Acute Rheumatic Fever (ARF): High ASO (Antistreptolysin O) titre indicates a recent streptococcal infection, which is a precursor to ARF. Elevated CRP (C-reactive protein) suggests an ongoing inflammatory process, consistent with ARF.

Poststreptococcal Glomerulonephritis (PSGN): Following a streptococcal infection, PSGN can occur, leading to kidney inflammation. High ASO titre and elevated CRP are consistent with this diagnosis.
Streptococcal Pharyngitis: Although the ASO titre can remain elevated for weeks after the infection, a high CRP suggests an active infection or a recent infection with ongoing inflammation.
Autoimmune Disorders (e.g., Rheumatoid Arthritis): While less directly linked to high ASO titres, autoimmune disorders can cause elevated CRP and may occasionally have a high ASO titre due to cross-reactivity or concurrent infections.

Endocarditis: Although less common, endocarditis is a serious condition that can follow streptococcal infections. High ASO titre and elevated CRP, along with other symptoms like fever and heart murmurs, necessitate consideration of this diagnosis.
Septic Arthritis: A bacterial infection of the joint, which can be caused by streptococcal species. The combination of high ASO titre and elevated CRP, especially with joint symptoms, should prompt consideration of septic arthritis.

Sydenham's Chorea: A rare manifestation of ARF, characterized by neurological symptoms. While the high ASO titre supports this diagnosis, it is less common and typically presents with distinct neurological findings.
Streptococcal Toxic Shock Syndrome (STSS): A severe condition with high mortality, characterized by shock and multi-organ failure following a streptococcal infection. Although rare, the combination of high ASO titre and significantly elevated CRP, along with signs of shock, should raise suspicion for STSS.