Potassium, Blood

(redirected from Serum K+)

Potassium, Blood

Synonym/acronym: Serum K+.

Common use

To evaluate fluid and electrolyte balance related to potassium levels toward diagnosing disorders such as acidosis, renal failure, dehydration, and monitor the effectiveness of therapeutic interventions.


Serum (1 mL) collected in a gold-, red-, or red/gray-top tube. Plasma (1 mL) collected in green-top (heparin) tube is also acceptable.

Normal findings

(Method: Ion-selective electrode)
SerumConventional & SI Units
Cord5.6–12 mEq/L or mmol/L
1–12 hr5.3–7.3 mEq/L or mmol/L
12–24 hr5.3–8.9 mEq/L or mmol/L
24–48 hr5.2–7.3 mEq/L or mmol/L
48–72 hr5–7.7 mEq/L or mmol/L
3–7 days3.2–5.5 mEq/L or mmol/L
8 days–1 mo3.4–6 mEq/L or mmol/L
1–5 mo3.5–5.6 mEq/L or mmol/L
6 mo–1 yr3.5–6.1 mEq/L or mmol/L
2–19 yr3.8–5.1 mEq/L or mmol/L
Adult–older adult3.5–5.3 mEq/L or mmol/L
Note: Serum values are 0.1 mmol/L higher than plasma values, and reference ranges should be adjusted accordingly. It is important that serial measurements be collected using the same type of collection container to reduce variability of results from collection to collection.Older adults are at risk for hyperkalemia due to the decline in aldosterone levels, decline in renal function, and effects of commonly prescribed medications that inhibit the renin-angiotensin-aldosterone system.


Electrolytes dissociate into electrically charged ions when dissolved. Cations, including potassium, carry a positive charge. Body fluids contain approximately equal numbers of anions and cations, although the nature of the ions and their mobility differs between the intracellular and extracellular compartments. Both types of ions affect the electrical and osmolar functions of the body. Electrolyte quantities and the balance among them are controlled by oxygen and carbon dioxide exchange in the lungs; absorption, secretion, and excretion of many substances by the kidneys; and secretion of regulatory hormones by the endocrine glands. Potassium is the most abundant intracellular cation with a number of essential functions to include transmission of electrical impulses in cardiac and skeletal muscle and participation in enzyme reactions that transform glucose into energy and amino acids into proteins. Potassium also helps maintain acid-base equilibrium, and it has a significant and inverse relationship to pH: A decrease in pH of 0.1 increases the potassium level by 0.6 mmol/L.

Abnormal potassium levels can be caused by a number of contributing factors, which can be categorized as follows:

  • Altered renal excretion: Normally, 80% to 90% of the body’s potassium is filtered out through the kidneys each day (the remainder is excreted in sweat and stool); renal disease can result in abnormally high potassium levels.
  • Altered dietary intake: A severe potassium deficiency can be caused by an inadequate intake of dietary potassium.
  • Altered cellular metabolism: Damaged red blood cells (RBCs) release potassium into the circulating fluid, resulting in increased potassium levels.

This procedure is contraindicated for



  • Assess a known or suspected disorder associated with renal disease, glucose metabolism, trauma, or burns
  • Assist in the evaluation of electrolyte imbalances; this test is especially indicated in elderly patients, patients receiving hyperalimentation supplements, patients on hemodialysis, and patients with hypertension
  • Evaluate cardiac arrhythmia to determine whether altered potassium levels are contributing to the problem, especially during digitalis therapy, which leads to ventricular irritability
  • Evaluate the effects of drug therapy, especially diuretics
  • Evaluate the response to treatment for abnormal potassium levels
  • Monitor known or suspected acidosis, because potassium moves from RBCs into the extracellular fluid in acidotic states
  • Routine screen of electrolytes in acute and chronic illness

