What Are Normal Prolactin Levels by Age?

Prolactin is a pituitary hormone best known for starting milk production, and in most healthy adults it stays at a low level. There is no single normal number, though, because what counts as normal shifts with sex and with life stage, from birth through pregnancy and menopause. The level also moves from hour to hour and with stress, so a reading just over your lab’s range is often not a sign of illness.

Normal Prolactin Levels by Age and Sex

Women’s prolactin is higher than men’s whether they are fasting or have just eaten.9PubMed Central. Effect of Age, Gender, Food Intake, Obesity, and Smoking on Serum Levels of Prolactin in Healthy Adults Units can make a normal number look strange. The units ng/mL and µg/L give the same number. The units µIU/mL or mU/L are a different scale, international units, where roughly 21 units equal 1 ng/mL. Check which unit is printed beside your number before comparing it with anything online. To convert, divide by about 21: a result of 500 mU/L is roughly 24 ng/mL, near the top of the usual range and not a dramatic figure.

Your own report’s reference range is the first yardstick, since each lab sets slightly different cutoffs based on its equipment and the people it tested. The ranges here are for non-pregnant adults, so they don’t apply to a pregnant woman, a nursing mother, or a baby.

A newborn’s high number is expected, since the baby is exposed to the mother’s pregnancy hormones before birth. If a parent sees a high result on an infant’s report, the useful question is which age-specific range the lab used, since an adult range would make a normal baby look abnormal.

How Your Menstrual Cycle and Time of Day Change the Number

Prolactin climbs in the days before ovulation and peaks around the surge of the egg-release hormone.10PubMed. Serum prolactin levels during the menstrual cycle It stays higher in the second half of the cycle than in the early days after a period starts.11PubMed. Prolactin levels during the menstrual cycle The exact peak day differs from cycle to cycle.12PubMed. Prolactin levels during the menstrual cycle

Time of day matters too. Prolactin is released in pulses and is higher at night, with peaks most often between 11 pm and 7 am.13PubMed. Prolactin circadian rhythm persists throughout lactation in women A test drawn soon after waking can therefore read higher than one taken later in the morning. Because release comes in pulses, two draws an hour apart can differ, so doctors judge repeated values rather than one reading. Many doctors ask for a sample a few hours after you get up rather than first thing, though instructions differ, so it is worth asking the clinic whether they want a particular time.

Noting which day of your cycle the test falls on helps the doctor interpret a slightly high result. If a borderline result came late in the cycle, a repeat early in the cycle may read lower.

Prolactin During Pregnancy and Breastfeeding

Average levels rise from about 27 ng/mL in the first trimester to about 82 in the second and about 205 in the third.14PubMed. Prolactin synthesis and release during pregnancy and puerperium One lab’s third-trimester range ran from about 4,100 to 9,700 µIU/mL.15PubMed. Serum prolactin levels across pregnancy and the establishment of reference intervals

That is why pregnancy is checked first when a result is high. Pregnancy can explain a high number, so doctors usually rule it out before ordering anything else. If a pregnancy is possible, a home test is a quick first step.

Mothers nursing more than six times a day keep high prolactin through the first year.16Journal of Biosocial Science. The influence of the frequency of nursing and of previous lactation experience on serum prolactin in lactating mothers Those nursing fewer than four times a day fall back to non-nursing levels by about six months after birth.17Journal of Biosocial Science. The influence of the frequency of nursing and of previous lactation experience on serum prolactin in lactating mothers The night-time high persists through breastfeeding.18PubMed. Prolactin circadian rhythm persists throughout lactation in women

Low prolactin can matter too, because prolactin tells the breast to make milk and too little can reduce a mother’s supply. Heavy blood loss during childbirth can damage the pituitary gland, which can leave prolactin too low. Clues include trouble producing milk along with thinning underarm or pubic hair. If these signs appear, doctors check a range of pituitary hormones, not prolactin alone.

Prolactin After Menopause and in Older Men

Women’s levels drop clearly by the second year after menopause.19PubMed. Changes in prolactin levels with the menopause: the effects of estrogen/androgen and calcitonin treatment With lower estrogen, postmenopausal women have prolactin patterns similar to men’s.20PubMed. Prolactin Pulsatile Characteristics in Postmenopausal Women Higher-dose estrogen therapy can raise prolactin, but only to the levels of younger women.21PubMed. The effect in post-menopausal women of natural human and artificial oestrogens on the concentration in serum of prolactin Standard doses often leave it unchanged. If you are on therapy, tell your doctor your dose before testing. Women over 80 may see a slight rise again.22PubMed. Serum Prolactin and Aging: Basal Values and Changes With Estrogen Use and Hypothyroidism

Men’s prolactin creeps up slightly with age.23PubMed. Serum Prolactin and Aging: Basal Values and Changes With Estrogen Use and Hypothyroidism Some healthy men over 75 had levels between 20 and 40 ng/mL.24PubMed. Basal serum prolactin levels and prolactin responses to constant infusions of thyrotropin releasing hormone in healthy aging men A mildly raised result in a very old man is therefore not automatically abnormal.

