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Overview :
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%.
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