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

Choice A Reason: White blood cell count (WBC) is inappropriate. White blood cell count is typically monitored to assess for signs of infection or inflammation. While it's important to monitor WBC count in certain situations, such as suspected infection, melena itself is not directly indicative of an increased risk of infection. Therefore, monitoring WBC count may not be the most immediate response to the finding of melena. Choice B Reason: Glucose is inappropriate. Glucose monitoring is essential for patients with diabetes or those at risk of hypoglycemia or hyperglycemia. However, melena is not directly related to glucose metabolism or regulation. Therefore, monitoring glucose levels would not be the most relevant response to the finding of melena. Choice C Reason: Blood urea nitrogen (BUN) is inappropriate. Blood urea nitrogen is often monitored to assess kidney function and hydration status. While severe bleeding can potentially lead to hypovolemia and prerenal azotemia (elevated BUN due to decreased renal perfusion), monitoring BUN would not be the immediate response to the finding of melena. Instead, assessing for signs of hypovolemia and monitoring other markers of blood loss, such as hematocrit, would be more appropriate. Choice D Reason: Hematocrit is appropriate. Melena refers to the passage of black, tarry stools containing blood that has been digested. It indicates upper gastrointestinal bleeding, typically from the stomach or upper small intestine. Monitoring the hematocrit level is important because significant bleeding, as indicated by melena, can lead to a decrease in the hematocrit level due to the loss of red blood cells and plasma volume. Monitoring the hematocrit helps assess the severity of the bleeding and guides treatment decisions, such as the need for blood transfusions. Therefore, the nurse should monitor the hematocrit level in response to the finding of melena.