In dehydration, which lab pattern is most typical?

• A. Decreased BUN and Na
• B. Increased BUN and Na
• C. Normal BUN and Na
• D. Elevated chloride

Answer: (B)

In dehydration, the body is volume depleted, so kidneys receive less blood flow. That triggers a prerenal response where urea is reabsorbed more in an attempt to conserve water, causing BUN to rise. At the same time, loss of free water relative to salt tends to raise serum sodium, so hypernatremia can occur. Put together, the typical lab pattern during dehydration is an increased BUN with an increased sodium level.

This fits the idea that dehydration concentrates the blood and reduces renal perfusion, unlike scenarios with adequate or excess fluids where BUN and sodium would be normal or lower. A sole rise in chloride isn’t the defining pattern here, and a decrease or normal BUN would not reflect the hypovolemic state.