Overview :

Clinical interpretations of antibiotic susceptibility results rely on them being analytically reliable. Part of quality management of susceptibility results is to compare results of a test method with results from a reference method. One comparison involves the reporting of qualitative susceptibility categories.

Possible results for each method:

(1) susceptible

(2) intermediate or moderately susceptible

(3) resistant

This gives 9 possible combinations (3 * 3) for reference to test results.

percent very major errors =

= (number of very major errors) / (number of organism susceptibility test results) * 100%

percent major errors =

= (number of major errors) / (number of organism susceptibility test results) * 100%

percent minor errors =

= (number of minor errors) / (number of organism susceptibility test results) * 100%

percent category agreement =

= (number of agreements) / (number of organism susceptibility test results) * 100%

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:

• Ideally there should be complete agreement between the reference and test results.

• Major and very major errors should be < 5% with very major errors <= 1.5% (FDA, Thornsberry).

Food and Drug Administration (FDA). Review criteria for assessment of antimicrobial susceptibility devices. Revised version. 1991.

Hindler J. Section 5: Antimicrobial susceptibility testing. page 5.23.5-5.23.8. IN: Isenberg HD (editor). Clinical Microbiology Procedures Handbook, Supplement 1. ASM Press. 1994.

Thornsberry C. Automated procedures for antimicrobial susceptibility tests. pages 1015-1018. IN: Lennette EH, Balows A, et al (editors). Manual of Clinical Microbiology. 4th Edition. ASM Press. 1985.