The panel / Androgens
Prolactin
Prolactin is not a routine men's health test and should not be sold as one. It earns its place in one specific situation: when testosterone is low and the pituitary signal is low with it. In that setting it can find a treatable pituitary problem, or more often, a medication nobody connected to the symptoms.
What it measures
Prolactin is a pituitary hormone. When it runs high it suppresses the signal that drives testosterone production, which is how it produces low libido, erectile symptoms and fatigue that look identical to primary low testosterone. Finding it matters because the cause is often removable.
This is why prolactin is drawn on a secondary pattern rather than on everyone. On a primary pattern it adds nothing, and a normal result on a man with no indication is a test that should not have been run.
Draw conditions matter more here than for most tests. The stress of a difficult venipuncture alone can raise prolactin, as can exercise, a non-fasting sample, or chest wall stimulation. A single result above the reference range is considered diagnostic provided the draw was clean, and dynamic stimulation testing is specifically not recommended.
Why it is on the panel
Because a pituitary cause and an opioid cause look identical on a testosterone result alone, and both are missed by panels that stop at testosterone. Current guidance is to measure it in men with a secondary pattern, particularly those under 50, and in anyone with headaches, visual changes or markedly low gonadotropins.
Interpretation
Reading the result
How high it is narrows the cause considerably, which is why the actual number matters here more than on most of this panel.
Two traps are worth knowing about. Macroprolactin is an inactive form bound to antibody that falsely raises the result, and accounts for around a fifth of high readings. It is screened for when the number does not fit the man. The hook effect is the opposite: a very large tumour can saturate the assay and produce a falsely low result, which is why a large pituitary mass with an unimpressive prolactin gets the sample re-run diluted.
What raises prolactin without a pituitary tumour
Medication is the most common cause by some distance, and most of it is easy to identify once looked for.
What happens next
A mildly raised result is repeated under proper conditions before anything else happens, because the draw itself is the most common explanation.
If a drug is the likely cause and it is safe to pause it, it is stopped for a few days and the level rechecked. If it cannot be stopped, imaging is the route instead.
Thyroid and kidney function are checked, because both raise prolactin and both are simpler explanations than a tumour.
A confirmed and unexplained elevation, or any elevation with headaches or visual change, prompts a contrast pituitary MRI and referral to endocrinology.