Biological variation: a rapidly evolving aspect of laboratory medicine

When serial results from examinations of a measurand in laboratory medicine are made in an individual, they are unlikely to be identical over time, even when the state of health or disease in that person has not changed. In part, this is because there are many sources of variation in the pre-examination, examination and post-examination phases of generating a result. However, intrinsic biological variation additionally contributes, often being the most important source of variation. Some measurands have biological variation over the span of life, with important changes at times of rapid physiological development such as the neonatal period, puberty, and the menopause.