From the Guidelines
The laboratory workup for a pituitary tumor should include a comprehensive panel of hormone tests, with a strong emphasis on performing serial dilutions of serum for prolactin measurement in cases with large pituitary lesions and normal or mildly elevated prolactin levels. This approach is crucial for accurately diagnosing and managing pituitary adenomas, as highlighted in a recent consensus guideline published in Nature Reviews Endocrinology 1. The guideline recommends serial dilutions for prolactin measurement to avoid the "high-dose hook effect," which can lead to artificially low measurements of prolactin levels.
When evaluating a pituitary tumor, the initial testing should include:
- Prolactin levels, with consideration for serial dilutions as needed
- IGF-1
- Morning cortisol
- ACTH
- TSH
- Free T4
- LH
- FSH
- Testosterone (in men) or estradiol (in women)
- Growth hormone
Additional testing may be necessary based on clinical suspicion, such as:
- 24-hour urinary free cortisol test, overnight dexamethasone suppression test, and late-night salivary cortisol for suspected Cushing's disease
- Oral glucose tolerance test with growth hormone measurements for acromegaly
- Serum and urine osmolality and sodium levels for diabetes insipidus
It is essential to note that the specific pattern of hormone abnormalities can help localize the lesion to the pituitary and guide treatment decisions. As recommended by a recent consensus guideline, testing for GH excess should be offered to children and young people with excess height or consistently elevated height velocity and acromegalic features 1. Regular follow-up testing should be scheduled to monitor treatment response and detect any changes in pituitary function.
From the Research
Pituitary Tumour Lab Work Up
- Pituitary tumors can cause an excess or deficiency of anterior pituitary hormones, including growth hormone (GH), adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), and prolactin (PRL) 2
- Comprehensive preoperative endocrine evaluation is essential for appropriate therapeutic decision-making and safe surgery, and may include endocrine function tests and intravascular catheterization for inferior petrosal sinus sampling for pituitary tumors 2
- Lab work up for pituitary tumors may include measurement of serum hormone levels, such as TSH, free T4, free T3, prolactin, GH, ACTH, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) 3, 4
- Reference ranges for these hormones can vary between laboratories, and may be influenced by factors such as age, sex, and medical history 4
- In some cases, pituitary tumors may coexist with other endocrine disorders, such as autoimmune hypothyroidism, and lab work up may need to take this into account 3
- The diagnosis and evaluation of pituitary tumors may also involve imaging studies, such as MRI scans, and other diagnostic tests, such as inferior petrosal sinus sampling 2, 3
- Some studies have investigated the relationship between pituitary tumors and other cancers, such as differentiated thyroid cancer, and found that patients with prolactinoma may be at increased risk of developing thyroid cancer 5
- Serotonin has been shown to have a direct action on pituitary secretion, stimulating the release of PRL, GH, ACTH, and LH, and may play a role in the development of pituitary tumors 6