What laboratory tests and medications are recommended for a patient suspected of having appendicitis?

Laboratory Tests and Medications for Suspected Appendicitis

For patients with suspected appendicitis, white blood cell count (WBC) and C-reactive protein (CRP) are the most important laboratory tests, while broad-spectrum antibiotics such as piperacillin-tazobactam are recommended for treatment once the diagnosis is confirmed. 1

Laboratory Tests

Primary Laboratory Tests

• White Blood Cell Count (WBC):

  • Elevated WBC (>10,000/mm³) has a positive likelihood ratio of 2.47 for appendicitis 1
  • Higher WBC (>15,000/mm³) increases positive likelihood ratio to 3.47 1
  • Alone, WBC has limited specificity but is a useful screening tool 1

• C-reactive Protein (CRP):

  • CRP level ≥10 mg/L has a positive likelihood ratio of 4.24 for acute appendicitis 1
  • Strong predictor in children, with CRP ≥10 mg/L being highly suggestive 1

• Combined WBC and CRP:

  • The combination of WBC >10,000/mm³ and CRP >8 mg/L has:
    • Positive likelihood ratio of 23.32 (highly predictive of appendicitis)
    • Negative likelihood ratio of 0.03 (excellent for ruling out appendicitis) 1
  • This combination is significantly more useful than either test alone 1

Additional Laboratory Tests

• Absolute Neutrophil Count (ANC):

  • Elevated neutrophil count and neutrophilia (>75%) are sensitive markers 1, 2
  • Particularly useful in pediatric patients 1

• Urinalysis:

  • Recommended to exclude urinary tract pathology that may mimic appendicitis 3

Risk Stratification Using Clinical Scores

• Alvarado Score: Combines symptoms, physical findings, and laboratory values (WBC count and neutrophilia) 1, 3

  • Score ≤3: Low risk (5% chance of appendicitis)
  • Score 4-6: Intermediate risk (36% chance of appendicitis)
  • Score ≥7: High risk (78% chance of appendicitis) 1

• Appendicitis Inflammatory Response (AIR) Score: Incorporates CRP and has higher discriminating power than Alvarado score in adults 1, 3

• Pediatric Appendicitis Score (PAS): Useful tool for excluding appendicitis in children 1, 3

Medication Recommendations

Antibiotic Therapy

Once appendicitis is diagnosed or strongly suspected, antibiotic therapy should be initiated:

1. First-line antibiotics for adults:

   • Piperacillin-tazobactam: 3.375g IV every 6 hours 4, 5
   • For pediatric patients with appendicitis/peritonitis:
     • 2 months to 9 months: 90 mg/kg every 8 hours
     • Older than 9 months: 112.5 mg/kg every 8 hours 4

2. Alternative regimens:

   • Cephalosporins (third-generation) plus metronidazole 5
   • Fluoroquinolones plus metronidazole 5

Antibiotic Considerations

• Antibiotic coverage should target common organisms in appendicitis:

  • Escherichia coli (present in 85% of cases)
  • Klebsiella pneumoniae (26%)
  • Streptococcus species (25%)
  • Enterococcus species (18%)
  • Pseudomonas aeruginosa (15%) 6

• Pseudomonas aeruginosa has been associated with surgical site infections and should be covered by the selected antibiotic regimen 6

Common Pitfalls to Avoid

1. Relying on a single laboratory test: Neither WBC nor CRP alone is sufficiently sensitive or specific for diagnosing appendicitis 1

2. Delaying antibiotics: Prompt administration of antibiotics is essential once appendicitis is diagnosed to prevent progression to perforation 1

3. Overlooking special populations:

   • Pregnant patients require special consideration with modified laboratory thresholds 1
   • Immunosuppressed patients may have atypical presentations 7

4. Misinterpreting normal laboratory values: Laboratory tests may be normal in early appendicitis; clinical suspicion should guide further evaluation 1

5. Failing to reassess: If initial tests are negative but clinical suspicion remains high, repeat laboratory tests and imaging should be considered 3

By combining clinical assessment, laboratory testing, and appropriate imaging, the diagnosis of appendicitis can be made with high accuracy, allowing for timely intervention and improved patient outcomes.