyponatremia has neurological manifestations. Patients may present with headaches, confusion, nausea, delirium. Hypernatremia presents when the serum sodium levels are greater than145 mmol/L. Symptoms of hypernatremia include tachypnea, sleeping difficulty, and feeling restless. Rapid sodium corrections can have serious consequences like cerebral edema and osmotic demyelination syndrome. 

Potassium

Potassium is mainly an intracellular ion. The sodium-potassium adenosine triphosphatase pump has the primary responsibility for regulating the homeostasis between sodium and potassium, which pumps out sodium in exchange for potassium, which moves into the cells. In the kidneys, the filtration of potassium takes place at the glomerulus. The reabsorption of potassium takes place at the proximal convoluted tubule and thick ascending loop of Henle.[2] Potassium secretion occurs at the distal convoluted tubule. Aldosterone increases potassium secretion.[3] Potassium channels and potassium-chloride cotransporters at the apical membrane also secrete potassium.[2]

Potassium disorders are related to cardiac arrhythmias. Hypokalemia occurs when serum potassium levels under 3.6 mmol/L—weakness, fatigue, and muscle twitching present in hypokalemia. Hyperkalemia occurs when the serum potassium levels are above 5.5 mmol/L, which can result in arrhythmias. Muscle cramps, muscle weakness, rhabdomyolysis, myoglobinuria are presenting signs and symptoms in hyperkalemia.[4]

Calcium

Calcium has a significant physiological role in the body. It is involved in skeletal mineralization, contraction of muscles, the transmission of nerve impulses, blood clotting, and secretion of hormones. The diet is the predominant source of calcium. It is mostly present in the extracellular fluid. Absorption of calcium in the intestine is primarily under the control of the hormonally active form of vitamin D, which is 1,25-dihydroxy vitamin D3. Parathyroid hormone also regulates calcium secretion in the distal tubule of kidneys.[5] Calcitonin acts on bone cells to increase the calcium levels in the blood.

Hypocalcemia diagnosis requires checking the serum albumin level to correct for total calcium, and the diagnosis is when the corrected serum total calcium levels are less than 8.8 mg/dl, as in vitamin D deficiency or hypoparathyroidism. CHecking serum calcium levels is a recommended test in post-thyroidectomy patients.[6] Hypercalcemia is when corrected serum total calcium levels exceed 10.7 mg/dl, as seen with primary hyperparathyroidism. Humoral hypercalcemia presents in malignancy, primarily due to PTHrP secretion.[7] 

Bicarbonate

The acid-base status of the blood drives bicarbonate levels. The kidneys predominantly regulate bicarbonate concentration and are responsible for maintaining the acid-base balance. Kidneys reabsorb the filtered bicarbonate and also generate new bicarbonate by net acid excretion, which occurs by excretion of both titrable acid and ammonia. Diarrhea usually results in loss of bicarbonate, thus causing an imbalance in acid-base regulation.[8] 

Magnesium

Magnesium is an intracellular cation. Magnesium is mainly involved in ATP metabolism, contraction and relaxation of muscles, proper neurological functioning, and neurotransmitter release. When muscle contracts, calcium re-uptake by the calcium-activated ATPase of the sarcoplasmic reticulum is brought about by magnesium.[9] Hypomagnesemia occurs when the serum magnesium levels are less under 1.46 mg/dl. It can present with alcohol use disorder and gastrointestinal and renal losses—ventricular arrhythmias, which include torsades de pointes seen in hypomagnesemia. 

Chloride

Chloride is an anion found predominantly in the extracellular fluid. The kidneys predominantly regulate serum chloride levels. Most of the chloride, which is filtered by the glomerulus, is reabsorbed by both proximal and distal tubules (majorly by proximal tubule) by both active and passive transport.[10] 

Hyperchloremia can occur due to gastrointestinal bicarbonate loss. Hypochloremia presents in gastrointestinal losses like vomiting or excess water gain like congestive heart failure. 

Phosphorus

Phosphorus is an extracellular fluid cation. Eighty-five percent of the total body phosphorus is in the bones and teeth in the form of hydroxyapatite; the soft tissues contain the remaining 15%. Phosphate plays a crucial role in metabolic pathways. It is a component of many metabolic intermediates and, most importantly of adenosine triphosphate(ATPs) and nucleotides. Phosphate is regulated simultaneously with calcium by Vitamin D3, PTH, and calcitonin. The kidneys are the primary avenue of phosphorus excretion. 

