Probability of Strep Pharyngitis
Total Score
Strep likelihood 1-10%. No further testing or antibiotics needed.
Disclaimer: The clinical scoring and algorithms on this platform are intended strictly for professional informational purposes. They do not constitute a definitive medical diagnosis, treatment, or clinical decision. The final judgment and responsibility lie with the treating physician.
Yasal Uyarı: Bu platformdaki klinik skorlamalar ve algoritmalar yalnızca sağlık profesyonellerini bilgilendirme amaçlıdır. Herhangi bir kesin tıbbi teşhis, tedavi veya klinik karar yerine geçemez. Nihai karar ve sorumluluk hastayı yatak başında değerlendiren hekime aittir.
The Modified Centor Score (McIsaac score) estimates the probability that pharyngitis is caused by Group A Streptococcus (GAS). By evaluating fever, tonsillar exudates, cervical lymphadenopathy, absence of cough, and patient age, it rationalizes the use of rapid antigen detection testing (RADT) and limits inappropriate empirical antibiotic prescriptions for viral sore throats.
The most critical prerequisite for using this score is that the patient must lack obvious viral symptoms. If the patient has rhinorrhea, conjunctivitis, or a prominent cough, the etiology is almost certainly viral, and the Centor score should not be applied.
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):239-246.
McIsaac WJ, White D, Tannenbaum D, Low DE. A clinical score to reduce unnecessary antibiotic use in patients with sore throat. CMAJ. 1998;158(1):75-83.
Disclaimer: The clinical scoring and algorithms on this platform are intended strictly for professional informational purposes. They do not constitute a definitive medical diagnosis, treatment, or clinical decision. The final judgment and responsibility lie with the treating physician.
Apply the Modified Centor (McIsaac) Score to patients ≥ 3 years old presenting with acute sore throat to guide decisions on Rapid Antigen Detection Test (RADT) and antibiotic prescribing. Score ≤ 1: no testing, no antibiotics, viral aetiology very likely. Score 2–3: perform a RADT; treat with antibiotics only if positive. Score ≥ 4: RADT or empiric antibiotics are both acceptable — treat with penicillin V (or amoxicillin) as first-line if group A Streptococcus (GAS) is being treated. Do NOT apply this score if the patient has features of peritonsillar abscess, epiglottitis, or Ludwig's angina.
The 'absence of cough' criterion is counterintuitive but clinically powerful — cough strongly suggests viral aetiology (rhinovirus, coronavirus, adenovirus). Exudates alone are not diagnostic for GAS: infectious mononucleosis (EBV) can produce profuse tonsil exudate and lymphadenopathy with a Centor score ≥ 4. In adolescents and young adults, always consider a monospot test or EBV serology before initiating amoxicillin — the ampicillin rash in EBV is a widely recognized pitfall.
GAS pharyngitis is self-limiting in the vast majority of cases; the primary goal of antibiotic treatment is prevention of acute rheumatic fever (ARF) — most relevant in children and lower-income populations with higher ARF prevalence. In adults at low ARF risk, the net benefit of antibiotics for mild pharyngitis is marginal. The score was validated on adult populations; sensitivity and specificity differ in children. The original Centor criteria did not include age; the McIsaac modification (adding age adjustment) improved specificity in adults but age weighting should be applied correctly — age ≥ 45 subtracts 1 point.
McIsaac WJ, White D, Tannenbaum D, Low DE. A clinical score to reduce unnecessary antibiotic use in patients with sore throat. Canadian Medical Association Journal. 1998;158:75–83.