Normalized Resistance Interpretation, NRI



 Automatic NRI calculations for MIC distributions, for Windows and MAC (2019 version)  
 Automatic NRI calculations for disc zone histograms, for Windows and MAC (2019 version)  

When you use these programmes, please acknowledge: "The automatic excel programmes were made available through courtesy P.Smith, W.Finnegan, and G.Kronvall." The proper reference is: Smith P, Finnegan W, Ngo T, Kronvall G. Influence of incubation temperature and time on the precision of MIC and disc diffusion antimicrobial susceptibility test data. Aquaculture 2018; 490:19-24.



The method for NRI calculations is patented, European patent No 1383913, US Patent No. 7,465,559. The use of NRI in pure research is recommended and provides a powerful tool for analysing MIC and zone size distributions in individual laboratories. For commercial applications a license is required. Request further information from the patent holder, Bioscand AB, Täby, Sweden.


In research publications, include the following statement:

"The NRI method was used with permission from the patent holder, Bioscand AB, TÄBY, Sweden (European patent No 1383913, US Patent No. 7,465,559)."



a/ original references to the NRI principles and to the analysis of inhibition zone diameter distributions:

1. Kronvall G, Kahlmeter G, Myhre E, Galas MF. A new method for normalized interpretation of antimicrobial resistance from disk test results for comparative purposes. Clin Microbiol Infect 2003; 9(2):120-132.

2. Kronvall G. Determination of the real standard distribution of susceptible strains in zone histograms. Int J Antimicrob Agents 2003; 22:7-13.

b/ when analyzing MIC distributions:

3. Kronvall G, Karlsson I, Walder M, Sörberg M, Nilsson LE. Epidemiological MIC cut-off values for tigecycline calculated from Etest MIC values using normalized resistance interpretation. Journal of Antimicrobial Chemotherapy 2006; 57:498-505.

4. Kronvall G. Normalised Resistance Interpretation, NRI, as a tool for establishing epidemiological MIC susceptibility breakpoints. J Clin Microbiol 2010; 48(12):4445-4452.



Some extra programmes:

 NRI for disc zone diameter histograms, Excel sheet (for APMIS vol 124, pp 1023 - 1030, 2016)  
 Download some other programs for clinical microbiology

© G.Kronvall
Updated 2021-01-18