Phosphorus imbalance may result due to three processes: dietary intake, gastrointestinal disorders, and excretion by the kidneys.[11]

A blood specimen for electrolytes use lithium heparin tubes, plus the standard phlebotomy equipment and personnel, as with any blood draw.[12]

Blood collected in lithium heparin tubes then goes to the laboratory for evaluation of serum electrolytes.[12]

Indications to order serum electrolyte panel are numerous. Some of which include:

1. As a part of routine blood investigations  

2. For in-patients and ICU patients, the monitoring of serum electrolytes often occurs daily or more frequently as they can be affected by the medications, fluid therapy, diet changes, and illnesses.

3. Any illness that can cause electrolyte derangement- malnutrition, gastrointestinal disorders, cardiac disorders, kidney dysfunction, endocrine disorders, circulatory disorders, lung disorders, acid-base imbalance

4. Arrhythmias, cardiac arrest

5. Use of diuretics or any medications that can interfere with fluid and electrolyte homeostasis

Measurement of electrolytes will help the clinicians in the diagnosis of a medical condition, the effectiveness of treatment, and the potential side effect of medications. Examples include: 

1. A patient with heart failure receiving diuretics needs a workup for potassium, bicarbonate, magnesium as diuretics can exert adverse effects on electrolyte balance.

2. A patient that presents with weakness needs a basic electrolyte workup, as an electrolyte imbalance, especially in sodium and potassium levels, can lead to fatigue

Laboratory Values: 

Serum Sodium: 

Normal Range: 135 to 145 mmol/L  

Mild-moderate Hyponatremia: 125 to 135 mmol/L, Severe: less than 125 mmol/L

Hypernatremia: Mild-moderate: 145 to 160 mmol/L, Severe: over 160 mmol/L

Serum Potassium:

Normal Range: 3.6 to 5.5 mmol/L 

Hypokalemia: Mild Hypokalemia under 3.6 mmol/L, Moderate: 2.5 mmol/L, Severe : greater than 2.5 mmol/L

Hyperkalemia: Mild hyperkalemia: 5 to 5.5 mmol/L, Moderate- 5.5 to 6.5, Severe: 6.5 to 7 mmol/L

Serum Calcium: 

Normal Range: 8.8 to 10.7 mg/dl

Hypercalcemia: greater than 10.7 mg/dl , Severe: over 11.5 mg/dl 

Hypocalcemia: less than 8.8 mg/dl

Serum Magnesium: 

Normal Range: 1.46 to 2.68 mg/dl 

Hypomagnesemia: under 1.46 mg/dl

Hypermagenesemia: over 2.68

Bicarbonate:

Normal Range: 23 to 30 mmol/L

It increases or decreases depending on the acid-base status.

Phosphorus:

Normal Range: 3.4 to 4.5 mg/dl 

Hypophosphatemia: less than 2.5 mg/dl

Hyperphosphatemia: greater than 4.5 mg/dl

Hypomagnesemia can lead to hypocalcemia as it interferes with the action of parathormone. 

Administration of intravenous insulin is associated with a spurious decrease in potassium levels as insulin shifts potassium intracellularly.[13]

Most of the calcium remains bound to proteins, out of which albumin-bound calcium comprises about 80%. Therefore, a patient with hypoalbuminemia, as seen in liver cirrhosis, the nephrotic syndrome will demonstrate low calcium levels vs. the actual values.[14]

Both hyponatremia and hypernatremia, as well as hypomagnesemia, can lead to neurological consequences such as seizure disorders. 

Hypokalemia and hyperkalemia, as well as hypocalcemia, are more responsible for arrhythmias. 

Bicarbonate imbalance can lead to metabolic acidosis or alkalosis.

A piece of valuable advice to the patients would be to take the medications exactly as prescribed by the clinicians to avoid electrolyte imbalance as a consequence of not taking the prescribed dose. 

One should call for immediate medical help when the patient feels weak, has muscle ache, or has altered consciousness.  