Why a Result Can Be High When Nothing Is Wrong

Physical or emotional stress, a high-protein meal, hard exercise, sex and nipple or chest stimulation can raise levels temporarily.25Acibadem Hospitals Group. Prolactin Levels: Why They Fluctuate & Proper Testing Even the stress of the blood draw can raise prolactin, and 30 minutes of rest may not be enough to settle it.26PubMed Central. Pool vs single sample determination of serum prolactin to explore venipuncture associated stress induced variation Some labs take a second sample after an hour of rest and test both together.27PubMed Central. Pool vs single sample determination of serum prolactin to explore venipuncture associated stress induced variation

If you need a retest, avoid hard exercise, sex and breast or nipple stimulation the day before. Skip a large protein-rich meal just before the draw. Sit quietly before the sample is taken, and tell the staff if needles make you anxious.

Some people carry macroprolactin, a large, mostly inactive form that tests count as prolactin.28Clinical Chemistry. Serum Total Prolactin and Monomeric Prolactin Reference Intervals Determined by Precipitation with Polyethylene Glycol: Evaluation and Validation on Common ImmunoAssay Platforms It can make a level look high and lead to wrong diagnoses.29Clinical Chemistry. Serum Total Prolactin and Monomeric Prolactin Reference Intervals Determined by Precipitation with Polyethylene Glycol: Evaluation and Validation on Common ImmunoAssay Platforms It is the third most common non-pregnancy cause of high prolactin, after medicines and tumors.30PubMed. Pitfalls in the Diagnostic Evaluation of Hyperprolactinemia Different lab machines detect it differently, so results can vary between labs.31PubMed Central. Prolactin Biology and Laboratory Measurement: An Update on Physiology and Current Analytical Issues When tracking your level over time, use the same lab so changes reflect your body and not the method. If the number stays high without symptoms, ask whether the lab can check your sample for big, mostly inactive prolactin.

When High Prolactin Points to a Medical Cause

Medicines are the most common non-pregnancy cause of high prolactin.32PubMed. Pitfalls in the Diagnostic Evaluation of Hyperprolactinemia Antipsychotics lead the list, along with some antidepressants, blood pressure drugs and gut-motility drugs.33PubMed. Drugs and prolactin They block dopamine, which normally keeps prolactin down.34PubMed Central. Management of antipsychotic-induced hyperprolactinemia Risperidone raises prolactin in 70 to 100 percent of users.35PubMed Central. Management of antipsychotic-induced hyperprolactinemia

If you take one of these, never stop a psychiatric or other prescribed medicine on your own, since stopping suddenly can cause harm worse than a high prolactin level. Ask your prescriber whether an alternative that raises prolactin less is suitable. Bring a full list of everything you take, including over-the-counter products and supplements, to the testing visit.

An underactive thyroid and kidney failure can also raise prolactin and should be checked before imaging.36PubMed. Pitfalls in the Diagnostic Evaluation of Hyperprolactinemia A level above 250 ng/mL strongly suggests a prolactinoma, a benign prolactin-making pituitary tumor, though some medicines can also push levels this high.37PubMed. Pitfalls in the Diagnostic Evaluation of Hyperprolactinemia

High prolactin can cause milky nipple discharge, irregular or absent periods and fertility problems.38Deneysel ve Klinik Tıp Dergisi. Hyperprolactinemia and infertility in male and female In men it can lower libido and cause erectile problems, mainly when above about 35 ng/mL.39PubMed. Hormonal causes of male sexual dysfunctions and their management (hyperprolactinemia, thyroid disorders, GH disorders, and DHEA) Over years it can thin bones.40PubMed. From galactorrhea to osteopenia: rethinking serotonin-prolactin interactions

The usual first step is to repeat the test under calm conditions, since the first result may have been a temporary rise. If it stays high, doctors check pregnancy, thyroid function and kidney function. A pituitary MRI usually comes only if no other cause explains the result. How quickly doctors move depends on symptoms, such as headaches, vision changes, absent periods or discharge, and on how high the level is.

Can a Prolactin Result Be Falsely Low

When prolactin is extremely high, it can overwhelm the test and give a falsely low reading.41PubMed Central. The Hook Effect: A Case Study of a Giant Invasive Prolactinoma With Falsely Low Serum Prolactin This mostly happens with pituitary tumors larger than 10 mm.42Mayo Clinic Laboratories. Prolactin, Pituitary Macroadenoma, Serum In one case a reading of about 165 ng/mL was really 26,000 when the sample was diluted.43PubMed. “Hook effect” in prolactinomas: case report and review of literature Dilution means the lab thins the sample before measuring again, which brings the prolactin back into the range the test can count.

Some situations justify asking about it. Persistent headaches or vision changes together with hormone symptoms raise the possibility of a large pituitary tumor. A large pituitary mass on a scan alongside a normal prolactin result deserves a second look at the lab method. Ongoing nipple discharge or missed periods despite normal numbers are reasons to ask whether the lab diluted the sample.