Falsely High Prolactin level: A Diagnostic Pitfalls

Prolactin (PRL) is a hormone produced by the pituitary gland in the brain that plays a role in lactation and reproduction.  The elevation of serum PRL levels (hyperprolactinemia) has multiple etiologies that can be divided into physiological, pharmacological, and pathological causes. 

There are several potential reasons for a falsely high prolactin level in a blood sample. Prolactin levels of women were significantly higher in the morning than those in the evening. Prolactin is secreted in a circadian and pulsatile pattern. Serum prolactin level reaches its maximum in the early morning hours, returns to the normal value one hour after waking up, and is lower in the evening than that in the morning. Prolactin is often measured in the early morning hours along with other tests that require fasting and is affected by the physiological morning peak. So, it can be falsely higher than the normal range and can lead to further unnecessary investigations. 

Certain medications can falsely increase prolactin levels. For example, antipsychotic medications, some antidepressants, anti-hypertensive drugs, and acid-reducing medications, can also potentially cause elevated prolactin levels.

Underactive thyroid gland (hypothyroidism) can disrupt the hormonal balance in the body, leading to elevated prolactin levels.

Intense physical activity or emotional stress just prior to blood collection can stimulate the release of prolactin, leading to a falsely high result. It's important to be in a relaxed state during blood collection to minimize the risk of stress-induced prolactin elevation.

Recent sexual activity or nipple stimulation can cause a temporary increase in prolactin levels. Therefore, blood samples taken shortly after sexual activity or nipple stimulation may yield a falsely high prolactin level.

It is recognized that a substantial proportion of patients found to have raised prolactin (PRL) level on a single testing is subsequently found to have normal PRL levels. Though this is often attributed to stress or medication factor, it should be noted, that PRL secretion displays diurnal variation. It is recommended that screening for hyperprolactinemia includes three specimens be obtained at 20- to 30-minute intervals in mid-morning. Each sample can either be analyzed separately or be pooled into a single specimen. When a drug-induced rise in PRL is suspected, PRL sampling should be repeated after withdrawal of medications for at least 72 h, if possibile. 

It's important to note that a single blood test indicating high prolactin levels may not be enough for a definitive diagnosis. Further evaluation, including medical history, physical examination, and additional testing, may be necessary to determine the underlying cause of hyperprolactinemia.