Which laboratory test should the nurse monitor if the client has been vomiting and has had numerous episodes of diarrhea?

Serum potassium.

A. (incorrect) Serum calcium is decreased in conditions such as osteoporosis or post-thyroid surgery, but not in vomiting and diarrhea. B. (incorrect) Serum phosphorus levels are altered in acute and chronic renal failure or diabetic ketoacidosis, among other conditions, but not with acute fluid losses from the gastrointestinal tract. C. (correct) Clients lose potassium from the GI tract or through the use of diuretic medications. Potassium imbalances can lead to cardiac arrhythmias. D. (incorrect) The body is not at risk from losing sodium from these sources as it is with potassium. TEST-TAKING HINT: The nurse must recognize basic fluids and electrolytes in the body and the implications of excess or loss. The body holds onto sodium and releases potassium.