Potential diagnosis

Increased in

  • Acidosis (intracellular potassium ions are expelled in exchange for hydrogen ions in order to achieve electrical neutrality)
  • Acute renal failure (potassium excretion is diminished, and it accumulates in the blood)
  • Addison’s disease (due to lack of aldosterone, potassium excretion is diminished, and it accumulates in the blood)
  • Asthma (related to chronic inflammation and damage to lung tissue)
  • Burns (related to tissue damage and release by damaged cells)
  • Chronic interstitial nephritis (potassium excretion is diminished, and it accumulates in the blood)
  • Dehydration (related to hemoconcentration)
  • Dialysis (dialysis treatments simulate kidney function, but potassium builds up between treatments)
  • Diet (related to excessive intake of salt substitutes or of potassium salts in medications)
  • Exercise (related to tissue damage and release by damaged cells)
  • Hemolysis (massive) (potassium is the major intracellular cation)
  • Hyperventilation (in response to respiratory alkalosis, blood levels of potassium are increased in order to achieve electrical neutrality)
  • Hypoaldosteronism (due to lack of aldosterone, potassium excretion is diminished, and it accumulates in the blood)
  • Insulin deficiency (insulin deficiency results in movement of potassium from the cell into the extracellular fluid)
  • Ketoacidosis (insulin deficiency results in movement of potassium from the cell into the extracellular fluid)
  • Leukocytosis
  • Muscle necrosis (related to tissue damage and release by damaged cells)
  • Near drowning
  • Pregnancy
  • Prolonged periods of standing
  • Tissue trauma (related to release by damaged cells)
  • Transfusion of old banked blood (aged cells hemolyze and release intracellular potassium)
  • Tubular unresponsiveness to aldosterone
  • Uremia

Decreased in

    Alcoholism (related to insufficient dietary intake) Alkalosis (potassium uptake by cells is increased in response to release of hydrogen ions from cells) Anorexia nervosa (related to significant changes in renal function that result in hypokalemia) Bradycardia (hypokalemia can cause bradycardia) Chronic, excessive licorice ingestion (from licorice root) Licorice inhibits short-chain dehydrogenase/reductase enzymes. These enzymes normally prevent cortisol from binding to aldosterone receptor sites in the kidney. In the absence of these enzymes, cortisol acts on the kidney and triggers the same effects as aldosterone, which include increased potassium excretion, sodium retention, and water retention. Congestive heart failure (related to fluid retention and hemodilution) Crohn’s disease (insufficient intestinal absorption) Cushing’s syndrome (aldosterone facilitates the excretion of potassium by the kidneys) Diet deficient in meat and vegetables (insufficient dietary intake) Excess insulin (insulin causes glucose and potassium to move into cells) Familial periodic paralysis (related to fluid retention) Gastrointestinal (GI) loss due to vomiting, diarrhea, nasogastric suction, or intestinal fistula Hyperaldosteronism (aldosterone facilitates the excretion of potassium by the kidneys) Hypertension (medications used to treat hypertension may result in loss of potassium; hypertension is often related to diabetes and renal disease, which affect cellular retention and renal excretion of potassium, respectively) Hypomagnesemia (magnesium levels tend to parallel potassium levels) IV therapy with inadequate potassium supplementation Laxative abuse (related to medications that cause potassium wasting) Malabsorption (related to insufficient intestinal absorption) Pica (eating substances of no nutritional value, e.g., clay) Renal tubular acidosis (condition results in excessive loss of potassium) Sweating (related to increased loss) Theophylline administration, excessive (theophylline drives potassium into cells, reducing circulating levels) Thyrotoxicosis (related to changes in renal function)

Critical findings

  • Adults & children
  • Less than 2.5 mEq/L or mmol/L (SI: Less than 2.5 mEq/L or mmol/L)
  • Greater than 6.2 mEq/L or mmol/L (SI: Greater than 6.2 mEq/L or mmol/L)
  • Newborns
  • Less than 2.8 mEq/L or mmol/L (SI: Less than 2.8 mmol/L)
  • Greater than 7.6 mEq/L or mmol/L (SI: Greater than 7.6 mmol/L)
  • Consideration may be given to verifying the critical findings before action is taken. Policies vary among facilities and may include requesting immediate recollection and retesting by the laboratory or retesting using a rapid Point of Care instrument at the bedside.

  • Note and immediately report to the health-care provider (HCP) any critically increased or decreased values and related symptoms, especially symptoms of fluid imbalance.

  • It is essential that a critical finding be communicated immediately to the requesting health-care provider (HCP). A listing of these findings varies among facilities.

  • Timely notification of a critical finding for lab or diagnostic studies is a role expectation of the professional nurse. Notification processes will vary among facilities. Upon receipt of the critical value the information should be read back to the caller to verify accuracy. Most policies require immediate notification of the primary HCP, Hospitalist, or on-call HCP. Reported information includes the patient’s name, unique identifiers, critical value, name of the person giving the report, and name of the person receiving the report. Documentation of notification should be made in the medical record with the name of the HCP notified, time and date of notification, and any orders received. Any delay in a timely report of a critical finding may require completion of a notification form with review by Risk Management.

