Response: importance of screening for macroprolactin in hyperprolactinaemic sera.

As in many other clinical cases, we cannot stress enough the importance of correlating the laboratory results with the patient’s clinical signs and symptoms. Whenever a very high result for prolactin level is seen in the absence of any clinical features of hyperprolactinaemia, a physician should be alerted to the possibility of the patient having a case of macroprolactinaemia. The polyethylene glycol (PEG) precipitation as a screening method to exclude the presence of macroprolactin is affordable and simple to perform. We agree that this method could be made available whenever a case of macroprolactinaemia needs to be excluded. The laboratory result should preferably contain the recovery value (in percentage<40%) given together with the real value of PRL in mIU. In borderline cases (40%-60% recovery), the true PRL value can be obtained from gel filtration chromatography (GFC) which is the reference technique to separate the monomeric prolactin from the macroforms. This method is however, more tedious and requires proper training of staff to perform it. Hence, the PEG precipitation method is sufficient to screen for pseudohyperprolactinaemia caused by the presence of macroprolactin in treated serum with a recovery of less than 40%. 3-8, 9 We would also like to highlight the importance of comparing the recovery value of PRL after PEG precipitation to an appropriate reference interval which can be suggested by the manufacturer but the best means to identify patients with true hyperprolactinaemia accurately is using the reference interval established in the local settings.