Centor Criteria Calculator for Strep Pharyngitis (Modified/McIsaac)

What is Centor Criteria (Modified)?

The Modified Centor Criteria, also known as the McIsaac Criteria, are used to evaluate the likelihood of Group A Streptococcal (GAS) pharyngitis in patients presenting with a sore throat, adjusting for age.

Here’s the detailed breakdown:

Modified Centor (McIsaac) Criteria Components:

• Presence of tonsillar exudates
• Tender or swollen anterior cervical lymph nodes
• Fever over 38°C (100.4°F)
• Absence of cough

Age adjustment:

• Add 1 point if the patient is aged 3 to 14 years.
• No additional points for patients aged 15 to 44 years.
• Subtract 1 point for patients aged 45 years and older.

Scoring and Recommendations:

• Score -1, 0: GAS pharyngitis unlikely. No antibiotics or further testing recommended.
• Score 1, 2: Moderate likelihood of GAS. Consider a rapid antigen detection test (RADT). Treat with antibiotics only if RADT is positive.
• Score 3, 4, 5: High likelihood of GAS. Empiric antibiotic therapy may be warranted, or confirmatory testing with RADT or throat culture can be considered based on clinical judgment.

Interpretation with Scores:

• Score -1 or 0: The risk of GAS infection is very low, and management typically does not include antibiotics.
• Score 1–2: There is a moderate risk of GAS infection; decision for further testing like RADT is guided by clinical judgment.
• Score 3–5: Suggests a high risk of GAS infection, and initiating antibiotics may be appropriate, or one might opt for confirmatory testing if needed.

These criteria help clinicians decide when it is appropriate to perform further testing for strep throat or when to start or avoid antibiotics, thus contributing to more accurate diagnosis and treatment, reducing unnecessary antibiotic use, and addressing public health concerns about antibiotic resistance.

References

• Centor RM, Witherspoon JM, Dalton HP, Brody CE, Link K. The diagnosis of strep throat in adults in the emergency room. Med Decis Making. 1981;1(3):239-46. doi: 10.1177/0272989X8100100304. PMID: 6763125.
• McIsaac WJ, White D, Tannenbaum D, Low DE. A clinical score to reduce unnecessary antibiotic use in patients with sore throat. CMAJ. 1998 Jan 13;158(1):75-83. PMID: 9475915; PMCID: PMC1228750.