A Zar score ≥ 2 was originally used to justify the choice of Vancomycin over Metronidazole in early CDI guidelines.
Guidelines & Evidence
Clinical Details
Section 1
When to Use
When to Use
Prognostic stratification of patients with *Clostridioides difficile* infection (CDI)
To identify patients who require "Severe" treatment regimens (Oral Vancomycin/Fidaxomicin over Metronidazole)
Standardized clinical assessment for initial management in the inpatient setting
Philosophy of Zar
The Zar score is designed to identify "Severe" disease, which carries a much higher risk of treatment failure with Metronidazole.
Section 2
Formula & Logic
The 6 Severity Item (1 pt each)
Age > 60 years.
Temperature > 38.3 °C (101 °F).
Albumin < 2.5 mg/dL.
WBC > 15,000 cells/mm³.
Endoscopic evidence (Pseudomembranes).
Admitted to the ICU.
Risk Grouping
0–1 Points
Mild-to-Moderate Disease
≥ 2 Points
Severe Disease
Section 3
Pearls/Pitfalls
Metronidazole vs. Vancomycin
The Zar score was the central tool in the landmark trial that proved Oral Vancomycin was superior to Metronidazole in "Severe" CDI. In the Severe group, Vancomycin achieved a cure rate of 97% compared to only 76% for Metronidazole.
The Albumin Marker
Hypoalbuminemia ($<2.5$) in CDI is a marker of severe "protein-losing enteropathy" caused by the TcdA and TcdB toxins. This state indicates significant mucosal integrity failure and high risk of systemic toxic shock.
Clinical Pearls
Presence of pseudomembranes on sigmoidoscopy is 100% pathognomonic for severe disease
The threshold for severe disease (Score ≥ 2) has a sensitivity of ~80% for predicting treatment failure
In modern IDSA 2021 guidelines, Vancomycin or Fidaxomicin is now often the first choice for all categories, but Zar remains a valuable tool for risk-stratifying those who need intensive monitoring
Developed by Dr. Fred Zar and his team at the University of Illinois at Chicago. At the time of publication, many clinicians believed Vancomycin was unnecessary; Zar's study provided the objective proof that patient severity should dictate drug choice.