  • Symptoms of hyperkalemia include irritability, diarrhea, cramps, oliguria, difficulty speaking, and cardiac arrhythmias (peaked T waves and ventricular fibrillation). Continuous cardiac monitoring is indicated. Administration of sodium bicarbonate or calcium chloride may be requested. If the patient is receiving an IV supplement, verify that the patient is voiding.

  • Symptoms of hypokalemia include malaise, thirst, polyuria, anorexia, weak pulse, low blood pressure, vomiting, decreased reflexes, and electrocardiographic changes (depressed T waves and ventricular ectopy). Replacement therapy is indicated.

Interfering factors

  • Drugs that can cause an increase in potassium levels include ACE inhibitors, atenolol, basiliximab, captopril, clofibrate in association with renal disease, cyclosporine, dexamethasone, enalapril, etretinate, lisinopril in association with heart failure or hypertension, NSAIDs, some drugs with potassium salts, spironolactone, succinylcholine, and tacrolimus.
  • Drugs that can cause a decrease in potassium levels include acetazolamide, acetylsalicylic acid, aldosterone, ammonium chloride, amphotericin B, bendroflumethiazide, benzthiazide, bicarbonate, captopril, cathartics, chlorothiazide, chlorthalidone, cisplatin, clorexolone, corticosteroids, cyclothiazide, dichlorphenamide, digoxin, diuretics, enalapril, foscarnet, fosphenytoin, furosemide, insulin, laxatives, metolazone, moxalactam (common when coadministered with amikacin), large doses of any IV penicillin, phenolphthalein (with chronic laxative abuse), polythiazide, quinethazone, sodium bicarbonate, tacrolimus, IV theophylline, thiazides, triamterene, and trichlormethiazide. A number of these medications initially increase the serum potassium level, but they also have a diuretic effect, which promotes potassium loss in the urine except in cases of renal insufficiency.
  • Leukocytosis, as seen in leukemia, causes elevated potassium levels.
  • False elevations can occur with vigorous pumping of the hand during venipuncture. Hemolysis of the sample and high platelet counts also increase potassium levels, as follows: (1) Because potassium is an intracellular ion and concentrations are approximately 150 times extracellular concentrations, even a slight amount of hemolysis can cause a significant increase in levels. (2) Platelets release potassium during the clotting process, and therefore serum samples collected from patients with elevated platelet counts may produce spuriously high potassium levels. Plasma is the specimen of choice in patients known to have elevated platelet counts.
  • False increases are seen in unprocessed samples left at room temperature because a significant amount of potassium leaks out of the cells within a few hours. Plasma or serum should be separated from cells within 4 hr of collection.
  • Specimens should never be collected above an IV line because of the potential for dilution when the specimen and the IV solution combine in the collection container, falsely decreasing the result. There is also the potential of contaminating the sample with the substance of interest, if it is present in the IV solution, falsely increasing the result.

Nursing Implications and Procedure

Potential nursing problems

ProblemSigns & SymptomsInterventions
Electrolyte imbalance (Related to metabolic imbalance associated with disease process)Excess: nausea, weak or irregular pulse; sudden collapse, cardiac arrest. Deficit: thirst; tetany; weakness; constipation; arrhythmias; hypotension; nausea; vomiting; anorexia; polyuria; mental depression; cardiac arrestCorrelate potassium imbalance with disease process, nutritional intake, renal function, medications; monitor ECG status; monitor for respiratory changes; minimize metabolic complications; provide a safe environment to prevent injury; collaborate with the pharmacist and HCP for appropriate pharmacologic interventions; adjust medication dosage to compensate for renal impairment; collaborate with dietician for dietary modifications; begin dialysis treatments if necessary (hemodialysis or peritoneal dialysis); reduce intake of high-potassium foods and dietary supplements
Health management (Related to complexity of health-care system; complexity of therapeutic management; altered metabolic process resulting in increased or decreased potassium; knowledge deficit; conflicted decision making; cultural family health patterns; barriers to healthy decisions; mistrust of HCP)Health choices are ineffective in making a difference on outcomes; increasing symptoms of illness; verbalizes that therapeutic regime is too difficult; patient and family do not support HCP’s suggestions for health improvement; refusal to follow recommended therapeutic regimeAssess effort to follow recommended regime; assess family or cultural factors that impact the success of the therapeutic regime; assess the patient’s self-assessment of his or her health status; include the patient and family in designing the plan of care; tailor the plan of care to the patient’s lifestyle; collaborate with the patient and family to develop a system of managing own health; focus on behaviors that will make the biggest positive impact on improved health
Fluid volume (Related to metabolic imbalances associated with disease process)Deficient: decreased urinary output, fatigue, and sunken eyes, dark urine, decreased blood pressure, increased heart rate, and altered mental status. Overload: edema, shortness of breath, increased weight, ascites, rales, rhonchi, and diluted laboratory valuesRecord daily weight and monitor trends; record accurate intake and output; collaborate with physician with administration of IV fluids to support hydration; monitor laboratory values that reflect alterations in fluid status (potassium, blood urea nitrogen, creatinine, calcium, hemoglobin, and hematocrit); manage underlying cause of fluid alteration; monitor urine characteristics and respiratory status; establish baseline assessment data; collaborate with physician to adjust oral and IV fluids to provide optimal hydration status; administer replacement electrolytes as ordered; monitor serum potassium levels
Activity (Related to compromised cardiac status; compromised renal status; weakness; lack of motivation; oxygen supply and demand imbalance)Verbal report of weakness; inability to tolerate activity; shortness of breath with activity; altered heart rate, blood pressure, and respiratory rate with activityAssess current level of physical activity; take baseline vital signs; trend vital signs with activity; assess response to activity; monitor for oxygen desaturation with activity; administer prescribed oxygen with activity; collaborate with physical therapy to support activity; monitor blood pressure for orthostatic changes; collaborate with the patient to establish activity goals and guidelines; pace activities to match energy stores; assist with self-care


