Prolactin

What it measures

Prolactin is a pituitary hormone that stimulates milk production. It is measured in galactorrhoea, amenorrhoea, infertility, low libido and suspected pituitary tumours.

Specimen and preparation

• Specimen: Serum or lithium-heparin plasma
• Tube: Gold top
• Preparation: Collect at least 2–3 hours after waking, at rest; avoid breast stimulation and stress before sampling.

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Prolactinoma
• Pregnancy and breastfeeding
• Dopamine-blocking drugs (antipsychotics, metoclopramide)
• Primary hypothyroidism
• Stalk compression by other pituitary masses
• Macroprolactin (inactive form)

Causes of low values

• Pituitary failure (Sheehan syndrome)
• Dopamine agonists (cabergoline, bromocriptine)

Method

Chemiluminescent immunoassay; PEG precipitation for macroprolactin

Good to know

Screen for macroprolactin when prolactin is high without symptoms. Very large tumours can give falsely low results (hook effect); dilute the sample.

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