Specimen dilution and result calculation in 24-hour urine testing: Sources of analytical error and practical strategies

Background: Twenty-four-hour urine testing is widely used to quantitatively assess urinary analyte excretion. Still, reliable interpretation depends not only on analytical measurement but also on proper specimen dilution and subsequent result calculation. Errors introduced during these steps may substantially alter reported results, even with an analytically accurate concentration measurement. This narrative mini-review synthesises the principal sources of dilution- and calculation-related error in 24-hour urine testing and outlines practical strategies for prevention and detection. Specimen dilution is considered in relation to analytical measuring intervals, dilution-factor selection, pipetting, and dilution-factor transcription. Calculationrelated vulnerabilities include urine-volume handling, unit conversion, formula selection, normalisation, and laboratory information system and middleware configuration. Particular attention is given to input data integrity and the potential for systematic errors arising from incorrect calculation rules or software configuration. Practical risk-reduction strategies for error prevention and detection include analyte-specific dilution procedures, validated automation, standardised calculation and reporting conventions, electronic transfer of critical input data, plausibility checks, independent verification, and targeted quality assurance. Dedicated evidence quantifying dilution- and calculation-related errors in 24-hour urine testing remains limited. Nevertheless, these steps present important opportunities for error propagation and should be explicitly incorporated into laboratory quality management processes. Standardisation, validated automation, and targeted verification may reduce operator-dependent variability and improve the reliability and clinical usefulness of reported 24-hour urinary excretion results.