Abstract: A sample age monitor for monitoring the age of a biological sample, said sample age monitor comprising a release device to provide an age indicator into a medium preferably comprising the sample substantially predictably such that an age estimate of the sample is determinable by measuring a level of the age indicator. A biological sample holder including the sample age monitor is also described. The device may be employed to determine the age of a blood sample, and hence whether the results of lab analysis of the sample are reliable. In one embodiment the release device comprises a container holding a storage medium storing the age indicator. The age indicator may comprise a metal, in particular lithium, ion.