The nurse observes that a client is experiencing melena. Which serum laboratory test should the nurse monitor in response to this finding?

A. Blood urea nitrogen (BUN): Elevated BUN can indicate kidney problems, but it's not the primary test for melena (black, tarry stools) which suggests upper gastrointestinal bleeding.B. Glucose: Glucose levels might be abnormal in some conditions that can cause bleeding, but it's not the most specific test for melena.C. White blood cell count (WBC): WBC might be elevated in response to infection or inflammation, but it's not the most specific test for melena.D. Hematocrit: Hematocrit measures the percentage of red blood cells in the blood. Melena can indicate significant blood loss, and monitoring hematocrit helps assess the severity of bleeding and potential need for blood transfusions.