Potassium 

Potassium 

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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.

The reference ranges of serum/plasma potassium levels are as follows:

Adults: 3.5-5.1 mEq/L or mmol/L

Children: 3.4-4.7 mEq/L or mmol/L (age dependent)

The reference ranges of urinary potassium levels are as follows:

Adults: 25-125 mEq/L/day

Children: 10-60 mEq/L/day

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

Conditions associated with high potassium values include the following:

Hyperkalemia

Blood transfusion

Hemolytic anemia (red cell destruction)

Acute renal failure

Addison disease

Hypoaldosteronism

Tissue injury

Eating disorders (anorexia, bulimia)

Infection

Diabetic ketoacidosis

Dehydration

Excessive potassium intake (dietary or intravenous)

Magnesium deficiency

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. [1] Because hyperkalemia can cause lethal cardiac arrhythmia, 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, renal failure) or low (eg, pyloric stenosis, alkalosis).

Conditions associated with low potassium values include the following:

Hypokalemia

Dehydration

Vomiting

Diarrhea

Hyperaldosteronism

Deficient potassium intake

Acetaminophen overdose

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. Question the patient regarding (1) diarrhea and use of laxatives; (2) diet and total parenteral nutrition contents; and (3) the use of insulin, excessive bicarbonate supplements, and episodic weakness.

A high urine potassium level (>40 mEq/L) suggests renal loss. Examine the patient’s medication list. 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.

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 renal 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 renal 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 renal conservation of potassium, while values above that indicate some degree of renal 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 failure

Cushing syndrome

Diabetic ketoacidosis

Primary thrombocythemia

Rhabdomyolysis

Thyrotoxic periodic paralysis

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

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.

The normal level of potassium has a narrow range, as it is critical to the function of nerve and muscle cells, including 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. If sodium levels go down, potassium levels go up. Potassium levels are also affected by the hormone aldosterone, which is produced by the adrenal glands. 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.

Potassium blood tests are important in the diagnosis and treatment of patients with hypertension, renal failure or impairment, cardiac distress, disorientation, dehydration, nausea, and diarrhea. Some causes of increased potassium values include renal glomerular disease, adrenocortical insufficiency, diabetic ketoacidosis, sepsis, and in vitro hemolysis. Some 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 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

The physician should ask the patient about any medications being taken. 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 cause loss of potassium. Low urine potassium levels may result from the use of glucocorticoids or nonsteroidal anti-inflammatory drugs.

Shaffer SG, Kilbride HW, Hayen LK, Meade VM, Warady BA. Hyperkalemia in very low birth weight infants. J Pediatr. 1992 Aug. 121(2):275-9. [Medline].

Choi MJ, Ziyadeh, FN. The Utility of the Transtubular Potassium Gradient in the Evaluation of Hyperkalemia. J Am Soc Nephrol. 2008;19:424-426.

Kamel KS, Ethier JE, Quaggin S, Levin A, Albert S, Carlisle EJ, et al. Studies to determine the basis for hyperkalemia in recipients of a renal transplant who are treated with cyclosporine. J Am Soc Nephrol. 1991;2:1279-1284.

Mayan H, Kanto R, Farfel Z. Trans-tubular potassium gradient in patients with drug-induced hyperkalemia. Nephron. 2001;89:56-61.:

Lim YS, Han JS, Kim KA, Yoon JH, Kin CY, Lee HS. Monitoring of transtubular potassium gradient in the diuretic management of patients with cirrhosis and ascites. J Am Soc Nephrol. 2002;22:426-432.

Edgar V Lerma, MD, FACP, FASN, FAHA, FASH, FNLA, FNKF Clinical Professor of Medicine, Section of Nephrology, Department of Medicine, University of Illinois at Chicago College of Medicine; Research Director, Internal Medicine Training Program, Advocate Christ Medical Center; Consulting Staff, Associates in Nephrology, SC

Edgar V Lerma, MD, FACP, FASN, FAHA, FASH, FNLA, FNKF is a member of the following medical societies: American Heart Association, American Medical Association, American Society of Hypertension, American Society of Nephrology, Chicago Medical Society, Illinois State Medical Society, National Kidney Foundation, Society of General Internal Medicine

Disclosure: Author for: UpToDate, ACP Smart Medicine, Elsevier, McGraw-Hill, Wolters Kluwer.

Eric B Staros, MD Associate Professor of Pathology, St Louis University School of Medicine; Director of Clinical Laboratories, Director of Cytopathology, Department of Pathology, St Louis University Hospital

Eric B Staros, MD is a member of the following medical societies: American Medical Association, American Society for Clinical Pathology, College of American Pathologists, Association for Molecular Pathology

Disclosure: Nothing to disclose.

Potassium 

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