A patient has been taking heparin for three days and has developed hematuria. The most appropriate action for the nurse is to:

A. Insert a urinary catheter to determine the residual urine. Inserting a urinary catheter may be necessary to accurately measure urinary output and assess for signs of urinary retention. However, the presence of hematuria suggests a potential bleeding complication related to heparin therapy. While monitoring urinary output is important, inserting a urinary catheter should not be the first action taken in response to hematuria. Other interventions to address the bleeding should be prioritized.

B. Hold the next dose of heparin and contact the physician. This is the correct answer. Hematuria can be a sign of a bleeding complication, which is a known side effect of heparin therapy. Holding the next dose of heparin is appropriate to prevent further bleeding, and contacting the physician ensures prompt evaluation and appropriate management of the patient's condition. The physician may decide to adjust the dose of heparin, temporarily discontinue it, or order further investigations to determine the cause of the hematuria.

C. Instruct the patient to drink adequate amounts of fluid. While maintaining hydration is important for overall health, instructing the patient to drink fluids would not directly address the underlying cause of hematuria, which may be related to a bleeding complication from heparin therapy. Holding the next dose of heparin and contacting the physician are more appropriate actions in response to hematuria.

D. Administer an additional dose of heparin subcutaneously. Administering additional heparin would exacerbate the bleeding risk and is contraindicated in the presence of hematuria. It is important to withhold further doses of heparin and seek medical guidance to address the bleeding complication.