Macroprolactinaemia is usually detected by polyethylene glycol (PEG) precipitation in clinical laboratories. Laboratory data on prolactin and macroprolactin screening by PEG precipitation in a tertiary hospital were reviewed in order to revise the local policy for reflex screening and reporting of macroprolactin in patients with hyperprolactinaemia.Paired prolactin results from 464 patients before and after PEG precipitation, either requested by a clinician or performed as a reflex test, were retrieved and reviewed.Recovery of prolactin after PEG treatment was highly variable (3.7 to 97.7%). The distribution of prolactin recovery percentages after PEG precipitation in patients with true hyperprolactinaemia was markedly different from that in patients without true hyperprolactinaemia. The proportion of patients with true hyperprolactinaemia increased gradually with increasing pre-PEG prolactin concentrations; the reverse was true with macroprolactinaemia. Five patients (1.1%) were found to have co-existing macroprolactinaemia and true hyperprolactinaemia.Results from this retrospective study indicate that macroprolactinaemia is common and can be present even in patients with very high serum prolactin concentrations. There is no cut-off limit for pre-PEG serum prolactin concentration that can totally exclude macroprolactinaemia. Moreover, co-existence of true hyperprolactinaemia and macroprolactinaemia in the same patient is not a rare phenomenon. Post-PEG prolactin concentration and percentage recovery should be reported together to guide the interpretation and management of hyperprolactinaemia.