What investigations are recommended for a patient presenting with symptoms of infection or inflammation?

Recommended Investigations for Patients with Symptoms of Infection or Inflammation

For patients presenting with symptoms of infection or inflammation, a comprehensive panel of laboratory tests, imaging studies, and microbiological assessments should be performed based on the suspected site and severity of infection.

Laboratory Investigations

Blood Tests

• Complete blood count (CBC) with differential leukocyte count and platelet count - essential for assessing inflammatory response and potential neutropenia 1, 2
• C-reactive protein (CRP) - highly sensitive marker for inflammation that correlates with disease activity, especially in Crohn's disease 1, 3, 4
• Erythrocyte sedimentation rate (ESR) - useful inflammatory marker, though less sensitive than CRP for acute inflammatory conditions 1, 3
• Comprehensive metabolic panel including:
  • Serum electrolytes 1, 2
  • Liver enzymes (transaminases) 1, 2
  • Total bilirubin 1, 2
  • Renal function tests (blood urea nitrogen, creatinine) 1, 2
  • Serum albumin (to assess nutritional status and degree of inflammation) 1, 3
• Procalcitonin - particularly helpful in suspected bacterial infections and sepsis 5

Stool Tests

• Fecal calprotectin - highly sensitive marker for intestinal inflammation, especially useful in inflammatory bowel disease 3, 4
• Stool cultures to rule out infectious causes 1, 3
• Clostridium difficile toxin testing - mandatory when infectious diarrhea is suspected 1, 6
• Fecal lactoferrin - marker of intestinal inflammation 4

Microbiological Investigations

• At least two sets of blood cultures - one from each lumen of central venous catheter (if present) and one from peripheral vein 2
• Culture specimens from other suspected sites of infection as clinically indicated 2
• Screening for viral infections (CMV, hepatitis) when appropriate, particularly in immunocompromised patients 6, 3

Imaging Studies

For Abdominal/Gastrointestinal Symptoms

• Contrast-enhanced CT scan of abdomen and pelvis - key study for detecting abscesses, fistulae, and other complications 1, 3
• Plain abdominal radiograph - useful for detecting bowel obstruction, perforation, or toxic megacolon in severe cases 3, 4
• MR enterography - preferred modality for assessing small bowel disease extent and severity 4
• Ultrasound - useful for detecting fluid collections and abscesses, especially in acutely ill patients 4

For Respiratory Symptoms

• Chest radiograph - mandatory for patients with respiratory signs or symptoms 2
• CT scan of chest - for further evaluation of abnormal findings on chest radiograph 2

For Suspected Spinal Infection

• MRI without and with IV contrast of affected spinal area - highest sensitivity (96%) and specificity (94%) for spine infection 7
• CT scan with IV contrast - useful particularly after surgical or interventional procedures 7

For Inflammatory Bowel Disease

• Flexible sigmoidoscopy or colonoscopy with biopsies - allows assessment of disease activity and collection of samples for histology 1, 3
• Endoscopic scoring tools (CDEIS, SES-CD) for precise documentation of lesions 4

Special Considerations

For Neutropenic Patients

• More frequent monitoring of CBC, CRP, and other inflammatory markers 2
• Lower threshold for imaging studies due to potentially attenuated inflammatory signs 2
• Consider CT of sinuses, abdomen, and pelvis as clinically indicated 2

For Diabetic Foot Infections

• Assessment of vascular supply (ankle-brachial index) 8
• Wound measurements and scoring (size, depth, undermining) 8
• Evaluation for proximal spread of infection 8

Monitoring Parameters

• Inflammatory markers (CRP, ESR) should be reassessed to monitor disease activity and treatment response 4
• Repeat imaging should be performed based on clinical response and disease severity 4
• For inflammatory bowel disease, endoscopic evaluation should be performed to assess ongoing disease activity when other objective evidence is absent 4

Pitfalls to Avoid

• Do not delay treatment while awaiting culture results in severely ill patients 3, 2
• Remember that normal inflammatory markers do not exclude infection, especially in immunocompromised patients 2
• Be aware that signs and symptoms of inflammation may be attenuated in neutropenic patients 2
• Recognize that normal radiographs do not rule out early discitis or spinal infection 9

By systematically applying these investigations based on clinical presentation, clinicians can effectively diagnose and monitor infections and inflammatory conditions, leading to improved patient outcomes.