What is the role of lab studies in the diagnosis of carcinoid tumor?

Updated: Feb 12, 2019
  • Author: Cameron K Tebbi, MD; Chief Editor: Max J Coppes, MD, PhD, MBA  more...
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Laboratory diagnosis of carcinoid tumors depends on the identification of the characteristic biomarkers of the disease. Measurement of biogenic amines levels (eg, serotonin, 5-HT, catecholamines, histamine) and its metabolites in the platelets, plasma, and urine of patients can be helpful in diagnosis.

  • Urinary 5-HIAA levels are usually increased and aid in the assessment of carcinoid tumors. [70, 71, 72, 73, 74, 75] Measurement of urinary 5-HIAA levels can help in diagnosing carcinoid syndrome but may not help in detecting tumors at an early stage of development when they are potentially curable with resection. Although the detection of urinary 5-HIAA is the single best screening method for carcinoid tumors, the level is not always elevated, and the measurement of other peptides (eg, SP, neuropeptide K, chromogranin) may be necessary for diagnosis and follow-up.

  • Fasting plasma 5-HIAA assay is more stable than whole-blood serotonin assay and is more convenient than 24-hour urine collection. [76] Substances produced by carcinoid tumors are listed in Pathophysiology above.

  • In one study, CDX2 was highly indicative of GI carcinoid tumor, whereas TTF-1 had high specificity for pulmonary tumors. [77] One (17%) of 6 gastric carcinoids stained with CDX2, whereas 8 (53%) of 15 pulmonary carcinoids stained with TTF-1. None of the GI tumors stained with TTF-1.

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