POTASSIUM

Centrifuge SST or PST after clotting to separate serum from cells.

If serum or plasma is not separated from the red cells promptly, potassium will leak from the red cells into the serum or plasma, causing an erroneous elevation of the concentration.  Hemolysis of the red cells will also cause erroneous elevation of the potassium concentration.

Potassium testing is frequently ordered, along with other electrolytes, as part of a routine physical. It is used to detect concentrations that are too high (hyperkalemia) or too low (hypokalemia). The most common cause of hyperkalemia is kidney disease, but many drugs can decrease potassium excretion from the body and result in this condition. Hypokalemia can occur if you have diarrhea and vomiting or if you are sweating excessively. Potassium can be lost through your kidneys in urine; in rare cases, potassium may be low because you are not getting enough in your diet.

 
Potassium concentrations may be ordered at regular intervals to monitor drugs that can cause your kidneys to lose potassium, particularly diuretics, resulting in hypokalemia. Monitoring may also be done if you have a condition or disease, such as acute or chronic kidney failure, that can be associated with abnormal potassium levels.