High potassium (hyperkalemia)

Short answer

Hyperkalemia is a rise in serum potassium above the normal range; the NIH gives the normal range as about 3.6–5.0 mmol/L. ^[6] It is rare in healthy kidneys and is often associated with kidney disease or medications. When severe, it can be life-threatening by disturbing heart rhythm; however, whether a high result is real is also a matter of debate, because sample errors are common. This page is for information, not for diagnosis and treatment; assessment belongs to the physician.

At what potassium level does hyperkalemia begin?

There is no single universally accepted definition. The NIH calls serum potassium above 5.0 mmol/L hyperkalemia. ^[6] The UK Kidney Association guideline adopts the threshold of above 5.5 mmol/L set by the European Resuscitation Council (ERC) in 2005 and retained since, and classifies severity as mild (5.5–5.9), moderate (6.0–6.4) and severe (6.5 and above). ^[1] The KDIGO conference summary also states that the common definition is ≥5.5 mmol/L but that there is no shared, standard classification for the mild-moderate-severe distinction, and that serum potassium is generally higher than plasma potassium, so levels vary with the sample analyzed. ^[2]

Frequency varies with the definition. According to the KDIGO summary, the frequency of hyperkalemia defined as ≥5 mmol/L in the general population has been reported at around 1.5%; with a threshold of ≥6 mmol/L, 0.3% was found in a Swiss emergency department. ^[2] The UK Kidney Association guideline reports that, in the Chronic Kidney Disease Prognosis Consortium study, the frequency of hyperkalemia defined as >5.5 mmol/L was 0.49% in the general population and 4.2% in people with chronic kidney disease, and that in-hospital mortality was higher in patients with hyperkalemia (18.1%) than in patients with hypokalemia (5.0%) or normokalemia (3.9%). ^[1]

Is the high result real? Pseudohyperkalemia

A high potassium result does not always show a true excess in the body. According to Smellie’s BMJ article, pseudohyperkalemia (spurious hyperkalemia) is common in blood samples taken in primary care and mostly results from problems with sampling conditions, storage and transport; it is a cause of unnecessary emergency referral and hospital admission. ^[4] As an example, the author describes a patient who was urgently referred to hospital at 21:00 because of a result of 7.2 mmol/L but whose repeat measurement in the emergency department was 4.8 mmol/L; samples from the same practice were being transported in a metal box in cold of down to minus 3 °C in winter, and this practice’s mean potassium values were 0.5 mmol/L higher than the laboratory mean. After a switch to an insulated box, the difference fell to 0.1 mmol/L. ^[4]

Causes of pseudohyperkalemia include difficult venipuncture, fist clenching or prolonged tourniquet use, hemolysis of the sample (in vitro breakdown of red cells), release of potassium by the sample during clotting, thrombocytosis and marked leukocytosis. The KDIGO summary likewise lists a tourniquet left on for more than one minute, fist clenching, centrifugation and clotting, and high white cell or platelet counts. Smellie states that a normal bicarbonate level supports pseudohyperkalemia, because true hyperkalemia is usually accompanied by metabolic acidosis; he adds that in unclear cases an ECG should be considered if potassium is above 6.0 mmol/L. ^{[2] [4]}

The KDIGO summary recommends confirming the first finding in the central laboratory or with another measurement, and states that point-of-care devices performing whole-blood analysis cannot detect hemolysis, so artificial hyperkalemia can be missed. ^[2] This is not a matter on which a person can decide alone that “my result is wrong” or “is right”; repeat measurement and interpretation together with kidney function and symptoms belong to the physician.

What causes hyperkalemia?

The review by Viera and Wouk reports that hyperkalemia is commonly caused by kidney disease, hyperglycemia and medication use, and that potassium disorders can arise from changes in intake, impaired excretion or shifts between the inside and outside of cells. ^[5] The KDIGO summary lists the conditions predisposing to hyperkalemia in emergency departments as moderate-to-severe kidney disease, heart failure, diabetes and marked tissue damage; among medications, it mentions renin-angiotensin-aldosterone system inhibitors (ACE inhibitors, ARBs), potassium-sparing diuretics, nonsteroidal anti-inflammatory drugs (NSAIDs), succinylcholine and digitalis (digoxin). ^[2]

The NIH states that in people with impaired urinary potassium excretion (chronic kidney disease, use of ACE inhibitors or potassium-sparing diuretics), hyperkalemia can develop even if potassium intake is below the AI; and that it can also be seen in type 1 diabetes, congestive heart failure, adrenal insufficiency and liver disease. It also reports that ACE inhibitors and ARBs, and potassium-sparing diuretics such as amiloride and spironolactone, reduce urinary potassium excretion, and that monitoring potassium status is recommended in those who use them. ^[6]

