Sore Throat in the Clinic: Centor Scoring, When to Test for Strep and What to Prescribe
Use the Centor or McIsaac score to decide who needs testing: patients with clear viral features or a score of 0 to 1 need neither a test nor antibiotics, and those with higher scores get a rapid strep test, with a backup culture after a negative rapid test in children and adolescents but not routinely in adults. Antibiotics are given only for confirmed group A streptococcal pharyngitis. Penicillin V or amoxicillin for 10 days is first line under the IDSA 2012 guideline, with cephalexin, cefadroxil, clindamycin, azithromycin or clarithromycin for penicillin allergy.
Most sore throats are viral, and the provider's job is to find the minority that are group A streptococcal (GAS) without testing or treating everyone. Score the patient with Centor or McIsaac criteria: clear viral features or a score of 0 to 1 means no test and no antibiotic, while higher scores mean a rapid antigen detection test (RADT), with a backup throat culture after a negative RADT in children and adolescents but not routinely in adults. Only confirmed GAS pharyngitis is treated, and under the IDSA 2012 guideline the first-line drugs are penicillin V or amoxicillin for 10 days, with specific alternatives for penicillin allergy.
Assessment: history and examination
Start by asking what makes strep unlikely. IDSA 2012 advises against testing patients whose presentation strongly suggests a viral cause: cough, rhinorrhea, hoarseness, conjunctivitis, oral ulcers or diarrhea. Features that make GAS more likely are sudden-onset sore throat, fever, tonsillar exudate or swelling, tender anterior cervical nodes, palatal petechiae, scarlatiniform rash, and age 5 to 15 years, often with headache, abdominal pain, nausea or vomiting in children.
Also look for the conditions that look like strep but change management:
- Infectious mononucleosis: exudative tonsillitis with posterior cervical adenopathy, marked fatigue, splenomegaly and atypical lymphocytes. A heterophile antibody test helps; amoxicillin causes a rash in many patients.
- Acute HIV infection: pharyngitis with fever, rash and lymphadenopathy after a recent exposure.
- Gonococcal pharyngitis: consider after oral sexual exposure; it needs a nucleic acid test, not a strep test.
- Peritonsillar abscess, retropharyngeal abscess, epiglottitis and Lemierre syndrome (see red flags below).
IDSA 2012 also advises against routine testing in children under 3 years, because GAS pharyngitis and rheumatic fever are uncommon in that age group, unless risk factors such as an older sibling with GAS infection are present.
Centor and McIsaac scores with cut-offs
The original Centor score was derived in adults in an emergency department. McIsaac added an age adjustment so the score can be used in children and older adults.
| Criterion | Points |
|---|---|
| Temperature above 38 C (history or measured) | 1 |
| Absence of cough | 1 |
| Tender, swollen anterior cervical lymph nodes | 1 |
| Tonsillar swelling or exudate | 1 |
| Age 3 to 14 years (McIsaac only) | 1 |
| Age 15 to 44 years (McIsaac only) | 0 |
| Age 45 years or older (McIsaac only) | Minus 1 |
The way scores are used in primary care differs from how they were first proposed. McIsaac's original strategy treated high scores empirically; IDSA 2012 and the ACP/CDC high-value care advice instead require microbiologic confirmation before antibiotics.
| Score | Approach consistent with IDSA 2012 and ACP/CDC |
|---|---|
| 0 to 1, or obvious viral features | No testing, no antibiotics; symptomatic care |
| 2 to 3 | RADT; treat if positive; backup culture if negative in a child or adolescent |
| 4 or more | RADT (or culture); treat if positive; empiric treatment on the score alone is not recommended by IDSA |
The score is a filter for testing, not a diagnosis. A high score still carries a meaningful chance of viral illness, and a positive test in a patient with a viral picture may reflect carriage.
Testing rules
- RADT is the first test. A positive RADT does not need confirmation by culture.
- Negative RADT in a child or adolescent: send a throat culture. Negative RADT in an adult: culture is not routinely needed.
- Swab both tonsils or tonsillar fossae and the posterior pharyngeal wall, not the tongue or cheek.
- Antistreptococcal antibody titers (ASO, anti-DNase B) reflect past infection and play no role in diagnosing acute pharyngitis.
- Do not test asymptomatic household contacts, and do not perform a test of cure after treatment in a patient whose symptoms have resolved.
- Chronic GAS carriers do not usually need antibiotics; a carrier with a viral illness can test positive, which is one reason viral features argue against testing.
