How Hyperkalemia Is Diagnosed

When your serum potassium level is 5.5 mEq/L or higher, you may be diagnosed with hyperkalemia. The condition can be caused by ingesting too much potassium (eating or drinking), not excreting enough potassium (urinating, stooling, or sweating), or by potassium leaking out of cells.

Testing can help to determine which of these mechanisms is triggering your high potassium. Only when you know why you have hyperkalemia can you treat it properly and hopefully prevent recurrences.

Blood Tests

Before you go down the path of a formal evaluation, your healthcare provider will want to make sure you have true hyperkalemia.

A tourniquet that is applied too tightly or too long can cause the red blood cells to hemolyze or burst, leaking potassium into the specimen. Repeated clenching of the fist during venipuncture can also cause potassium to leak out of your cells, increasing your lab results by as much as 1 to 2 mEq/L.

Your healthcare provider's first task is to recheck your potassium level. If your levels remain high, they may order the following tests.

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Initial Tests

Renal failure, whether it is acute or chronic, is one of the most common causes of hyperkalemia. When the kidneys fail, they are not able to excrete potassium properly. This can lead to the build-up of potassium in the blood.

Blood urea nitrogen (BUN) and creatinine measure how well your kidneys are functioning and are included as part of the basic metabolic panel. Other tests in the panel include sodium, chloride, bicarbonate, and glucose. These lab values are used to calculate an anion gap that, if elevated, indicates metabolic acidosis.

Acidosis can draw potassium out of cells and into the blood. High glucose levels, as can be seen in uncontrolled diabetes, can do the same. Low sodium levels in the face of high potassium levels can suggest a hormonal condition known as hypoaldosteronism.

A complete blood count can also be a helpful screening test. The white blood count can be a sign of infection or inflammation in the body. Low hemoglobin and hematocrit levels reflect anemia. Anemia caused by the breakdown of red blood cells, also known as hemolytic anemia, can release high levels of potassium into the blood.

Specific Tests

Depending on your symptoms and medical history, your healthcare provider may also choose to pursue some of the following tests. 

• Aldosterone: Aldosterone is a hormone produced by the adrenal gland that regulates blood pressure. If potassium levels are high and sodium levels are low, an aldosterone level may be needed to confirm a diagnosis of hypoaldosteronism, i.e., too little aldosterone. Hypotension is also common with the condition.
• Creatinine phosphokinase (CPK): High levels of CPK suggest that there has been an injury to the muscles. Not only does this enzyme leak out of the muscles but it can flood the kidneys, leading to kidney failure in what is known as rhabdomyolysis. Potassium also leaks out of the muscle tissue.
• Digoxin levels: Digoxin is one of many medications that can have a side effect of hyperkalemia. This medication is often used to treat conditions like atrial fibrillation and congestive heart failure. Beta-blockers, also used to treat cardiac conditions, can increase serum potassium levels too. However, only digoxin has a blood test to check how much medication is in your bloodstream. These drug levels can be used to increase or decrease your medication dose to safe levels.
• Uric acid and phosphorus tests: When cells break down, they release uric acid and phosphorus in addition to potassium. This can occur in hemolytic anemia when blood cells burst or in flare-ups of sickle cell disease. It can also occur in tumor lysis syndrome when there is a ​massive breakdown of cells after chemotherapy.

Urine Tests

A simple urinalysis looks for blood, glucose, protein, or infection in the urine. Abnormal findings could indicate glomerulonephritis, inflammation of the kidney, or glomerulonephrosis, a non-inflammatory condition where the kidney leaks protein. It could also show diabetes that is uncontrolled.

More specific urine tests may be pursued to check how well the kidneys are performing. If urine secretion of potassium and sodium are within expected limits, the kidneys are not to blame. A non-renal cause ought to be investigated. Testing for urine myoglobin can confirm a diagnosis of rhabdomyolysis (see above).

Cardiac Tests

Hyperkalemia can trigger life-threatening arrhythmias if your potassium levels get too high. An electrocardiogram (ECG) is an important diagnostic tool, not only to detect more severe cases of hyperkalemia but to also identify what kind of arrhythmia is present.

An ECG measures the electrical conduction through the heart, from the top chambers of the heart, the atria, to the bottom chambers, the ventricles. Each line on an ECG from PQRST represents activation or recovery of a different chamber of the heart muscle.

As serum potassium increases, ECG changes become more severe. Starting at levels 5.5 meq/L and above, the ventricles may have difficulty recovering. This may be seen as peaked t-waves on ECG. Atrial activation is impacted at 6.5 mEq/L so that p-waves may no longer be seen. At 7.0 mEq/L, QRS waves are widened, corresponding with delayed activation of the ventricles.

Cardiac arrhythmias tend to develop at 8.0 mEq/L. This can include everything from sinus bradycardia to ventricular tachycardia. In the worst case scenario, asystole, loss of all electrical impulses, can occur and the heart stops.

Differential Diagnosis

People with cirrhosis, congestive heart failure, and diabetes are at higher risk for developing hyperkalemia. Other chronic conditions that can be a factor include amyloidosis and sickle cell disease.

If you are prescribed medications like ACE inhibitors, angiotensin-receptor blockers, beta-blockers, cyclosporine, digoxin, minoxidil, spironolactone, and tacrolimus, be aware that your potassium levels could increase.

Your doctor may look for other causes of hyperkalemia, like renal failure and hypoaldosteronism, as outlined above.