Somatostatin 

Updated: May 16, 2022
  • Author: Cory Wilczynski, MD; Chief Editor: Sridevi Devaraj, PhD, DABCC, FAACC, FRSC, CCRP  more...
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Reference Range

Somatostatin is a polypeptide that is released in the gastrointestinal tract by delta cells and the hypothalamus. It functions as a key regulatory peptide that has many physiologic effects as an inhibitor for many other hormones, including gastrin, cholecystokinin, glucagon, growth hormone, insulin, secretin, pancreatic polypeptide, vasoactive intestinal peptide, 5-hydroxytryptamine (5-HT), and some anterior pituitary hormones.

The reference range for plasma somatostatin in adults is 10-22 pg/mL, the conversion factor is 0.426, and the SI units are 4.26-9.37 pmol/L. Draw in prechilled tube, separate plasma, and freeze immediately. [1]

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Background/Interpretation

Serum and cerebrospinal fluid (CSF) somatostatin values less than 100 pg/mL are within normal limits for healthy individuals. Decreased levels have been found to be seen in CSF in autopsy samples of people with Alzheimer disease. [2] No change was found in normal, younger subjects to suggest that this could be a predisposing laboratory screen for dementia patients. CSF values were also found to be elevated in young patients with febrile seizures. [3] Elevations in serum somatostatin are seen in somatostatinomas and neuroendocrine tumors. [4, 5] The levels are found to be on the scale of nanograms per milliliter, which is nearly 1000-fold greater than the standard unit. These tumors are very rare and slow-growing, but most patients are symptomatic. The following is the classic pentad of symptoms seen in a somatostatinoma syndrome: [6]

  • Cholelithiasis

  • Weight loss

  • Steatorrhea and diarrhea

  • Hypochlorhydria and achlorhydria

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Collection and Panels

Serum somatostatin

See the list below:

  • Specimen: Plasma

  • Condition: Fasting

  • Container: Lavender (EDTA; see image below) or pink (K2 EDTA) pre-chilled tube

    Lavender-top tube. Lavender-top tube.
  • Collection method: Routine venipuncture

  • Processing: Separate plasma from cells within 2 hours of collection in lab; an adequate sample requires a minimum of 0.6-1.8 mL. If multiple samples need to be analyzed, the specimen should be kept frozen. Ambient temperatures and exposure to room air will make sample unacceptable for analysis. [7]

Cerebrospinal fluid somatostatin

See the list below:

  • Specimen: CSF

  • Collection method: Lumbar puncture

  • Typically part of same panel as CSF cell count, gram stain, albumin, glucose

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Background

Somatostatin is a polypeptide that is released in the gastrointestinal tract by delta cells and the hypothalamus. It functions as a key regulatory peptide that has many physiologic effects as an inhibitor for many other hormones, including gastrin, cholecystokinin, glucagon, growth hormone, insulin, secretin, pancreatic polypeptide, vasoactive intestinal peptide, 5-HT, and some anterior pituitary hormones.

Because intravenously injected somatostatin has a short half-life in the circulation (3 minutes), it has limited clinical usefulness. [8] Therefore, synthetic preparations, including octreotide and lanreotide, that mimic the properties of somatostatin are used. Octreotide is an octapeptide that can be given intravenously (30 min), subcutaneously (6-12 hours), or intramuscularly (monthly) for various applications. The most common indications for use include imaging for somatostatinomas, other neuroendocrine tumors, variceal bleeding, refractory diarrhea, and hypoglycemia. [8]

Lanreotide injection is used as long-term treatment for patients with acromegaly in whom surgery and/or radiotherapy have led to an inadequate response or are not an option. It is also employed to improve progression-free survival in patients with unresectable, well- or moderately differentiated, locally advanced or metastatic gastroenteropancreatic neuroendocrine tumors. [9]

A study by Benderradji et al found that in patients with newly diagnosed acromegaly caused by pituitary macroadenomas, who had optic chiasm compression (grade 2 or below) and/or cavernous sinus invasion, primary therapy with monthly injections of lanreotide 120 mg led to a significant reduction in somatotroph macroadenoma size at 1 month. More specifically, volume reduction was 25% or greater in 61.9% of individuals at 1 month, while half of those patients with optic chiasm compression and visual field defects experienced visual field normalization or improvement at 1 month. [10]

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