What lab should you check for athletes on lithium to assess dehydration?

• A. Specific gravity to assess for dehydration (dehydration is >1.015)
• B. Hematocrit
• C. Serum sodium
• D. Creatinine clearance

Answer: (A)

Urine concentration reflects hydration status. Specific gravity measures how concentrated the urine is; when someone is dehydrated, the kidneys conserve water and urine becomes more concentrated, typically yielding a value above 1.015. In athletes, this quick, practical test gives a direct read on whether they're dehydrated, and it remains useful even in people taking lithium, who may have altered urine handling. Other labs don’t target hydration as directly: hematocrit can rise with fluid loss but is affected by many factors; serum sodium can be influenced by intake and other issues; creatinine clearance reflects kidney filtration over time rather than immediate hydration status. So checking urine specific gravity provides the most straightforward assessment of dehydration in this context.