What diagnostic tests and treatment should be done for a 46-year-old male with intermittent abdominal pain, signs of infection, diarrhea, and impaired renal function?

Diagnostic Tests for 46-Year-Old Male with Intermittent Abdominal Pain

For a 46-year-old male with generalized abdominal pain, signs of infection, diarrhea, and urinary symptoms, a contrast-enhanced CT scan of the abdomen and pelvis should be the primary diagnostic test, followed by comprehensive laboratory testing including complete blood count, renal function tests, and stool studies.

Initial Laboratory Tests

• Complete blood count (CBC) to assess for leukocytosis and evaluate the severity of infection 1
• Comprehensive metabolic panel including electrolytes, renal function (BUN, creatinine), and liver function tests to evaluate for organ dysfunction 1
• C-reactive protein (CRP) and/or other inflammatory markers to assess severity of inflammation 1, 2
• Urinalysis to evaluate for urinary tract infection given the patient's urinary symptoms 2
• Serum lipase to rule out pancreatitis 2
• Blood cultures, especially given the history of fever and signs of infection 1
• Stool studies including tests for infectious pathogens, given the history of diarrhea 1

Imaging Studies

• Contrast-enhanced CT scan of the abdomen and pelvis is the most appropriate initial imaging study for this patient with generalized abdominal pain 1
• CT has the highest sensitivity and specificity for evaluating acute abdominal pain and can identify a wide range of pathologies including abscess, bowel obstruction, diverticulitis, and appendicitis 1, 3
• Conventional radiography (plain films) has limited diagnostic value and should not be the primary imaging modality 1, 4
• If CT is unavailable or contraindicated, ultrasonography can be considered as an alternative initial imaging study 4

Special Considerations

• Given the patient's history of diarrhea, specific testing for Clostridioides difficile and its toxin should be performed, especially considering recent antibiotic use 1
• The patient's urinary symptoms (straining, hesitancy, decreased amount) warrant evaluation for possible urologic issues, which can be assessed with the CT scan 2
• If mesenteric ischemia is suspected based on the severe abdominal pain and clinical picture, CT angiography should be considered 1
• For this patient with signs of infection and abdominal pain, blood cultures are important to rule out bacteremia 1

Diagnostic Algorithm

1. Stabilize the patient and assess vital signs to determine the presence of sepsis or shock 1
2. Obtain laboratory tests (CBC, CMP, CRP, urinalysis, lipase, blood cultures)
3. Proceed with contrast-enhanced CT of abdomen and pelvis 1
4. Collect stool samples for microbiological testing including C. difficile 1
5. Consider additional specialized testing based on CT findings and clinical suspicion:
   • If biliary pathology is suspected: add hepatobiliary iminodiacetic acid (HIDA) scan
   • If mesenteric ischemia is suspected: CT angiography 1
   • If urologic pathology is suspected: consider additional urologic evaluation

Pitfalls to Avoid

• Relying solely on laboratory tests without imaging, as they are insufficient to discriminate between urgent and non-urgent diagnoses 4
• Delaying imaging in a patient with persistent severe abdominal pain and signs of infection 1
• Using plain radiographs as the primary imaging modality due to their limited diagnostic value 1, 4
• Failing to consider extra-abdominal causes of abdominal pain 2
• Overlooking the possibility of C. difficile infection in a patient with recent antibiotic use and diarrhea 1

This comprehensive diagnostic approach will help identify the underlying cause of this patient's abdominal pain, allowing for appropriate and timely treatment to improve outcomes related to morbidity and mortality.