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Potassium – K+
Reference interval K+ – examples
Distribution and physiological significance of potassium
Why measure potassium ?
Physiological control of extracellular fluid potassium concentration
Causes of hypokalemia
Symptoms of hypokalemia
Causes of hyperkalemia
Symptoms of hyperkalemia
Potassium (K+) is the major cation in the intracellular fluid, where it has a 25 – 37-fold higher concentration (∼150 mmol/L in tissue cells, ∼105 mmol/L in erythrocytes) than in the extracellular fluid (∼4 mmol/L) [4, 106]. K+ has several vital functions in the body, e.g. regulation of neuromuscular excitability, regulation of heart rhythm, regulation of intracellular and extracellular volume and acid-base status.
Reference interval K+ – examples
Serum samples return values slightly [3 – 5 %] higher than plasma samples .
Distribution and physiological significance of potassium
The human body contains around 3500 mmol (137 g) K+, nearly all (98 %) of which is contained within cells; only 1.5 % is contained in the extracellular fluid at an approximate concentration of 4.0 mmol/L (Fig. 13). Intracellular K+ concentration, by contrast, is close to 150 mmol/L . The intracellular-to-extracellular ratio (150/4 ) results in an electric potential gradient across the cellular membrane and plays a major role in establishing the resting cell membrane potential, particularly in cardiac and neuromuscular cells . Even small changes in the extracellular K+ concentration will have significant effects on the transmembrane potential gradient, and thereby the function of neuromuscular and cardiac tissues . This large concentration gradient across cellular membranes is maintained by the Na+/K+-ATPase pump, located in the cellular membrane .
This is an energy-consuming process of continuous ”pumping” of two K+ into cells in exchange for three Na+ . The K+ concentration gradient is a determinant of the resting membrane potential and thereby the electrical properties of ”excitable” cells, including their ability to transmit electrical signals.
Why measure potassium?
Disturbance of potassium handling and consequent abnormality in K+ is a potential feature of a number of acute and chronic illnesses, some of which are relatively common. It is also a potential adverse effect of some commonly prescribed drugs . An estimated 20 – 30 % of hospitalized patients have abnormal K+ . Diagnosing of K+ disturbance is important because if it remains untreated, it can cause significant morbidity and in the most severe cases, sudden cardiac arrest . All this accounts for K+ being one of the most frequently requested/measured parameters of blood chemistry.
Physiological control of extracellular fluid potassium concentration
Extracellular fluid K+ concentration (cK+) represents the balance between K+ intake and K+ loss. A typical western diet ensures a K+ intake of around 40 – 200 mmol/day . Although a small amount (∼5 mmol/day) is normally excreted via the gastrointestinal tract, the major route of excretion is urine, and K+ balance depends largely on mechanisms that ensure renal regulation of K+ loss in urine so that it matches K+ intake . Renal regulation of K+ excretion depends on the adrenal hormone aldosterone; rising cK+ stimulates its synthesis and release . Aldosterone thus reduces cK+ by increasing renal excretion of K+.
Internal redistribution of K+, i.e. the movement of K+ into and out of cells, is an additional factor that can affect cK+ without affecting whole body potassium . Insulin stimulates the Na+/K+-ATPase pump and thereby the movement of K+ into cells; insulin thus has the effect of reducing cK+. Reciprocal movement of K+ and hydrogen ions (H+) across cellular membranes determines that cK+ is affected by acid-base status (Fig. 9). Due to this high intracellular concentration of K+, any pathology associated with marked cell destruction (lysis) results in massive efflux of K+ from cells, and consequent increase in cK+.
Maintaining potassium within reference intervals depends on:
- Adequate dietary intake of K+
- Normal renal function
- Normal gastrointestinal tract function
- Normal production of aldosterone by adrenal glands
- Maintenance of normal acid-base balance
- Normal action of the Na+/K+-ATPase pump and integrity of cell membranes
Disturbance of any of the above can cause abnormality in K+.
Reduced cK+ (i.e. <3.5 mmol/L) is called hypokalemia .
Increased cK+ (i.e. >5.0 mmol/L) is called hyperkalemia .
Of the two conditions, hypokalemia is the more common, affecting a broader range of patients, while hyperkalemia is potentially more serious and occurs almost exclusively in patients with some underlying renal abnormalities [112, 117].
