Results from antibiotic susceptibility testing can be quantitatively compared with reference results to determine their essential agreement. This can help determine if the susceptibility testing is accurate and reliable.
Requirement: serial dilution with 4 or more consecutive 2-fold dilutions
A test result is in essential agreement with the reference result if it:
(1) has the same value as the reference result (exact agreement)
(2) it is one dilution higher than the reference result
(3) it is one dilution lower than the reference result
A test result is not in essential agreement with the reference result if it:
(1) it is 2 or more dilutions higher (more dilute) than the reference result
(2) it is 2 or more dilutions lower (more concentrated) than the reference result
percent essential agreement =
= (number of tests with essential agreement) / (number of tests performed)
percent exact agreement =
= (number of tests with the same result) / (number of tests performed)
These can be calculated for:
(1) all organisms and all antibiotics
(2) all organisms for a given antibiotic
(3) a given organism for all antibiotics
(4) a given organism for a given antibiotic
Interpretation:
• The percent essential agreement should be greater than 90%.