Treatment: IDSA 2012 regimens
Treatment shortens symptoms modestly, reduces transmission and suppurative complications, and prevents acute rheumatic fever when started within about nine days of symptom onset, so a short wait for a culture result is safe.
| Patient | Regimen | Duration |
|---|---|---|
| No penicillin allergy, child | Penicillin V 250 mg twice or three times daily | 10 days |
| No penicillin allergy, adolescent or adult | Penicillin V 250 mg four times daily or 500 mg twice daily | 10 days |
| No penicillin allergy, any age | Amoxicillin 50 mg/kg once daily (maximum 1,000 mg) or 25 mg/kg twice daily (maximum 500 mg per dose) | 10 days |
| Adherence concern | Benzathine penicillin G intramuscular: 600,000 units if under 27 kg, 1,200,000 units if 27 kg or more | Single dose |
| Penicillin allergy, not anaphylactic | Cephalexin 20 mg/kg per dose twice daily (maximum 500 mg per dose) or cefadroxil 30 mg/kg once daily (maximum 1 g) | 10 days |
| Penicillin allergy, anaphylactic or immediate type | Clindamycin 7 mg/kg per dose three times daily (maximum 300 mg per dose) | 10 days |
| Penicillin allergy, anaphylactic or immediate type | Azithromycin 12 mg/kg once daily (maximum 500 mg) | 5 days |
| Penicillin allergy, anaphylactic or immediate type | Clarithromycin 7.5 mg/kg per dose twice daily (maximum 250 mg per dose) | 10 days |
Notes that drive exam answers:
- No GAS isolate has ever been resistant to penicillin, which is why a narrow-spectrum penicillin remains first line. Macrolide and clindamycin resistance does occur, which is why they are reserved for allergy.
- First-generation cephalosporins are avoided in patients with an immediate (anaphylactic) penicillin reaction.
- Azithromycin is the only regimen shorter than 10 days because of its long tissue half-life.
- Adjunctive therapy: acetaminophen or an NSAID for pain and fever. Avoid aspirin in children because of Reye syndrome. IDSA 2012 recommends against adjunctive corticosteroids.
Recurrent episodes and tonsillectomy
A patient with repeated positive tests may be a chronic carrier who keeps catching viral infections, rather than someone with true recurrent GAS pharyngitis. IDSA 2012 suggests distinguishing the two before escalating therapy, and recommends against tonsillectomy solely to reduce the frequency of GAS pharyngitis. Referral to otolaryngology follows the frequency criteria in the current tonsillectomy guideline; confirm the thresholds there.
Monitoring and follow-up
- Expect clear improvement within 24 to 72 hours of antibiotics. No routine follow-up visit or repeat test is needed when symptoms resolve.
- Re-evaluate if symptoms persist beyond about 72 hours, worsen, or return after an initial response: consider an abscess, mononucleosis, a different diagnosis, or nonadherence.
- Watch for nonsuppurative complications in the weeks after infection: acute rheumatic fever (carditis, arthritis, chorea, erythema marginatum, subcutaneous nodules) and post-streptococcal glomerulonephritis (cola-colored urine, edema, hypertension), which antibiotics do not prevent.
Red flags: emergency referral or admission
| Finding | Concern |
|---|---|
| Trismus, muffled "hot potato" voice, uvular deviation, unilateral peritonsillar bulge | Peritonsillar abscess |
| Drooling, stridor, tripod posture, toxic appearance, severe pain with a near-normal pharynx | Epiglottitis |
| Neck stiffness or pain on neck extension, fever, dysphagia in a young child | Retropharyngeal abscess |
| Persistent fever, unilateral neck swelling along the jugular vein, septic lung emboli in an adolescent or young adult | Lemierre syndrome |
| Inability to swallow fluids, dehydration, respiratory distress | Admission regardless of cause |
Patient and family education
- Take the full 10-day course (5 days for azithromycin) even when the throat feels better in a day or two, because the course length is what prevents rheumatic fever.
- Stay home from school or work until fever-free and at least 12 to 24 hours after starting antibiotics, per CDC.
- Replace shared utensils and do not share drinks; hand hygiene limits spread in households.
- Return for drooling, difficulty breathing, inability to swallow, a muffled voice, or symptoms lasting more than 72 hours on treatment.
- For a negative test: explain why antibiotics will not help a viral sore throat and offer symptom control.
- For mononucleosis: avoid contact sports while the spleen may be enlarged; confirm the return-to-play interval with current guidance.
How the exam tests this
- Treating on the score alone. A 20-year-old with a Centor score of 4 is tested, not given empiric amoxicillin, under IDSA 2012.
- Backup culture in adults. A negative RADT in an adult does not require a culture; in a child it does.
- The viral picture. Cough, rhinorrhea and hoarseness mean no test and no antibiotic, even with fever.
- Mononucleosis traps: posterior nodes, splenomegaly and fatigue, and the amoxicillin rash.
- Azithromycin as first line. It is an allergy alternative only.
- Cephalexin for anaphylactic penicillin allergy. Wrong; use clindamycin or a macrolide.
- Test of cure or testing household contacts. Not recommended.
- Missing the abscess. Trismus and uvular deviation change the answer to same-day emergency referral.
