Which laboratory pattern is typical for hypoosmolar hypervolemic hyponatremia?

Which laboratory pattern is typical for hypoosmolar hypervolemic hyponatremia?

• A. uNa <10; BUN/Cr >20:1; urine osmolal >450
• B. uNa >40; BUN/Cr <10:1; osmolal <100
• C. uNa 20; BUN/Cr 15:1; osmolal 350
• D. uNa 5; BUN/Cr 25:1; osmolal 600

Answer: (A)

In hypoosmolar hyponatremia with hypervolemia, the body effectively behaves as if it is volume-depleted even though total body fluid is increased. This triggers ADH release and RAAS activation, so the kidneys hold onto water and sodium to preserve perfusion. You see a very concentrated urine (urine osmolality high, typically well above 450 mOsm/kg) because water is being reabsorbed under the influence of ADH. The kidney also reabsorbs sodium to retain volume, so the urine sodium becomes very low (often less than 10 mEq/L). The reduced effective arterial volume also raises urea reabsorption relative to creatinine, giving a BUN/creatinine ratio greater than 20:1. Thus, the pattern of a very low urine sodium, a BUN/Cr ratio >20:1, and a highly concentrated urine fits this scenario best.

In hypoosmolar hyponatremia with hypervolemia, the body effectively behaves as if it is volume-depleted even though total body fluid is increased. This triggers ADH release and RAAS activation, so the kidneys hold onto water and sodium to preserve perfusion. You see a very concentrated urine (urine osmolality high, typically well above 450 mOsm/kg) because water is being reabsorbed under the influence of ADH. The kidney also reabsorbs sodium to retain volume, so the urine sodium becomes very low (often less than 10 mEq/L). The reduced effective arterial volume also raises urea reabsorption relative to creatinine, giving a BUN/creatinine ratio greater than 20:1.

Thus, the pattern of a very low urine sodium, a BUN/Cr ratio >20:1, and a highly concentrated urine fits this scenario best.