Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1142 page)

   Chilling whole blood beyond 2 hours

   Prolonged tourniquet use and hand exercise when drawing blood

   Potassium value can be elevated approximately 15% in slight hemolysis (Hb ≤50 mg/dL) and elevated approximately 30–50% in moderate hemolysis (Hb >100 mg/dL). Therefore, potassium status can be assessed in those with slight hemolysis but not in those with moderate hemolysis.

   Excess dietary intake or rapid potassium infusion.

   Drugs with high potassium content (e.g., 1 million units of penicillin G potassium contains 1.7 mmol of potassium).

   Transfusion of old blood.

POTASSIUM, URINE

   Definition

   Urinary potassium levels are helpful in the evaluation of patients with unexplained hypokalemia, electrolyte, and acid–base balance. In the presence of such hypokalemia, urine excretion is helpful to separate renal from nonrenal losses. Excretion <20 mmol/24 hours is evidence that hypokalemia is not from renal loss. Renal loss >50 mmol/L in a hypokalemic, and hypertensive patient not on a diuretic may indicate primary or secondary aldosteronism.

   
Normal range:

   Twenty-four–hour urine:

   Male:

•   Less than 10 years: 17–54 mmol/day

•   10–14 years: 22–57 mmol/day

•   Greater than 14 years: 25–125 mmol/day

   Female:

•   6–10 years: 8–37 mmol/day

•   10–14 years: 18–58 mmol/day