Reference Range

Potassium is an electrolyte, which is a mineral in the blood that can be measured by a blood test. Potassium is ingested through food and electrolyte-enhanced beverages and excreted primarily through urine, with a minority portion removed through the gastrointestinal tract.

The reference ranges for blood potassium levels are as follows^[1]:

Adult/elderly: 3.5-5.0 mEq/L or 3.5-5.0 mmol/L (SI units)
Child: 3.4-4.7 mEq/L
Infant: 4.1-5.3 mEq/L
Newborn: 3.9-5.9 mEq/L

Results can be affected by diet, infusion of potassium-containing fluids, or an infusion of glucose or insulin.

Possible critical values are as follows^[1]:

Adult: < 2.5 or >6.5 mEq/L
Newborn: < 2.5 or >8 mEq/L

Interpretation

Conditions associated with high potassium values include the following:

Hyperkalemia
Blood transfusion
Hemolytic anemia (red cell destruction)
Acute kidney injury
Addison's disease
Hypoaldosteronism
Pseudohypoaldosteronism
Tissue injury
Eating disorders (anorexia, bulimia)
Infection
Diabetic ketoacidosis
Dehydration
Excessive potassium intake (dietary or intravenous)
Medications: RAAS inhibitors, NSAIDS, B-blockers, Calcineurin inhibitors, Heparin

Hyperkalemia is defined as a serum potassium concentration greater than the upper limit of the normal range. The range in children and infants is age-dependent, whereas the range for adults is approximately 3.5-5.5 mEq/L. The upper limit may be considerably high in young or premature infants, as high as 6.5 mEq/L.^[2]Because hyperkalemia can cause lethal cardiac arrhythmias, it is one of the most serious electrolyte disturbances.

When the etiology of hyperkalemia remains unclear, calculation of the transtubular potassium gradient (TTKG) using the following formula may be useful:

TTKG = (K+ urine × Osm plasma)/(K+ plasma × Osm urine)

The normal TTKG varies from 5-15. In the setting of hyperkalemia with normal renal excretion of potassium, the TTKG should be greater than 10. A TTKG of less than 8 in the setting of hyperkalemia implies inadequate potassium excretion, which usually results from aldosterone deficiency or unresponsiveness. Checking the serum aldosterone level may be helpful.

With severe dehydration, potassium levels may be elevated (eg, congenital adrenal hyperplasia, acute kidney injury) or low (eg, pyloric stenosis, alkalosis).

Conditions associated with low potassium values include the following:

Hypokalemia
Dehydration
Use of diuretics
Vomiting
Diarrhea
Hyperaldosteronism
Deficient potassium intake
Acetaminophen overdose
Magnesium deficiency

A spot urine potassium measurement is the easiest and most commonly obtained test for hypokalemia. A low urine potassium level (< 20 mEq/L) suggests poor intake, a shift into the intracellular space, or gastrointestinal loss. A clinician should question the patient regarding (1) diarrhea symptoms and use of laxatives; (2) diet and total parenteral nutrition contents; and (3) the use of insulin, excessive bicarbonate supplements, and a history of episodic weakness.

A high urine potassium level (>40 mEq/L) suggests kidney loss. Be sure to examine the patient's medication list and question the patient regarding the use of diuretics.

Look at the acid-base balance; alkalosis suggests vomiting, Bartter syndrome, Gitelman syndrome, diuretic abuse, or mineralocorticoid excess. Acidosis suggests renal tubular acidosis types I or II, or Fanconi syndrome (as is observed with paraproteinemias, amphotericin use, gentamicin use, or glue sniffing [toluene abuse]).

Also measure the magnesium level; if low, correct it before attempting to correct the potassium level. A deficiency of magnesium results in the continual opening of the ROMK channel, allowing potassium to flow out of the tubular cells into the urine unchecked.

Measure the patient's blood pressure. An elevated blood pressure suggests primary hyperaldosteronism, Cushing syndrome, congenital adrenal hyperplasia, glucocorticoid-remediable hypertension, renal artery stenosis, or Liddle syndrome. Low blood pressure suggests diuretic abuse or a renal tubular disorder such as Bartter syndrome, Gitelman syndrome, or renal tubular acidosis.

