Even if it seems trivial at first glance, the correct interpretation of a laboratory result is not an easy task. Indeed, behind any laboratory result, different factors may be present and influence the real value of the result. These factors are generally poorly known by the clinician, which can sometimes unfortunately cause some misinterpretation of the results. In this chapter, we will present the different sources of variations that can influence an analytical result: the pre-analytical and the analytical variations. We will also discuss two essential keys to correctly interpret a laboratory result: the reference value concept and the reference change value (also called the critical difference). After reading this chapter, clinicians should have a better insight on the complexity of the biological analyses, which could help them in their clinical practice.
Keywords: Analytical variation, reference value, critical difference