Why lab data can be misleading in hypovolemia

摘要

Dr Rutecki's thoughtful note, "Diagnosing Dehydration: What Would Osier Do?" resonated strongly with me. I would add 2 domains in which review of the laboratory data in isolation will be most misleading, if we utilize an elevated BUN:creatinine ratio as a marker of hypovolemia-related prerenal azotemia: If poor food intake has coexisted with poor fluid intake, there is inadequate substrate for urea synthesis, and hence the BUN is falsely lowered, and the ratio fails to reflect the degree of extracellular fluid depletion. If substantial GI bleeding has occurred, the BUN will be falsely and unduly elevated, and the patient may be adjudged more hypovolemic than he or she actually is. Of course, a rectal examination with a test of the stool for either macroscopic blood or melena, or fecal occult blood, will help determine whether this artifact is present or absent.