Final answer:
The next step in evaluating a male >40 smoker with asymptomatic microscopic hematuria is to perform a urine culture to rule out a urinary tract infection before considering other diagnostic procedures such as cystoscopy or ultrasound.
Step-by-step explanation:
The next step in the management of a male patient over 40 who is a smoker with asymptomatic microscopic hematuria (3-5 RBC/hpf) is to ensure that the hematuria is not due to a urinary tract infection (UTI). Therefore, a urine culture should be performed to rule out infection. This is important because microscopic hematuria can be caused by many conditions, including nephritis, trauma, tuberculosis of the kidney, and kidney stones. Additionally, the presence of urethral or bladder cancer must be considered, especially in a patient with risk factors such as age over 40 and smoking history.
While cystoscopy, abdominal ultrasound, and observation with repeat urinalysis are potential options for further evaluation, the first step after finding asymptomatic microscopic hematuria should be a urine culture to confirm or exclude a UTI as the cause. This is because the sensitivity and specificity of urinalysis alone can lead to false positive or negative results for infections; thus, a culture is a more accurate method to confirm a UTI. After ruling out a UTI, further diagnostic steps can be taken based on the urine culture results and clinical judgment.