How to manage a 16-year-old patient with abdominal pain, fever, lower back pain, and a complete blood count (CBC) showing a normal leukocyte count with a differential count of lymphocytes 0.20, monocytes 0.15, and eosinophils 0.01?

Management of a 16-Year-Old with Abdominal Pain, Fever, and Lower Back Pain

Immediate Diagnostic Imaging Required

This clinical presentation—abdominal pain, fever, and lower back pain in an adolescent—requires urgent CT imaging of the abdomen and pelvis with IV contrast to rule out complicated appendicitis, abscess formation, or other surgical emergencies. 1

The combination of fever with abdominal pain represents a potential surgical emergency and indicates appendicitis until proven otherwise. 2 The addition of lower back pain raises concern for retroperitoneal involvement, perforation, or abscess formation. 3

Key Clinical Considerations

CBC Interpretation

• The leukocyte count of 6 (normal) does NOT exclude serious pathology. 1
• The differential showing lymphocyte 0.20 (20%), monocyte 0.15 (15%), and eosinophil 0.01 (1%) suggests a relative lymphopenia and possible early bacterial infection
• Approximately 50% of patients with appendicitis do NOT present with leukocytosis 1
• Normal white blood cell counts can occur despite serious infection, particularly in adolescents 1

Why CT is Essential

• CT abdomen/pelvis with IV contrast has 85.7-100% sensitivity and 94.8-100% specificity for appendicitis 1
• CT is critical for detecting complications including abscess (>3 cm), perforation, or retroperitoneal involvement 1
• The lower back pain component suggests possible retroperitoneal extension, which CT will definitively identify 3
• CT without oral contrast is acceptable and avoids treatment delays 1

Immediate Management Steps

1. Obtain CT Abdomen/Pelvis with IV Contrast Immediately

• Do not delay for oral contrast administration 1
• Evaluate for appendicitis, abscess formation, perforation, diverticulitis, or other intra-abdominal pathology 1

2. Start Broad-Spectrum Antibiotics Empirically

• Begin antibiotics immediately if the patient appears clinically unstable or has peritoneal signs 2
• Appropriate regimens include: piperacillin-tazobactam, ertapenem, or cefotaxime/ceftriaxone plus metronidazole 2
• Third-generation cephalosporins (cefotaxime 2g IV q8h) are first-line for suspected intra-abdominal infection 1

3. Obtain Immediate Surgical Consultation

• Required when imaging confirms complicated infection or abscess formation 2
• Antibiotics alone are insufficient for perforated appendicitis 2

Differential Diagnosis to Consider

High-Priority Diagnoses

• Complicated appendicitis with perforation/abscess (most likely given fever + abdominal pain + back pain) 1, 2
• Diverticulitis with retroperitoneal perforation (can present with back pain and fever) 3
• Pyelonephritis or perinephric abscess (explains back pain component) 1
• Liver abscess (can present with RUQ pain, fever, and referred back pain) 4

Alternative Considerations

• Streptococcal pharyngitis (causes abdominal pain in 27% of children—perform rapid strep test if sore throat present) 2
• Inflammatory bowel disease (less likely with acute presentation) 1
• Ovarian pathology in females (tubo-ovarian abscess) 1

Clinical Pitfalls to Avoid

• Do NOT rely on normal leukocyte count to exclude serious pathology 1
• Do NOT delay imaging in favor of observation when fever and abdominal pain coexist 1
• Do NOT assume viral etiology without imaging confirmation 1
• Do NOT miss retroperitoneal pathology by focusing only on intraperitoneal causes 3

If CT Shows Abscess >3 cm

• Percutaneous catheter drainage (PCD) plus antibiotics is the preferred initial approach 1
• PCD has 70-90% efficacy and shorter hospital stays compared to immediate surgery 1
• Interval appendectomy may be considered after successful drainage 1
• For collections adjacent to the cecum with appendicolith, PCD followed by delayed surgery or PCD alone are both appropriate 1

Follow-Up Imaging Considerations

• If CT is negative but symptoms persist, consider MRI without/with IV contrast (sensitivity 86-94%, specificity 94%) 2
• Ultrasound is operator-dependent and less useful when CT is available, but can be considered for hepatic or renal pathology 4