Practice question
A 16-year-old girl has had a sore throat and fever to 38.5 C for two days. She has no cough or nasal congestion. Examination shows tonsillar exudate and tender anterior cervical lymph nodes, no posterior adenopathy and no splenomegaly. She has no drug allergies. A rapid antigen detection test is negative. Which of the following is the most appropriate next step?
- A. Prescribe amoxicillin 50 mg/kg once daily (maximum 1,000 mg) for 10 days.
- B. Send a throat culture and treat only if it is positive.
- C. Reassure her that a negative rapid test rules out strep and recommend symptomatic care only.
- D. Order an antistreptolysin O titer.
Answer: B. Her McIsaac score is 4 (fever, no cough, exudate, tender anterior nodes, age 15 to 44 adds nothing), which justifies testing, and IDSA 2012 recommends a backup throat culture after a negative RADT in children and adolescents. Option A treats empirically on clinical grounds, which the guideline does not support without a positive test. Option C would be acceptable for an adult, but in an adolescent a negative RADT is not sensitive enough to stop there. Option D measures antibodies that reflect past infection and has no role in diagnosing acute pharyngitis.
Key points
- Do not test patients with clear viral features (cough, rhinorrhea, hoarseness, oral ulcers) or a Centor or McIsaac score of 0 to 1.
- Centor points: fever above 38 C, no cough, tender anterior nodes, tonsillar exudate or swelling; McIsaac adds 1 for ages 3 to 14 and subtracts 1 for 45 and older.
- Treat only confirmed GAS pharyngitis; a positive RADT needs no culture confirmation.
- Back up a negative RADT with culture in children and adolescents, not routinely in adults.
- First line: penicillin V or amoxicillin for 10 days, or one dose of IM benzathine penicillin G.
- Penicillin allergy: cephalexin or cefadroxil if not anaphylactic; clindamycin, azithromycin (5 days) or clarithromycin if anaphylactic.
- Trismus, uvular deviation, drooling or stridor means emergency referral.
Related NPPace guides
- UTI Antibiotic Choices and Durations: Cystitis, Pyelonephritis, Men, Pregnancy and Recurrence
- Asthma Step Therapy on the NP Exam: GINA Tracks, Stepping Up and Stepping Down
- COPD in Primary Care: GOLD Groups, Inhaler Choice and When to Add What
- How to Read a Primary-Care Vignette Like a Provider: The 5-Step Method
- AANP vs ANCC: Which NP Certification Exam Should You Take?
Frequently asked questions
Common follow-up questions on Respiratory & Infectious Disease.
Can strep pharyngitis be diagnosed on clinical findings alone?
No. IDSA 2012 states that clinical features cannot reliably distinguish streptococcal from viral pharyngitis, so a rapid antigen test or culture is needed before antibiotics. Scores decide who is worth testing.
Does an adult with a negative rapid strep test need a throat culture?
Not routinely. Backup culture is recommended for children and adolescents because of their higher rate of group A strep and risk of rheumatic fever; adults have a lower incidence and very low rheumatic fever risk.
Why is amoxicillin a problem in a teenager with exudative pharyngitis?
Infectious mononucleosis mimics strep throat, and amoxicillin given during Epstein-Barr virus infection often causes a widespread rash. Posterior cervical nodes, marked fatigue and splenomegaly point toward mononucleosis.
When can a child with strep throat return to school?
CDC advises staying home until afebrile and at least 12 to 24 hours after starting an appropriate antibiotic, with 24 hours considered in settings such as outbreaks or healthcare work.
Sources and references
- Shulman ST, Bisno AL, Clegg HW, et al. Clinical Practice Guideline for the Diagnosis and Management of Group A Streptococcal Pharyngitis: 2012 Update by the Infectious Diseases Society of America. Clinical Infectious Diseases. 2012. https://doi.org/10.1093/cid/cis629
- Centor RM, Witherspoon JM, Dalton HP, Brody CE, Link K. The diagnosis of strep throat in adults in the emergency room. Medical Decision Making. 1981. https://doi.org/10.1177/0272989X8100100304
- McIsaac WJ, Kellner JD, Aufricht P, Vanjaka A, Low DE. Empirical validation of guidelines for the management of pharyngitis in children and adults. JAMA. 2004. https://doi.org/10.1001/jama.291.13.1587
- Harris AM, Hicks LA, Qaseem A. Appropriate Antibiotic Use for Acute Respiratory Tract Infection in Adults: Advice for High-Value Care From the American College of Physicians and the Centers for Disease Control and Prevention. Annals of Internal Medicine. 2016. https://doi.org/10.7326/M15-1840
- Centers for Disease Control and Prevention. Clinical Guidance for Group A Streptococcal Pharyngitis. CDC. 2025. https://www.cdc.gov/group-a-strep/hcp/clinical-guidance/strep-throat.html
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