- The clinical utility of the serum potassium test includes:
- To detect hypo or hyperkalemia (low or high potassium)
- To evaluate and monitor renal function, acid-base balance, and glucose metabolism
- To evaluate of electrolyte imbalances in:
- Acidotic or alkalotic states
- Elderly patients
- Patients on medications known to affect potassium
- Patients on hyperalimentation or dialysis
- Trauma
- Burns
- As part of evaluation of cardiac arrhythmias
- For routine screening of electrolytes in acute and chronic illness
- To evaluate neuromuscular and endocrine disorders
- To evaluate clinical signs of hyperkalemia or hypokalemia
- Screening in hypertensive patients
- Evaluate the response and efficacy of treatment for abnormal potassium levels
- Potassium has a significant and inverse relationship to pH: A decrease in pH of 0.1 increases the potassium level by 0.6 mEq/L
- Dietary intake of at least 40 mEq/day is essential
Additional information
- Normal day to day variation is 1-2%
- Variation of potassium levels within a given day can be as much as 20%, with a peak at 8.00 AM and decreasing during the day
- Related laboratory tests include:
- Aldosterone
- Anion gap
- Antiarrhythmic drugs
- Arterial blood gas
- Bicarbonate
- Blood gases
- Calcium
- Chloride
- Creatine kinase
- Electrolytes
- Osmolality
- Potassium (Urine)
- pH of blood
- Potassium, urine
- Serum creatinine
- Sodium (blood and urine)
Hyperkalemia (High potassium) EKG Findings:
- EKG findings suggestive of hyperkalemia include:
- Peaked T waves
- 2nd or 3rd degree AV block
- Loss of P waves or sine waves
- Changes are typically related to severity of the hyperkalemia
- As hyperkalemia worsens, the pattern is that of QRS widening with merging of the QRS and T waves, with the "sine wave" of hyperkalemia
- 5.5-6.5 mEq/L à Tall, peaked T-waves, shortened QT interval, ST segments can disappear
- >7 mEq/L à Decreased P wave amplitude, wide P-waves
- >8 mEq/L à Absent P-waves (e.g. sinus arrest), A-V block, QRS widening, ventricular tachycardia, ventricular fibrillation or "cardiac standstill"
Hypokalemia (Low potassium) EKG Findings:
- EKG findings suggestive of hypokalemia include:
- Flat T-wave
- ST depression
- Prominent U-waves
- Prolonged QT
- QRS complexes may widen when potassium drops below 3 mEq/L
- With progression of hypokalemia, these U waves reach "giant" size and fuse with the T waves as the potassium level drops to 1 mEq/L
- Severe hypokalemia or hypokalemia with concurrent digoxin use; Ventricular tachycardia or fibrillation may occur
Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.
| Conv. units
(mEq/L) | SI units
(mmol/L) |
|---|
| Adults | 3.5–5.2 | 3.5–5.2 |
| Children 1-17 years | 3.3–4.7 | 3.3–4.7 |
| Infants <1 year | 3.3–6.0 | 3.3-6.0 |
Neonates  7 days | 3.6–6.0 | 3.6–6.0 |
| Critcal Values | <2.5 | <2.5 |
| >7.0 | >7.0 |
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