Classifying the diagnosis of acute rheumatic fever

A diagnosis of acute rheumatic fever can be classified as definite, probable or possible, depending on the significance and number of clinical manifestations present (see Major and minor manifestations for the diagnosis of acute rheumatic fever), and whether there is evidence of preceding S. pyogenes infection. This classification indicates the certainty of the diagnosis, and has implications for long-term management and follow-up, including the duration of secondary prophylaxis against S. pyogenes infection. Do not discount the possibility of acute rheumatic fever in patients who do not meet the diagnostic criteria, particularly if acute investigations are incomplete or delayed.

Preceding S. pyogenes infection can be demonstrated byRHDAustralia (ARF/RHD writing group), 2020:

• elevated or rising antibody titre (commonly antistreptolysin O or antiDNase B)
• detection of S. pyogenes on throat culture
• detection of S. pyogenes by rapid antigen or nucleic acid amplification test on throat swab.

A definite diagnosis of acute rheumatic fever is specified asRHDAustralia (ARF/RHD writing group), 2020:

• initial episode
  • the presence of 2 major manifestations plus evidence of preceding S. pyogenes infection, or
  • the presence of 1 major and 2 minor manifestations plus evidence of preceding S. pyogenes infection
• recurrent episode (patient has a documented history of acute rheumatic fever or rheumatic heart disease)
  • the presence of 2 major manifestations plus evidence of preceding S. pyogenes infection, or
  • the presence of 1 major and 2 minor manifestations plus evidence of preceding S. pyogenes infection, or
  • the presence of 3 minor manifestations plus evidence of preceding S. pyogenes infection.

Patients may be classified as having probable or possible acute rheumatic fever (either an initial or recurrent episode) if acute rheumatic fever is suspected, but the criteria for a definite episode are not met because the patient falls short by one major or one minor criterion, or the patient does not have evidence of preceding S. pyogenes infection, including when streptococcal serology is not available or is within normal limits.

A diagnosis of probable acute rheumatic fever is made when acute rheumatic fever is considered the most likely diagnosis; a diagnosis of possible acute rheumatic fever is made when acute rheumatic fever is considered less likely than other diagnoses, but cannot be excluded. As this can be a difficult clinical decision, consult with a paediatrician or other specialist with expertise in acute rheumatic feverRHDAustralia (ARF/RHD writing group), 2020.