The BV calculator: a free, open-source web app for estimation of within-subject and between-subject biological variation

Abstract Objectives Biological variation (BV) data are essential for many purposes in laboratory medicine, however, the complex statistical analysis remains a barrier for delivery of BV data. This study describes the development of a web-based BV Calculator based on the Biological Variation Data Critical Appraisal Checklist (BIVAC). Methods We developed an open-source BV Calculator ( https://bvcalculator.streamlit.app/ ) using Python 3.12, built on the 14 quality items (QI) included in the BIVAC. It requires manual user input with uploading of raw data and manual selection of QIs related to the study and study population, followed by automated preprocessing of the data with outlier detection, variance homogeneity assessment, steady-state verification through linear regression, normality assessment with Shapiro-Wilk tests, and log transformation when appropriate. The tool uses nested two-level ANOVA for BV component estimation and supports both balanced and unbalanced study designs and delivers CV I and CV G data with 95 % confidence intervals, accompanied by BIVAC criteria and audit logs. Real world data for creatinine, total cholesterol, S100B and creatine kinase from the European Biological Variation Study (EuBIVAS) were assessed, and results compared to previously published EuBIVAS data derived by manual processing. Results Central BV components, including mean concentrations, CV A , CV I , and CV G estimates were similar to the manual EuBIVAS estimates for all measurands. Substantial differences in the number of subjects retained following automated outlier and trend analyses were identified for creatinine and S100B. Conclusions The BV Calculator is a freely available tool that can be used to facilitate BIVAC compliant statistical analysis of BV data.