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HelpMayo Test ID RKUR Potassium, Random, Urine
Specimen Required
Supplies: Sarstedt 5 mL Aliquot Tube (T914)
Container/Tube: Plastic, 5-mL tube
Specimen Volume: 4 mL
Collection Instructions:
1. Collect a random urine specimen.
2. No preservative.
Useful For
Determining the cause for hyper- or hypokalemia using a random urine specimen
Method Name
Potentiometric, Indirect Ion-Selective Electrode (ISE)
Reporting Name
Potassium, Random, USpecimen Type
UrineSpecimen Minimum Volume
1 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Urine | Refrigerated (preferred) | 14 days | |
| Frozen | 30 days | ||
| Ambient | 7 days |
Reject Due To
| All specimens will be evaluated at Mayo Clinic Laboratories for test suitability. |
Clinical Information
Potassium (K+) is the major intracellular cation. Functions of K+ include regulation of neuromuscular excitability, heart contractility, intracellular fluid volume, and hydrogen ion concentration. The physiologic function of K+ requires the body to maintain a low extracellular fluid (ECF) concentration of the cation; the intracellular K+ concentration is 20 times greater than the extracellular concentration. Only 2% of total body K+ circulates in the plasma.
The kidneys provide the most important regulation of K+. The proximal tubules reabsorb almost all the filtered K+. Under the influence of aldosterone, the remaining K+ can then be secreted into the urine in exchange for sodium in both the collecting ducts and the distal tubules. Thus, the distal nephron is the principal determinant of urinary K+ excretion.
Decreased excretion of K+ in acute kidney disease and end-stage kidney failure are common causes of prolonged hyperkalemia.
Renal losses of K+ may occur during the diuretic (recovery) phase of acute tubular necrosis, during administration of non-potassium sparing diuretic therapy, and during states of excess mineralocorticoid or glucocorticoid.
Reference Values
No established reference values
Random urine potassium may be interpreted in conjunction with serum potassium, using both values to calculate fractional excretion of potassium.
The calculation for fractional excretion (FE) of potassium (K) is
FE(K)= ([K(urine) X Creat(serum)]/[K(serum) X Creat(urine)]) X 100
Interpretation
Hypokalemia reflecting true total body deficits of potassium (K+) can be classified into renal and nonrenal losses based on the daily excretion of K+ in the urine. During hypokalemia, if urine excretion of K+ is less than 30 mEq/day, it can be concluded that renal reabsorption of K+ is appropriate. In this situation, the causes for the hypokalemic state are either decreased K+ intake or extra renal loss of K+ rich fluid. Urine excretion of more than 30 mEq/day in a hypokalemia setting is inappropriate and indicates that the kidneys are the primary source of the lost K+.
Cautions
Ion-selective electrodes are selective for the ion in question but are not specific. Other monovalent cations may interfere but not in the physiologic range.
Clinical Reference
1. Delaney MP, Lamb EJ: Kidney disease. In: Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018:1308-1309
2. Toffaletti J: Electrolytes. In: Dufour DR, Rifai N, eds. Professional Practice in Clinical Chemistry: A Review. AACC Press; 1993
Method Description
The ion-selective electrode (ISE) module performs indirect measurement of electromotive force (EMF). The ISE module measures the EMF difference between an ion-selective electrode and a reference electrode. The EMF of the ion-selective electrode is dependent on the ion concentration of the sample. The EMF of the reference electrode is constant. An electronic calculation circuit converts EMF of the sample to the ion concentration of the sample.(Package insert: Potassium. Roche Diagnostics; V14.0 02/2018)
Specimen Retention Time
7 daysPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Test Classification
This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.CPT Code Information
84133
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| RKUR | Potassium, Random, U | 2828-2 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| RKUR | Potassium, Random, U | 2828-2 |
Day(s) Performed
Monday through Sunday