# Prolactin blood test: what it measures

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A pituitary hormone that rises with sleep, stress, and a recent meal, so the sample conditions matter.

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Prolactin is a hormone made by the pituitary gland, and it is measured in serum to help assess pituitary and reproductive hormone function. It rises with sleep, stress, exercise, and a recent meal, so sample conditions matter. It is read with other hormones, medicines, and symptoms. The range printed on your report decides how the value is read.

Prolactin is unusual among hormones in how easily ordinary circumstances move it. A stressful morning, a late breakfast, or a difficult blood draw can all leave a mark on the result.

## What the test measures

Prolactin is produced by the front of the pituitary gland, a small structure at the base of the brain. Its best-known role is supporting milk production, and it also influences reproductive hormones by dampening the signals that drive the ovaries and testes. Unlike most pituitary hormones, it is controlled mainly by inhibition: the hypothalamus releases dopamine, which restrains prolactin release, so anything that reduces dopamine signalling can raise prolactin.

Prolactin rises during sleep and is usually higher in the early morning, falling after waking, and it rises substantially in pregnancy and during breastfeeding. A blood test measures the total prolactin concentration in serum. Some laboratories also measure macroprolactin, a large form bound to an antibody, when a result is unexpectedly high, because it can raise the measured value without the same biological effect. That is why a report may mention a macroprolactin screen.

## Why it may be ordered

- As part of a hormone panel, with testosterone or oestradiol, and with thyroid function.
- When pituitary function is being assessed, or when a pituitary condition is being followed.
- When menstrual changes, absent periods, or fertility is being investigated.
- When breast milk production occurs outside breastfeeding, or when breast enlargement or low libido is being assessed in men.
- When a medicine known to raise prolactin is being taken, because the result is read with the medicine list.
- When a low thyroid result is being assessed, because a low thyroid can raise prolactin.

## The unit on your report

| What you may see | Unit | What it reflects |
| --- | --- | --- |
| Prolactin, PRL | ng/mL | The prolactin concentration in serum, in nanograms per millilitre. |
| Prolactin, PRL | ug/L | The same concentration in micrograms per litre. For prolactin the two units give the same number, because both are mass per volume. |
| Prolactin, serum | ng/mL or ug/L | The sample type. Serum is usual, and the unit follows the laboratory's convention. |
| Macroprolactin, prolactin after screening | as the laboratory reports | A laboratory measurement of the large bound form, reported when a screen has been done. |

If a report mentions a macroprolactin result or a recovery figure, that note belongs with the value. It is the laboratory telling you that part of the measured prolactin may be in a form that behaves differently.

## Why this page does not print a range

Prolactin ranges differ by laboratory and assay, by sex, and by pregnancy and breastfeeding status, and paediatric ranges differ with age. Some reports print separate ranges for men and women, and some print a single range for both. The conditions of collection matter as well: a sample taken after a short sleep, a painful draw, or a recent meal can sit higher than a sample taken under quieter conditions.

The range printed on the report that produced your value is the one that applies. Doctano keeps that printed range with the result and does not replace it with a general range. Where a report prints sex-specific ranges, the one that matches the person is the one to read.

## What a high value can mean

A result above the report's range means the prolactin concentration is higher than the laboratory's interval. Possible contributors include pregnancy and breastfeeding, sleep, stress, pain, exercise, and a recent meal; some medicines, including antipsychotics, some antidepressants, some anti-nausea medicines, and opioids; a low thyroid result; kidney disease; and pituitary conditions such as a prolactin-producing adenoma or a lesion that presses on the pituitary stalk.

Macroprolactin is another possible explanation for a raised result, and it is why a laboratory may run a screen. A raised value does not confirm or rule out any of these, and a clinician reads it with the medicine list, thyroid function, and the other hormone results.

## What a low value can mean

A result below the report's range means the prolactin concentration is lower than the laboratory's interval. Low prolactin is less often interpreted on its own. It can appear when the pituitary produces less of several hormones, and in that setting it is read with the other pituitary results, including thyroid function and cortisol.

A low result after pregnancy or breastfeeding is expected in some circumstances, and a single low value without context usually says little. A clinician decides whether a low prolactin fits the rest of the picture.

## What can move the value

- **Sleep and the time of day.** Prolactin rises during sleep and falls after waking, so the hour of collection matters.
- **Stress and pain.** The blood draw itself, and the anxiety around it, can raise the value.
- **Recent food and exercise.** Both can raise prolactin for a period after the event.
- **Pregnancy and breastfeeding.** Both raise prolactin substantially and are part of how the result is read.
- **Medicines.** Antipsychotics, some antidepressants, some anti-nausea medicines, and opioids can raise prolactin, and a clinician can say whether a medicine is relevant.
- **Kidney and thyroid function.** Reduced kidney clearance and a low thyroid result can both raise prolactin.

## What to compare it with

Read prolactin with thyroid function, because a low thyroid result is a common contributor; with testosterone or oestradiol, because prolactin affects gonadal function; with LH and FSH; and with kidney function. Where a result is high, a clinician may look at the macroprolactin screen and at a repeat sample taken under calmer conditions.

## How to see the trend

Doctano reads the prolactin value, its unit, and the reference range printed on the report. It keeps the range with the result, normalizes the marker name across laboratories, and places the value on the profile's timeline. Each point still opens the report it came from, so a note about macroprolactin stays with the value it describes.

Verify the value and the unit against the original report before treating a change as real. A change is easier to interpret when both samples came from the same laboratory under similar conditions.

## What this page is not

This page explains the test in general. It does not interpret your result, diagnose a condition, or recommend treatment. It is not medical advice. Verify the value and the unit against the original report, and discuss the result with a qualified professional.

## Prolactin questions

**What does a prolactin blood test measure?**

It measures the concentration of prolactin, a hormone made by the pituitary gland, in serum. Prolactin supports milk production and also influences reproductive hormones, and its release is restrained by dopamine from the hypothalamus.

**Why can a prolactin result be higher on one day than another?**

Prolactin rises with sleep, stress, pain, exercise, and a recent meal, and the blood draw itself can raise it. Values also vary between samples, which is why a single result is read with the conditions in which it was taken.

**What is macroprolactin?**

Macroprolactin is a large form of prolactin bound to an antibody, and it is cleared more slowly than the usual form. Some laboratories screen for it when a result is unexpectedly high, because it can raise the measured value without the same biological effect.

**Can a raised prolactin result have more than one explanation?**

Yes. Possible contributors include stress and recent meals, pregnancy and breastfeeding, some medicines, a low thyroid result, kidney disease, and pituitary conditions. A raised value does not confirm or rule out any of them on its own.

## Limits

**This is not a diagnosis.** Prolactin is read with your medicines, your other hormone results, and the range printed on your report. Verify the value against the original report and discuss it with a qualified professional.

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