If the urine potassium level is greater than 20 mEq/L but less than 40 mEq/L, calculate the TTKG. A value less than 3 suggests that the kidney is not wasting excessive potassium, while a value greater than 7 suggests a significant renal loss. This test cannot be applied when the urine osmolality is less than the serum osmolality.

The TTKG is most helpful in discerning whether a low value in a patient with hyperkalemia is due to low aldosterone levels or aldosterone resistance.

Historically, the utility of the TTKG has been investigated in patients with medication-induced hyperkalemia, eg, combination of medications that potentiate hyperkalemia, such as ACE inhibitors, with spironolactone and potassium supplementations; and cyclosporine in kidney transplant patients. It has also been used to guide spironolactone therapy in patients with cirrhosis and ascites.

While more cumbersome to obtain, a 24-hour urine measurement of potassium excretion yields more precise data on exactly how much potassium is being lost through kidney excretion. Because the kidneys are able to conserve potassium up to approximately 10-15 mEq/d, a value of less than 20 mEq/24-hour urine specimen suggests appropriate kidney conservation of potassium, while values above that indicate some degree of kidney wasting. To ensure that a full and accurate 24-hour urine sample has been collected, urine creatinine should be measured simultaneously.

A spot urine sodium and osmolality test obtained simultaneously with a spot urine potassium test can help refine the interpretation of the urine potassium level. A low urine sodium level (< 20 mEq/L) with a high urine potassium level suggests the presence of secondary hyperaldosteronism. If the urine osmolality is high (>700 mOsm/kg), then the absolute value of the urine potassium concentration can be misleading and can suggest that the kidneys are wasting potassium.

Testing for potassium levels may be performed for the following additional conditions:

Acute adrenal crisis
Acute bilateral urinary tract obstruction
Acute nephritic syndrome
Bulimia
Chronic kidney disease
Cushing syndrome
Diabetic ketoacidosis
Primary thrombocythemia
Rhabdomyolysis
Thyrotoxic periodic paralysis

Collection and Panels

Specimen: Blood

Container: Vacuum tube or microtainer

Collection method: Routine venipuncture

Potassium is typically part of the following panels:

Electrolyte panel
Basic metabolic panel
Complete metabolic panel
Used with chloride, sodium, bicarbonate, aldosterone, and renin tests

Description

The normal level of potassium has a narrow range, as it is critical to the function of nerve and muscle cells, most importantly those in the heart. If the level is higher or lower than normal, the risk of an irregular heartbeat increases. Potassium levels are closely related to sodium levels as almost all of the body's sodium is outside the cell, while potassium remains intracellular. Only 2% of the body's potassium is located outside the cells in the blood; this 2% is what is measured in the potassium test. If serum sodium levels go down, serum potassium levels go up. Potassium levels are also affected by the hormone aldosterone, which is produced by the adrenal glands.

Indications/Applications

Potassium blood tests are important in the diagnosis and treatment of patients with hypertension, acute kidney injury, cardiac distress, disorientation, dehydration, nausea, or diarrhea. Some causes of increased potassium values include glomerular disease, adrenocortical insufficiency, diabetic ketoacidosis, sepsis, and spurious in vitro hemolysis. Potential causes of decreased potassium values include renal tubular disease, hyperaldosteronism, treatment of diabetic ketoacidosis, hyperinsulinism, metabolic alkalosis, and diuretic therapy.

Indications for potassium testing include the following:

Routine physical examination
Weakness or cardiac arrhythmia
Checking levels in patients being treated with diuretics or on dialysis
Checking if treatment for potassium levels is effective
Checking patients with hypertension who have kidney or adrenal gland problems
Checking effects of total parenteral nutrition on potassium levels
Checking if cancer treatment is resulting in cell lysis
Monitoring acute hyperkalemia or hypokalemia

Considerations

The physician should ask the patient about any medications being ingested. Certain drugs such as corticosteroids, beta-adrenergic agonists (eg, isoproterenol), alpha-adrenergic antagonists (eg, clonidine), antibiotics (eg, gentamicin, carbenicillin), and the antifungal agent amphotericin B can lead to losses of potassium. Low urine potassium levels may result from the use of glucocorticoids or nonsteroidal anti-inflammatory drugs.