Electrolyte Abnormalities

An electrolyte result becomes clinically meaningful when it is connected to the patient's physiology. Ask four questions: What changed the concentration? What is the kidney doing? Is the abnormality affecting excitable tissue now? How quickly can treatment itself change the result? Kidney function, volume status, medications, acid-base balance and hormones determine whether an abnormal value reflects loss, retention, dilution or a shift between body compartments. The same potassium concentration can represent different risks in a patient with chronic kidney disease, a patient with diabetic ketoacidosis, or a patient taking a potassium-wasting diuretic. Symptoms and the ECG can outrank the number, while the trend may matter more than a single result. In Canadian practice, sodium and potassium are reported in mmol/L; calcium, phosphate and magnesium are also generally reported in SI units. Reference intervals vary by laboratory. When albumin or pH makes total calcium difficult to interpret, ionized calcium is more useful than relying on a correction formula. The sections that follow move from mechanism, to diagnostic discrimination, to treatment and prescribing surveillance.