Reference ranges in hemostasis testing: necessary but imperfect

Most tests performed in laboratories rely on comparison of a test result, typically a patient sample, against a range of values defined for normal healthy individuals, the concept being that any result that lies outside this range thereby defines a (potentially) ‘abnormal’ test result. Indeed, it is difficult to otherwise conceptualize an alternative approach in laboratory diagnostics so far. This process comprises an established standard also within hemostasis testing, and can therefore be defined as ‘necessary’ to establish a deviation from the norm. However, the limitations imposed by this practice are often under-recognized.