Potassium (K+)is an essential electrolyte and mineral. Hyperkalemia is a condition in which the potassium levels in the blood have increased. Hyperkalemia diagnosis is confirmed when the serum potassium level exceeds the plasma potassium concentration by more than 0.5 mmol/L. It can be mild, moderate, or severe according to serum potassium levels.
The normal potassium level for an adult ranges from 3.5 to 5.2 mEq/L (3.5 to 5.2 mmol/L).
- Mild hyperkalemia — 5.5 to 6.5 mmol/l
- Moderate — 6.5 to 7.5 mmol/l
- Severe — >7.5 mmol/l. These levels can lead to significant hemodynamic and neurologic complications.
Hyperkalemia results either from the shift of potassium from within the cells to out of cells or from inadequate potassium excretion from the kidneys. This post describes the various methods and tests used to diagnose hyperkalemia.
98% of this electrolyte is found inside the cells (described as intracellular) of the tissues, organs, etc. 75% of this intracellular potassium is found in muscle cells.
A balance of only 2% is present in the extracellular fluid and blood plasma. This proportion of intracellular to extracellular potassium is essential for the normal functioning of the neurons, skeletal muscles, and cardiac muscles.
With hyperkalemia, symptoms may be absent and when present they are not specific and that’s what makes hyperkalemia diagnosis difficult. In view of its possible fatal dangerous outcome, early diagnosis becomes important after which prompt treatment must follow.
A suspicion of hyperkalemia can be obtained from the medical history, symptoms if any, and physical examination. Confirmation can be obtained only from the lab tests and ECG changes.
Medical history
Taking medical history helps to find out if the patient is exposed to any hyperkalemia risk factors and causes. This is the first step out of others in hyperkalemia diagnosis.
- The medical history of the patient includes gathering relevant information about the patient.
- Regarding his eating habits and exclusive affinity to certain foods that could be high in potassium. Excessive intake of potassium can cause hyperkalemia usually in the presence of impaired renal function
- Whether he is a heart patient or has hypertension or diabetes and is on a heart-healthy diet with low sodium and high potassium foods
- Whether he/she is taking any drugs that could cause this condition.
- Whether he is on potassium supplements, salt substitutes, and such additives that are high in potassium.
- Whether he has had any kidney problems.
Physical examination
- Vital signs are usually normal. These include blood pressure, pulse, respiratory rate, and temperature.
- Your doctor will place a stethoscope on your chest to listen to your heartbeats. He will specifically listen for signs of arrhythmia.
- The general finding may show muscle weakness and fatigue.
- Slow heart rate (bradycardia)
- Tachypnea (rapid breathing) due to respiratory muscle weakness.
- Depressed or absent deep tendon reflexes.
Diagnostic tests
Diagnostic lab tests for hyperkalemia are done on blood and urine. They include:
- Serum potassium to determine its level in blood.
- Kidney function tests to rule out kidney insufficiency.
- In case of renal failure, serum calcium is checked because hypocalcemia can cause cardiac rhythm changes
- Complete blood count (CBC) with platelet count
- A comprehensive metabolic panel is a blood test, which measures your sugar (glucose) level, electrolyte and fluid balance, kidney function, and liver function.
- Arterial blood gases to rule out acidosis
- Serum creatinine phosphokinase (CPK) and calcium level measurements to rule out rhabdomyolysis (breakdown of skeletal muscle tissue).
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Digoxin level – If the patient is on a digitalis
- Your doctor may ask for urine studies for potassium, sodium, and osmolality. Urine potassium can be tested in a single urine sample, but it is more often measured in a 24-hour urine sample. For adults, normal urine potassium values are generally 20 mEq/L in a random urine sample and 25 to 125 mEq per day in a 24-hour collection.
ECG changes in hyperkalemia
Electrocardiogram (ECG) is done to check for changes indicative of hyperkalemia. These include the peaked T-wave, flattened P-wave with prolonged PR interval, or a totally absent P-wave, and wide QRS complex. St depression is another important feature.
These changes are more indicative of potassium levels of 6.5-8.0 mEq/L. These ECG changes reverse with the success of the appropriate treatment. However, a normal EKG may be seen even with severe hyperkalemia.
Pseudohyperklaemia is a condition in which the blood tests show high potassium levels in spite of it being normal. Exclude pseudohyperkalemia in patients who have a normal electrocardiogram and no risk factors for the development of hyperkalemia.
It happens due to poor technique or practice during the collection and preanalytic processing of blood samples in the laboratory. This is ruled out by correlating with the medical history, ECG findings, and retesting the blood.