Relationship Between UTI and Alvarado Score in Appendicitis Diagnosis
Urinary tract infection (UTI) is not a component of the Alvarado score, and its presence can confound the diagnosis of acute appendicitis by mimicking or masking symptoms. 1
The Alvarado Score Components
The Alvarado score is a clinical scoring system used to stratify the risk of appendicitis in patients with abdominal pain. It includes the following components:
- Migration of pain to right lower quadrant (1 point) 1
- Anorexia (1 point) 1
- Nausea/vomiting (1 point) 1
- Tenderness in right lower quadrant (2 points) 1
- Rebound pain (1 point) 1
- Elevated temperature (1 point) 1
- Leukocytosis >10,000/mm³ (2 points) 1
- Shift to the left of neutrophils >75% (1 point) 1
UTI as a Confounding Factor
UTI can affect the Alvarado score and appendicitis diagnosis in several ways:
- Symptom overlap: UTI can cause abdominal pain, particularly in the lower abdomen, which may mimic appendicitis pain 2, 3
- Leukocytosis: Both UTI and appendicitis can cause elevated white blood cell count, potentially leading to a falsely elevated Alvarado score 1, 4
- Pyuria: The presence of UTI can lead to pyuria (white blood cells in urine), which is not accounted for in the Alvarado score but may confuse the clinical picture 3
- Fever: Both conditions can present with fever, contributing to potential diagnostic confusion 4, 2
Diagnostic Implications
- False positives: Patients with UTI may have an elevated Alvarado score (≥7) without having appendicitis, leading to unnecessary imaging or even surgery 5
- Diagnostic challenges: The 2020 WSES guidelines acknowledge that establishing the diagnosis of acute appendicitis based solely on clinical presentation and physical examination may be challenging, requiring a tailored individualized approach 1
- Reduced specificity: The presence of UTI may reduce the specificity of the Alvarado score, which is already considered insufficiently specific for diagnosing acute appendicitis in adults 1
Clinical Approach When UTI is Suspected
When evaluating a patient with suspected appendicitis and possible UTI:
- Consider both diagnoses: Both conditions can coexist, and the presence of one does not exclude the other 4, 3
- Urinalysis: Perform urinalysis to evaluate for UTI in patients with suspected appendicitis, especially when symptoms are atypical 2
- Additional imaging: In patients with intermediate Alvarado scores (4-6) and symptoms suggestive of UTI, consider imaging to help differentiate between diagnoses 1
- Alternative scoring systems: Consider using the AIR (Appendicitis Inflammatory Response) score or AAS (Adult Appendicitis Score) which may have better discriminating power than the Alvarado score 1
Recommendations for Clinical Practice
- Do not rely solely on Alvarado score: The 2020 WSES guidelines suggest against using the Alvarado score alone to positively confirm clinical suspicion of acute appendicitis in adults 1
- Consider UTI in differential diagnosis: Always include UTI in the differential diagnosis of abdominal pain, especially in female patients 4, 3
- Use appropriate imaging: For patients with suspected appendicitis and possible UTI, ultrasound or CT scan should be considered based on the patient's age and risk factors 1
- Laboratory testing: Include urinalysis and urine culture when evaluating patients with suspected appendicitis, particularly when symptoms are atypical or the Alvarado score is in the intermediate range 2, 3
Special Considerations
- Elderly patients: In elderly patients, both UTI and appendicitis can present atypically, making the Alvarado score less reliable 1
- Pregnant patients: The WSES guidelines specifically recommend against making the diagnosis of acute appendicitis in pregnant patients based on symptoms and signs only; laboratory tests and inflammatory parameters should always be requested 1
- Pediatric patients: In children, the Alvarado score and Pediatric Appendicitis Score may have limitations, and UTI should be considered in the differential diagnosis 1