Reference Value Advisor: a new freeware set of macroinstructions to calculate reference intervals with Microsoft Excel

Abstract

International recommendations for determination of reference intervals have been recently updated, especially for small reference sample groups, and use of the robust method and Box-Cox transformation is now recommended. Unfortunately, these methods are not included in most software programs used for data analysis by clinical laboratories. We have created a set of macroinstructions, named Reference Value Advisor, for use in Microsoft Excel to calculate reference limits applying different methods. For any series of data, Reference Value Advisor calculates reference limits (with 90% confidence intervals [CI]) using a nonparametric method when n≥40 and by parametric and robust methods from native and Box-Cox transformed values; tests normality of distributions using the Anderson-Darling test and outliers using Tukey and Dixon-Reed tests; displays the distribution of values in dot plots and histograms and constructs Q-Q plots for visual inspection of normality; and provides minimal guidelines in the form of comments based on international recommendations. The critical steps in determination of reference intervals are correct selection of as many reference individuals as possible and analysis of specimens in controlled preanalytical and analytical conditions. Computing tools cannot compensate for flaws in selection and size of the reference sample group and handling and analysis of samples. However, if those steps are performed properly, Reference Value Advisor, available as freeware at http://www.biostat.envt.fr/spip/spip.php?article63, permits rapid assessment and comparison of results calculated using different methods, including currently unavailable methods. This allows for selection of the most appropriate method, especially as the program provides the CI of limits. It should be useful in veterinary clinical pathology when only small reference sample groups are available.

Colorimetric and electrophoretic evaluation of lipoprotein fractions in healthy neonatal calves: Comparison with results from adult cows and from calves with inflammatory conditions

“…PON-1 activity, expressed as U/mL, is defined as 1 nmol of p-nitrophenol formed per minute. (Geffré et al, 2011). Results yielding a Pvalue <0.05 were considered as statistically significant.…”

Reference intervals for 24 laboratory parameters determined in 24-hour urine collections

“…The reference intervals were determined for all participants as well as for women and men separately as the central 95% of the measurement results according to the CLSI C28-A3 statistical guidelines [1] using Reference Value Advisor [9], a set of macroinstructions for Microsoft Excel (Microsoft, Redmond, WA, USA) developed for this purpose. The 2.5th and the 97.5th percentiles of the distribution of the test results represent the lower and the upper reference limit, respectively, and were annotated with 90% [11] of the data to approximate a normal distribution.…”

Extravascular hemolysis and complement consumption in Paroxysmal Nocturnal Hemoglobinuria patients undergoing eculizumab treatment

“…The horizontal line represents the minimal concentration (110g/mL) of free eculizumab required for blocking completely the lytic pathway. The same line also corresponds to the upper limit of the normal levels of plasma sC5b-9 in this assay, calculated using reference value advisor v2.1 as described by Geffre et al (Geffre, et al, 2011).…”