Blood tests, including inflammatory markers, are not useful in differentiating bacterial from viral pharyngitis because they can also be increased in some viral infections. Antistreptolysin O titer and anti-DNAse antibodies are useful for the diagnosis of poststreptococcal complications, such as rheumatic fever and glomerularnephritis, both occurring some weeks after the acute streptococcal infection. They are not of help for the diagnosis at the time of an episode of acute pharyngitis.