Some of the common causes of electrolyte disorders seen in clinical practices are:

• Hyponatremia: low dietary sodium intake, primary polydipsia, SIADH, congestive heart failure, hepatic cirrhosis, failure of adrenal glands, hyperglycemia, dyslipidemia

• Hypernatremia: unreplaced fluid loss through the skin and gastrointestinal tract, osmotic diuresis, hypertonic saline administration

• Hypokalemia: hyperaldosteronism, loop diuretics 

• Hyperkalemia: increase release from cells as in metabolic acidosis, insulin deficiency, beta-blocker or decreased potassium excretion as in acute or chronic kidney disease, aldosterone deficiency or resistance

• Hypercalcemia: malignancy, hyperparathyroidism, chronic granulomatous disease

• Hypocalcemia: acute pancreatitis, parathyroid hormone deficiency after thyroidectomy, neck dissection, resistance to parathormone, hypomagnesemia, sepsis 

• Hypermagnesemia: increase oral magnesium intake

• Hypomagnesemia: renal losses as in diuretics, alcohol use disorder, or GI losses as in diarrhea

• Bicarbonate level: increases in primary metabolic alkalosis or compensation to primary respiratory acidosis - decreases in primary metabolic acidosis or compensation to primary respiratory alkalosis.

• Hyperchloremia: normal saline infusion

• Hypochloremia: GI loss as in diarrhea, renal losses with diuretics

• Hypophosphatemia: refeeding syndrome, vitamin D deficiency, hyperparathyroidism

• Hyperphosphatemia: hypoparathyroidism, chronic kidney disease

Review Questions

1.

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Gumz ML, Rabinowitz L, Wingo CS. An Integrated View of Potassium Homeostasis. N Engl J Med. 2015 Jul 02;373(1):60-72. [PMC free article: PMC5675534] [PubMed: 26132942]

Ellison DH, Terker AS, Gamba G. Potassium and Its Discontents: New Insight, New Treatments. J Am Soc Nephrol. 2016 Apr;27(4):981-9. [PMC free article: PMC4814195] [PubMed: 26510885]

Viera AJ, Wouk N. Potassium Disorders: Hypokalemia and Hyperkalemia. Am Fam Physician. 2015 Sep 15;92(6):487-95. [PubMed: 26371733]

Veldurthy V, Wei R, Oz L, Dhawan P, Jeon YH, Christakos S. Vitamin D, calcium homeostasis and aging. Bone Res. 2016;4:16041. [PMC free article: PMC5068478] [PubMed: 27790378]

Cooper MS, Gittoes NJ. Diagnosis and management of hypocalcaemia. BMJ. 2008 Jun 07;336(7656):1298-302. [PMC free article: PMC2413335] [PubMed: 18535072]

Turner JJO. Hypercalcaemia - presentation and management . Clin Med (Lond). 2017 Jun;17(3):270-273. [PMC free article: PMC6297576] [PubMed: 28572230]

Hamm LL, Nakhoul N, Hering-Smith KS. Acid-Base Homeostasis. Clin J Am Soc Nephrol. 2015 Dec 07;10(12):2232-42. [PMC free article: PMC4670772] [PubMed: 26597304]

Jahnen-Dechent W, Ketteler M. Magnesium basics. Clin Kidney J. 2012 Feb;5(Suppl 1):i3-i14. [PMC free article: PMC4455825] [PubMed: 26069819]

Morrison G. Serum Chloride. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd ed. Butterworths; Boston: 1990. [PubMed: 21250151]

Berkelhammer C, Bear RA. A clinical approach to common electrolyte problems: 3. Hypophosphatemia. Can Med Assoc J. 1984 Jan 01;130(1):17-23. [PMC free article: PMC1875686] [PubMed: 6418367]

Toffaletti J, Ernst P, Hunt P, Abrams B. Dry electrolyte-balanced heparinized syringes evaluated for determining ionized calcium and other electrolytes in whole blood. Clin Chem. 1991 Oct;37(10 Pt 1):1730-3. [PubMed: 1914173]

Liamis G, Liberopoulos E, Barkas F, Elisaf M. Spurious electrolyte disorders: a diagnostic challenge for clinicians. Am J Nephrol. 2013;38(1):50-7. [PubMed: 23817179]

Boden SD, Kaplan FS. Calcium homeostasis. Orthop Clin North Am. 1990 Jan;21(1):31-42. [PubMed: 2404236]