A blood test gave a falsely low reading in a woman with a giant pituitary tumor
Original title: Hyperprolactinaemia masked by the hook effect in a patient with a giant prolactinoma with growth hormone co-secretion.
How far along is this research?
- Lab cells
- Animals
- Review
- Tested in people
This was tested in people. That is the most reliable kind of research we share.
The lab test and the medicines described here are already approved and used in care today.
The short version
A large pituitary tumor can trick a hormone blood test into reading much lower than the truth, and a repeat test done a different way found the real level.
What was studied. This is a report about one woman in her 50s. She had a giant tumor at the base of the skull, in the pituitary gland, that made two hormones, prolactin and growth hormone. She had headaches, bulging and swollen eyes, and her periods had stopped since her 20s. Doctors describe her hormone tests and the medicines she was given.
What they found. Her first prolactin test read 251 µg/L, when normal is 23 µg/L or less. The lab then diluted her blood sample and tested it again. This time the level was 386 020 µg/L. She was treated with cabergoline and got much better, and both the tumor and her prolactin level went down. A drug called lanreotide did not help her growth hormone, so she was switched to pegvisomant, and a growth hormone marker in her blood returned to normal.
What this means, and what it doesn't
What it could mean: If you have a large pituitary tumor, a prolactin result that looks only mildly high may not be the full picture. It can help to ask your doctor whether the sample should be diluted and run again. Getting the true number matters, because it can change the diagnosis and the treatment plan.
What it doesn't mean: This is one person's story, not a study. One case cannot show how well any of these medicines work for other people. These drugs are already in use, but they are not a cure, and they do not work the same way for everyone. This report is a caution for doctors about a lab test problem, not a new treatment. The doctors also warn that this type of medicine should be increased slowly in people with large tumors, because of serious risks.
Source: PubMed, July 13, 2026 · Read the original
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