Foods, supplements and salt substitutes

In healthy people with normal kidney function, high dietary potassium intake carries no health risk; the kidneys excrete the excess. A very high amount of potassium supplement or potassium-containing salt substitutes, however, can exceed the kidney’s capacity to excrete and cause acute hyperkalemia even in a healthy person. ^[6] For use of potassium-enriched salt substitute, in the SSaSS trial (China, 20,995 people with a history of stroke or hypertension aged over 60), serious adverse events attributed to hyperkalemia did not increase significantly compared with regular salt (RR 1.04; 95% CI 0.80–1.37). ^[7] However, this finding represents that study group; the NIH and the Turkish Ministry of Health state that people with kidney disorders or those using certain medications should consult a physician before using products that replace salt. ^[8]

Detailed guidePotassium guide: functions, reference intakes and supplement safety→

What are the symptoms?

According to the NIH, hyperkalemia can be symptomless; in severe cases, muscle weakness, paralysis, palpitations, paresthesia (burning or tingling in the extremities) and life-threatening heart rhythm disorders can occur. ^[6] These symptoms are not specific; they appear in many other conditions as well, and the absence of symptoms does not show that hyperkalemia is absent.

Why is the ECG important and how reliable is it?

The KDIGO summary states that in hyperkalemia the toxic effects on the heart’s conduction system can be life-threatening and that the ECG is the basic tool of management. Tall, peaked T waves can be early ECG findings; more severe QRS widening and merging with the ST-T segment lead to a sine-wave appearance. On the other hand, the ECG is normal in up to half of people with hyperkalemia, and this also applies to those with extreme levels of hyperkalemia; in a study of 90 patients, the ECG was reported to be insensitive in detecting hyperkalemia, with no relationship found between T wave changes and serum potassium. A normal ECG is therefore not considered reassuring if potassium has been confirmed to be truly high. ^[2]

The KDIGO Controversies Conference recommended cardiac monitoring and a 12-lead ECG when potassium is above 6.0 mmol/L. In a retrospective study of 188 patients, the ECG findings associated with adverse outcomes were QRS prolongation, symptomatic bradycardia and junctional rhythms. ^[2]

In which situations is urgent assessment needed?

According to Viera and Wouk, the situations requiring urgent treatment are severe or symptomatic potassium disorders, abrupt changes in potassium level, ECG changes and the presence of certain accompanying diseases. ^[5] The severe hyperkalemia symptoms listed by the NIH (marked muscle weakness, paralysis, palpitations) require urgent medical assessment. ^[6] For an unexpectedly high result in a person without symptoms, the sources put confirmation first (repeat measurement, review of kidney function and sample conditions); ^{[4] [2]} however, if the reported value is markedly high or the person has kidney disease or uses a medication that raises potassium, this assessment needs to be done without delay. The UK Kidney Association guideline states that severe hyperkalemia (>6.5 mmol/L) carries a risk of arrhythmia and cardiac arrest and requires rapid diagnosis and intervention; in the same source, in-hospital mortality above 30% was reported in severe cases. ^[1]

How is it treated in hospital?

Treatment is in the hands of the physician. In summary: Viera and Wouk report that in hyperkalemia with ECG changes, calcium is given intravenously to protect the cardiac conduction system, that insulin (together with glucose) and albuterol (salbutamol) are mostly preferred to lower potassium in the acute setting, and that sodium polystyrene sulfonate is reserved for subacute treatment. ^[5] The KDIGO summary states that calcium salts and agents that shift potassium into cells (insulin-glucose, β-agonists) are the basis of acute management, but that only dialysis, potassium binders and loop diuretics remove potassium from the body, and that potassium needs to be checked frequently because of the risk of a rebound rise. ^[2] This page does not give the dose or administration schedule of any drug.

Is dietary adjustment needed?

This topic is individual. The KDIGO summary states that in people with moderate-to-severe kidney disease in whom the hyperkalemia problem persists, dietary guidance should be given on low-potassium foods and avoidance of potassium-rich foods. ^[2] The results of the KDIGO Controversies Conference, on the other hand, state that, as evidence grows on the relationship between plant-based eating and better outcomes, a shift is proposed from dietary restriction toward supporting eating patterns associated with better outcomes, but that there are few data that dietary change returns abnormal serum potassium to normal. ^[3] Neither giving up fruit and vegetables on one’s own nor taking a potassium supplement is therefore supported as a general rule; the plan is made according to kidney function, medications and blood level.

Detailed guideLow potassium (hypokalemia) symptoms and the magnesium connection→ Detailed guideWhich foods contain potassium? Serving table and the DASH pattern→

Main guide: What is potassium? This guide does not recommend a personal dose.