French researchers reviewed 16 studies investigating clinical decision rules for predicting group A streptococcal pharyngitis in a paediatric population, to identify any rules that are no worse than rapid diagnostic tests in identifying children with pharyngitis. The researchers aimed to use the rules to identify children at low risk of pharyngitis, so avoiding antibiotic treatment. Criteria for evaluation of the rules was a standard error as good as that of rapid diagnostic tests, and a probability of group A streptococcal pharyngitis of below 11% in the low-risk group of children. This probability corresponds to a negative likelihood ratio of 0.2 or less, with literature deeming this as ‘clinically useful’.
Only one rule, developed by Joachim et al., was deemed potentially useful for clinical practice. It had a negative likelihood ratio of 0.3, and application of this rule brought the probability of group A streptococcal pharyngitis down from 34% to 13%. The rule led to a 3.6% false-negative rate in the low-risk population.
What does it mean for GPs?
The authors concluded that their analyses ‘confirmed that symptoms alone were not sufficient to rule out diagnosis’ of group A streptococcal pharyngitis. The rule from Joachim et al. ‘performed the best but has not been externally validated and requires the collection of nine variables for its application, which may limit its use in practice.’