Blood carries electrolytes, which are also found in urine and sweat. Which statement is true?

• A. True
• B. False
• C. Only in urine
• D. Only in sweat

Answer: (A)

Electrolytes are charged minerals that exist as ions in body fluids, and they are essential for fluid balance, nerve signaling, and muscle function. Blood carries a range of electrolytes—sodium, potassium, chloride, bicarbonate, calcium, and magnesium, among others. As the kidneys filter blood, they regulate these electrolyte levels, producing urine that reflects how the body is handling them. Sweat glands release a fluid that contains electrolytes as well, especially sodium and chloride, with smaller amounts of potassium, calcium, and magnesium. Because electrolytes are present in blood, urine, and sweat, the statement is true: electrolytes found in blood are also found in urine and sweat. Clinically, this underpins why blood tests measure electrolytes, why urine tests assess renal handling, and why sweat testing (such as for chloride in certain conditions) is used in specific contexts.