Prolactin is a hormone synthesized and secreted by the prolactin cells of the anterior pituitary gland. It is normally present in the human body. The physiological role of prolactin is extremely broad and complex. In humans, it mainly promotes the development and growth of the secretory tissues of the mammary glands, initiates and maintains lactation, and increases protein synthesis by the mammary cells. Prolactin is a hormone synthesized and secreted by the prolactin cells of the anterior pituitary gland. It is normally present in the body. The physiological effects of prolactin are extremely broad and complex. In humans, it mainly promotes the development and growth of the secretory tissues of the mammary glands, initiates and maintains lactation, and increases protein synthesis by the mammary cells. Prolactin can also affect gonadal function and, in addition, is associated with autoimmune function. Therefore, this is included when performing endocrine hormone tests related to reproduction, regardless of male and female. What is hyperprolactinemia (HPRL) and what are the diagnostic indicators A state in which peripheral serum prolactin levels are persistently higher than normal for various reasons is called HPRL and can be diagnosed by measuring endosomal prolactin levels. Prolactin levels in normal women of childbearing age do not exceed 1.14-1.36 nmol/L (25-30 ng/ml) (each laboratory has its own normal values). Since the diagnosis of hyperprolactinemia is based on serum prolactin measurements, standardized blood specimen collection and accurate and reliable laboratory measurements are especially important for the diagnosis of HPRL, especially in cases of mildly elevated prolactin levels, which sometimes require 2-3 repeat measurements. There are many causes of elevated prolactin. The diagnosis of HPRL can only be made after a comprehensive analysis of clinical manifestations and serum prolactin levels. What to look for when taking a blood test for prolactin: Since serum prolactin levels are affected by its pulsatile secretion and different secretion during the day and night, the time of blood collection should be at the lowest time of the day, i.e. 10-11 am. Serum prolactin levels do not vary significantly with the menstrual cycle; therefore, there is no special requirement that blood must be drawn on the first day of menstruation. Mental status at the time of blood sampling: Stressful situations such as nervousness, cold, and strenuous exercise can lead to a several-fold increase in prolactin levels, but not for more than 1 h. Therefore, the patient should be asked to be quiet for one hour before blood collection. In healthy women, stimulation of the breast during non-lactating conditions can also lead to an increase in prolactin levels. Prolactin secretion changes under physiological conditions It is normal for the body to have certain fluctuations in prolactin during physiological conditions. As the body grows and develops, prolactin levels rise mildly during puberty to adult levels, and gradually decrease by 50% over the 18 months following menopause. Prolactin does not change significantly during the menstrual cycle. It changes more during pregnancy and during postpartum lactation. Increased estrogen levels during pregnancy stimulate the pituitary gland, resulting in enlargement and increased secretion of prolactin. Prolactin gradually increases, and at the end of pregnancy, serum prolactin levels can rise up to 10 times higher than during non-pregnancy. After delivery, the enlarged pituitary gland returns to its normal size and serum lactogen levels decline. If you do not breastfeed after delivery, your serum lactogen levels will drop to normal 4 weeks after delivery; if you do breastfeed, your pituitary gland will secrete lactogen when your nipples are sucked, which will keep your serum lactogen at a high level. If strict breastfeeding is maintained after delivery, basal lactogen levels will remain elevated and postpartum amenorrhea may occur. In healthy women, stimulation of the breast during non-breastfeeding can also lead to an increase in prolactin levels. What is a prolactin adenoma Current research suggests that the most important clinical cause of HPRL is a pituitary prolactin adenoma. Prolactin adenomas are the most common functional pituitary adenomas, accounting for approximately 45% of all pituitary adenomas. Current research suggests that most prolactin adenomas are benign tumors and can be classified as microadenomas (tumors ≤ 10 mm in diameter) or macroadenomas (tumors > 10 mm in diameter) based on their diameter. Clinically, when serum prolactin level is mildly elevated without other clear etiology or serum prolactin level > 4.55 nmol/L (> 100ng/ml), imaging examination (MRI or CT) of the saddle area should be performed to determine whether there are intracranial tumors that compress the pituitary stalk or secrete prolactin and empty saddle syndrome, etc. Although it is said that when prolactin is high to a certain level, prolactin adenoma needs to be alerted, it does not mean that the degree of elevated prolactin is directly related to the size of pituitary tumor.