The rise in prolactin is seen after generalized tonic-clonic or partial complex seizures. The peak level is seen 15-20 minutes after the event. The half-life of the prolactin is about 20 minutes, and there is a return to pre-ictal levels after 60 minutes.
Sample collection should be standardized for optimum usability:
(1) Ideally this would be 20-30 minutes after the episode. A sample more than 60 minutes after the seizure will likely be a false negative.
(2) Baseline level, either drawn more than 60 minutes after the seizure or on a day without seizure activity.
Criteria for elevations in serum prolactin seen in epileptic seizures:
(1) A level 2 times baseline levels (some use 3 times baseline).
(2) A level more than 3 standard deviations above the baseline.
Serum prolactin levels can help distinguish pseudoseizures from true seizures. However, this may be limited:
(1) by the prevalence of pseudoseizures in the population (see Table 2, page 1225, Yerby et al, 1987).
(2) in patients with concurrent epilepsy and pseudoseizures
The absence of a rise in prolactin does not exclude the diagnosis of epilepsy. Prolactin levels will not be elevated if (Sperling et al):
(1) the seizure was brief (< 10 seconds), or
(2) there was no loss of consciousness.
A sample drawn more than 60 minutes after the event will miss an elevated value.
