Healthy potassium levels are essential to proper nervous system function. If you are experiencing symptoms of low potassium levels or undergoing a medical treatment known to affect potassium concentration, your physician may prescribe a blood test. If the results indicate low potassium levels in the blood, the physician will prescribe a urine test to affirm or rule out possible conditions.

Function of Potassium

Potassium (atomic symbol K) ions are part of a major class of chemicals in the human body known as electrolytes. Potassium plays a major role in regulating the amount of water the body retains and is used to create ionic concentration gradients that allow muscles to contract and nerves to carry signals along the central nervous system. The body naturally regulates potassium levels through a feedback system involving the hormone aldosterone, sodium ions and the kidneys. When one begins experience symptoms of potassium deficiency (e.g., cramps, dehydration, diarrhea, frequent urination, low blood pressure and irregular heart rhythms), it may be a sign that the kidneys or adrenal glands aren't functioning properly. Certain chemotherapy treatments can lead to unsafe drops in potassium levels as well; therefore, an oncologist may order a potassium level test to monitor how a patient's body is responding to that particular treatment.

Blood Test

Because the kidneys will expel potassium regardless of its concentration in the blood, doctors test the blood directly to determine whether a potassium problem exists. First, a nurse will tie a tourniquet around your arm at the bicep, causing the arm's veins to swell slightly. After swabbing the injection site with cotton soaked in alcohol, the nurse inserts the needle into the vein. Anywhere from one to three vials of blood will be taken; besides testing potassium levels, the laboratory will test for other electrolyte (e.g., magnesium, sodium, chloride, calcium and phosphate) levels. If your K levels turn out to be normal or too high, these additional electrolyte levels might help explain your symptoms. If your K levels turn out to be too low, the other electrolyte levels can point to the specific cause of your deficiency.

Urine Test

If your blood test shows low potassium levels, the doctor will order a urine test. Malfunctioning kidneys fail to reabsorb potassium as they filter the blood; instead, this potassium is expelled in the urine, depleting blood of this crucial electrolyte. After obtaining a 20-ml sample of urine, the nurse submits the specimen to the lab. If the tests demonstrate normal levels of potassium in the urine, the doctor can rule out kidney failure, narrowing the range of possible conditions.

Source:

Testing Potassium Levels