Prolactin Test – Complete, Simple, and Patient-Friendly Guide
Introduction
The Prolactin Test is a simple blood test that measures the level of prolactin, a hormone produced by the pituitary gland. Although prolactin is best known for supporting breast milk production in women after childbirth, it also plays important roles in fertility, menstrual cycles, and sexual health in both men and women.
Doctors commonly recommend this test to investigate symptoms such as irregular periods, unexpected breast milk leakage, infertility, decreased libido, or signs of pituitary gland disorders. Because prolactin affects several parts of the reproductive system, checking its level provides valuable insight into hormonal balance and underlying medical conditions.
What is Prolactin?
Prolactin is a hormone secreted by the anterior pituitary gland, located at the base of the brain. Its release is primarily controlled by dopamine, a neurotransmitter that inhibits prolactin secretion under normal conditions. When dopamine levels decrease, prolactin levels naturally rise.
Although prolactin is strongly associated with breastfeeding, it also influences reproductive health, sexual function, mood regulation, and metabolic activity in both genders. Measuring prolactin helps identify whether the pituitary gland is working properly and whether hormone levels are stable.
Where is Prolactin Produced in the Body?
Prolactin is produced in the anterior pituitary, but its regulation involves communication between multiple parts of the body.
How Production Works:
- The hypothalamus releases dopamine which suppresses prolactin production.
- During pregnancy, dopamine suppression decreases and prolactin levels rise.
- Prolactin is released into the bloodstream and affects breast tissue, reproductive organs, the brain, and immune cells.
This is part of the hypothalamic–pituitary axis, a complex hormonal system that ensures reproductive and stress-related hormones remain in balance.
Functions and Importance of Prolactin
Prolactin performs several important roles that differ slightly between females and males.
In Females
- Breast development: Supports breast tissue growth during pregnancy.
- Milk production: Stimulates lactation after childbirth.
- Menstrual regulation: Prolactin influences ovulation and affects estrogen production.
- Fertility: Helps maintain the hormonal balance required for conception.
In Males
- Supports testosterone regulation: Helps maintain reproductive hormone balance.
- Sexual satisfaction and mood: Plays a role in emotional stability and sexual behavior.
- Possible influence on immunity: May support immune system activity.
Although prolactin is typically low in men, abnormal levels can significantly affect sexual health and fertility.
Causes of Low Prolactin Levels
Low prolactin levels are rare. When they occur, they usually indicate pituitary gland problems or medication effects.
Common Causes
- Hypopituitarism: Reduced pituitary hormone production.
- Dopamine agonist medications: Drugs like bromocriptine or cabergoline reduce prolactin.
- Head injury: Damage to the pituitary region.
- Pituitary tumor pressure: Growth pressing on normal pituitary cells.
- Severe postpartum hemorrhage: Known as Sheehan’s syndrome.
Symptoms of Low Prolactin Levels
In Females
- Difficulty producing breast milk after childbirth
- Reduced fertility (rare)
- Low estrogen-related symptoms
In Males
- Generally no noticeable symptoms
- Occasionally reduced libido or mild mood changes
Although low prolactin is usually less concerning, it becomes important when linked to pituitary gland failure or multiple hormone deficiencies.
Causes of High Prolactin Levels
High prolactin levels (hyperprolactinemia) are much more common than low levels. Elevated levels can occur naturally, due to medications, or because of medical conditions affecting the pituitary or thyroid.
Common Medical Causes
- Prolactinomas: Benign pituitary tumors that produce excessive prolactin
- Hypothyroidism: Low thyroid hormone increases TRH, which raises prolactin
- Chronic kidney disease: Reduced hormone clearance
- Chronic liver disease: Impaired hormone metabolism
- PCOS (in some cases)
- Severe stress or anxiety
- Intense physical activity
Medication-Related Causes
Several medicines significantly increase prolactin levels:
- Antipsychotics: Risperidone, haloperidol
- Antidepressants: SSRIs, tricyclics
- Anti-nausea medications: Metoclopramide
- Blood pressure drugs: Methyldopa
- Estrogen-based contraceptives
Natural Causes
- Pregnancy
- Breastfeeding
- Deep sleep
- Sexual activity
- Nipple stimulation
Symptoms of High Prolactin Levels
High prolactin can affect menstrual cycles, fertility, sexual function, and breast tissue.
In Females
- Irregular or absent menstrual periods
- Difficulty conceiving
- Galactorrhea: Milk discharge unrelated to pregnancy
- Hot flashes or vaginal dryness
- Breast tenderness
- Low libido
In Males
- Reduced sex drive
- Erectile dysfunction
- Low sperm count
- Enlarged breast tissue (gynecomastia)
- Fatigue or signs of low testosterone
If a prolactinoma becomes large, it may cause:
- Persistent headaches
- Blurred or reduced peripheral vision
These symptoms occur due to pressure on surrounding nerves in the brain.
Reference (Normal) Ranges
Normal values may differ slightly depending on the laboratory.
Typical Ranges
- Non-pregnant women: 4.8 – 23.3 ng/mL
- Pregnant women: 80 – 400 ng/mL (varies by trimester)
- Men: 4.0 – 15.2 ng/mL
- Children: Usually under 10 ng/mL
Interpretation
- High prolactin → May indicate pituitary tumor or thyroid disorder
- Low prolactin → May indicate pituitary insufficiency
Sample Type
- Sample: Serum (blood sample)
- Tube Used: Red Top (Plain) or SST
- Fasting: Not required, but morning samples give more accurate results
Test Preparation
To ensure accurate results, follow these recommendations:
- Avoid stress 24 hours before testing
- Avoid intense exercise
- Avoid nipple stimulation or sexual activity for 12–24 hours
- Inform your doctor about medications that raise prolactin
- Morning sample preferred due to hormone fluctuations
Blood is drawn from a vein, and results usually come within 24 hours.
When to Consult a Doctor
You should see a doctor if you experience:
- Irregular or missed periods
- Unexplained breast milk discharge (galactorrhea)
- Difficulty becoming pregnant
- Low libido or sexual dysfunction
- Enlarged breasts in men
- Persistent headaches or visual problems
Your doctor may order additional tests such as:
- TSH test to evaluate thyroid function
- MRI of the pituitary gland if a tumor is suspected
- Estrogen, testosterone, or FSH/LH tests for full hormonal evaluation
Early diagnosis helps prevent long-term complications.
Important Word Explanations
Prolactin: Hormone essential for milk production and reproductive function.
Pituitary Gland: Small brain gland that regulates most hormone systems.
Dopamine: Neurotransmitter that inhibits prolactin release.
Prolactinoma: Benign tumor of the pituitary gland producing excess prolactin.
Galactorrhea: Unusual milk discharge unrelated to pregnancy or breastfeeding.
Hypopituitarism: Low pituitary hormone production affecting multiple body functions.
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