Your results may vary: the imprecision of medical measurements

Abstract

### What you need to know Clinicians and patients need to interpret a multitude of medical measurements. These are often central to monitoring health and informed decision making. Has the serum cholesterol concentration come down since starting a statin? Have vitamin D levels gone up? Is the dose of thyroid medication correct? An understanding of the imprecision of medical measurements is essential to answer any of these questions. Even when laboratory and industry scientists have optimised their diagnostic testing processes to minimise inaccuracies, there always remains an error in any clinical measurement due to unavoidable, naturally occurring variability. This practice pointer explains the nature of measurement errors and offers a practical guide to both estimating the confidence interval of a single result and deciding if changes between serial laboratory tests reflect true changes or simply fluctuations based on analytical or biological variation. ### How this article was made This article was based on a review of the available biological variation data for select routine clinical chemistry measurements as collated by the European Federation of Clinical Chemistry and Laboratory Medicine (https://biologicalvariation.eu/) and in select cases identified by …

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