  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist in evaluating electrolyte balance.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex. Especially note complaints of weakness and confusion.
  • Obtain a history of the patient’s cardiovascular, endocrine, gastrointestinal, genitourinary, immune, and respiratory systems; symptoms; and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
  • Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.


  • Potential complications: N/A
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement. Instruct the patient not to clench and unclench the fist immediately before or during specimen collection.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.


  • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Nutritional Considerations: Potassium is present in all plant and animal cells, making dietary replacement simple to achieve in the potassium-deficient patient.
  • Observe the patient for signs and symptoms of fluid volume excess related to excess potassium intake (hyperkalemia), fluid volume deficit related to active loss (hypokalemia), or risk of injury related to an alteration in body chemistry. Symptoms of hypokalemia and hyperkalemia include dehydration, diarrhea, vomiting, or prolonged anorexia.
  • Increased potassium levels may be associated with dehydration. Evaluate the patient for signs and symptoms of dehydration. Dehydration is a significant and common finding in geriatric patients and other patients in whom renal function has deteriorated.
  • Decreased potassium levels may occur in patients receiving digoxin or potassium-wasting diuretics. Potassium levels should be monitored carefully because cardiac arrhythmias can occur. Instruct the patient in electrolyte replacement therapy and changes in dietary intake that affect electrolyte levels, as ordered.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.
  • Patient Education

    • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP.
    • Recognize anxiety related to test results and answer any questions or address any concerns voiced by the patient or family.
    • Educate the patient regarding access to nutritional counseling services. Provide contact information, if desired, for the Institute of Medicine of the National Academies (www.iom.edu).
    • Teach energy conservation techniques.
    • Teach the appropriate use of assistive devices.
  • Expected Patient Outcomes

    • Knowledge
    • Describes the signs and symptoms of physical overactivity
    • States their understanding that monitoring of serum potassium levels will be necessary to maintain health
    • Skills
    • Demonstrates how to pace activities and conserve energies in the performance of the activities of daily living
    • Identifies and lists foods that can increase potassium levels
    • Attitude
    • Identifies concerns about activity tolerance
    • Complies with the recommendation to access community resources to support a structured activity plan

Related Monographs

  • Related tests include ACTH, aldosterone, anion gap, antiarrhythmic drugs, alveolar/arterial gradient, ANP, BNP, blood gases, BUN, calcium, carbon dioxide, chloride, complement, CBC hematocrit, CBC hemoglobin, CBC WBC count and differential, Coomb’s antiglobulin (direct and indirect), cortisol, CK and isoenzymes, creatinine, DHEAS, echocardiography, echocardiography transesophageal, fecal fat, glucose, G6PD, Ham’s test, haptoglobin, hemosiderin, insulin, ketones, lactic acid, lung perfusion scan, magnesium, osmolality, osmotic fragility, plethysmography, urine potassium, PFT, PK, renin, sickle cell screen, sodium, and US abdomen.
  • Refer to the Cardiovascular, Endocrine, Gastrointestinal, Genitourinary, Immune, and Respiratory systems tables at the end of the book for related tests by body system.
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