Causes of hypokalemia
- Diuretic therapy – most common cause . Confined to so-called ”K+-wasting diuretics” (thiazides and loop diuretics) that can cause inappropriate loss of K+ in urine
- Severe or chronic diarrhea/vomiting (increased loss of K+ via the gastrointestinal tract)
- Metabolic alkalosis (movement of K+ into cells)
- Conn’s syndrome/disease (increased aldosterone levels)
- Treatment of diabetic ketoacidosis (due to increased loss of K+ in urine)
- Inadequate K+ intake (starvation)
- Laxative abuse (increased loss of K+ via the gastrointestinal tract)
- Liquorice abuse (liquorice contains a substance that causes effective increased aldosterone levels) 
- Beta blocker drug therapy (K+ moves into cells)
- Insulin overdose (K+ moves into cells) 
Symptoms of hypokalemia
Mild hypokalemia, i.e. cK+ in the range of 3.0 – 3.5 mmol/L, is usually asymptomatic
Symptoms of moderate decrease cK+ include :
- Fatigue associated with muscular weakness
- Constipation due to impaired muscle tone of the gastrointestinal tract
- Characteristic ECG changes
Severe hypokalemia (cK+ <2.5 mmol/L) may also cause:
- Flaccid paralysis
- Respiratory failure (if the respiratory musculature is affected) 
- Cardiac arrhythmias (including potentially fatal ventricular arrhythmia)
- Cardiac arrest
Causes of hyperkalemia [110, 116, 119]
- Chronic kidney disease – most common cause (reduced urinary excretion of K+)
- Metabolic acidosis, including diabetic ketoacidosis (movement of K+ out of cells)
- Severe tissue damage, e.g. rhabdomyolysis, trauma, major surgery (K+ derived from damaged cells)
- Cytotoxic drug therapy for hematological malignancy (K+ derived from drug-damaged cells)
- Addison’s disease (reduced aldosterone levels)
- Excessive K+ replacement therapy
- Some drugs (ACE inhibitors, spironolactone and other so-called ”K+-sparing diuretics”)
Symptoms of hyperkalemia
Symptoms may be absent or relatively non-specific, emphasizing the clinical importance of measuring cK+ among those at risk; when they do occur, symptoms include [110, 116, 121]:
- Muscle weakness/fatigue
- Diarrhea/abdominal pain
- Cardiac palpitations
- Characteristic ECG changes
The risk of potentially fatal ventricular arrhythmia and cardiac arrest increases as cK+ rises above 6.5 mmol/L [110, 121].
Both severe hypokalemia  and severe hyperkalemia  are medical emergencies requiring prompt intervention.
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- Malin GL et al. Strength of association between umbilical cord pH and perinatal and long term outcomes: systematic review and meta-analysis. BMJ 2010; 340:c1471.
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Effective Date January 20th, 2023 (last updated January 20th, 2023)
ABOUT THIS POLICYRadiometer values your privacy and the protection of your personal data. This policy (“Policy”) explains how Radiometer its affiliates, subsidiaries or related companies, a full list of which can be located here (together, “Radiometer”, “our”, “us”, or “we”), collects, uses, shares, transfers and processes data collected from or about you.
“Personal Data” is any information that can be used to directly or indirectly identify an individual or that can be reasonably expected to link to an individual. This can include items such as name, address, telephone number, credit card details, email address, ID number, Internet Protocol (“IP”) address of an electronic device used by an individual, or other identifying code (even absent of other identifying information). Statistical and non-identifiable metric data are not considered Personal Data.
The Radiometer subsidiary, affiliate or related company with which you interact is, where applicable, the data controller (or equivalent under applicable law) responsible for the processing of your Personal Data. You can find a list of the relevant legal entities that act as data controllers in Appendix 1 to this Policy.
SCOPEThis Policy describes the types of Personal Data that we may collect, process or disclose about you and how you may govern this processing by exercising applicable legal rights. This Policy applies to both online and offline information collection, including your use of websites or subdomains operated by us, any mobile applications, when we provide products and/or services to you or notify you about prospective items of interest and in other situations where you interact with us in-person, by telephone or by mail where this Policy is posted or referenced.
There may be occasion where you have been provided with a circumstance-specific privacy notice that is separate from this policy, such as privacy notices for specific activities such as Recruitment. To the extent you were provided with a different notice, those notices apply and govern our interactions with you. If you provide Personal Data about parties other than yourself, you are responsible for ensuring their knowledge of how we will process their personal data, and, where applicable, obtaining any necessary consents required in advance.
We are committed to processing Personal Data in accordance with applicable laws. Please note that if you do not wish to provide your Personal Data to us, some products and/or services may become unavailable to you. Your use of any or all these platforms indicates you have been notified of our collection, use, transfer, and disclosure of your information as described in this Policy to the extent permitted by applicable law.Read more