Serotonin, Whole Blood (Sendout)

Interpretation

Method

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Reference Range

Units: ng/mL

Female		Male
Age	Range	Age	Range
0-	0-330	0-	0-330

Effective date: 02/17/2007

Ref. Range Notes

Interpretation:

Metastasizing midgut carcinoid tumors usually produce blood or serum serotonin (5-hydroxytryptamine) concentrations greater than 1000 ng/mL. However, elevations above 400 ng/mL are suggestive of carcinoid tumors as the cause of carcinoid syndrome-like symptoms. Lesser increases may be nonspecific or drug-related (see Limitations).

Only a minority of patients with carcinoid tumors will have elevated serotonin levels. It is usually impossible to diagnose small carcinoid tumors (>95% of cases) without any symptoms suggestive of carcinoid syndrome by measurement of serotonin, 5-hydroxyindoleacetic acid (5-HIAA), or chromogranin A.

In patients with more advanced tumors, circulating serotonin is elevated in nearly all patients with midgut tumors, but only in approximately 50% of those with foregut carcinoids, and in no more than 20% of individuals with hindgut tumors. Foregut and hindgut tumors often have low or absent 5-hydroxytryptophan (5-HTP) decarboxylase activity and, therefore, may produce little if any serotonin. Urinary 5-HIAA is elevated in almost all carcinoid-syndrome patients with midgut tumors, in about 30% of individuals with foregut carcinoids, but almost never in hindgut tumors. Serum chromogranin A measurements are particularly suited for diagnosing hindgut tumors, being elevated in nearly all cases, even though serotonin and 5-HIAA are often normal. Chromogranin A is also elevated in 80% to 90% of patients with foregut and midgut tumors. Therefore, to achieve maximum sensitivity in the initial diagnosis of suspected carcinoid tumors, serotonin in serum/blood, 5-HIAA in urine, and serum chromogranin A should all be measured. In most cases, if none of these 3 analytes is elevated, carcinoids can be excluded as a cause of symptoms suggestive of carcinoid syndrome. For some cases, additional tests, such as urinary serotonin measurement, will be required. An example would be a non-chromogranin-secreting foregut tumor that only produces 5-HTP, rather than serotonin. In this case, circulating chromogranin, serotonin levels, and urinary 5-HIAA levels would not be elevated. However, the kidneys can convert 5-HTP to serotonin, leading to high urinary serotonin levels.

Disease progression can be monitored in patients with serotonin-producing carcinoid tumors by measurement of serotonin in blood. However, at levels above approximately 5000 ng/mL, the serotonin storage capacity of platelets becomes limiting, and there is no longer a linear relationship between tumor burden and blood serotonin levels. Urinary 5-HIAA and serum chromogranin A continue to increase in proportion to the tumor burden to much higher serotonin production levels and are, therefore, better suited for follow-up in patients with extensive disease.

Interferences and Limitations

Cautions:

Since most circulating serotonin (5-hydroxytryptamine) is contained in platelets, the preferred specimens for measurement either include all or most of the platelets (ie, whole blood and platelet-rich plasma) or consist of serum from completely clotted specimens, a process that releases nearly all serotonin from platelets. "Ordinary" or platelet-poor plasma specimens are not suitable.

Medications that may elevate serotonin concentrations include lithium, monoamine oxidase inhibitors, methyldopa, morphine, and reserpine. The observed levels are usually less than400 ng/mL. Selective serotonin reuptake inhibitors (SSRI; eg, fluoxetine) can lead to depletion of platelet serotonin levels and result in false-negative serum and blood serotonin tests. The effects of drugs are more marked on urinary serotonin and 5-hydroxyindoleacetic acid (5-HIAA) levels than on serum and blood serotonin levels.

Serotonin- or tryptophan-rich foods (eg, avocados, bananas, plums, walnuts, pineapple, eggplant, plantain, tomatoes, hickory nuts, kiwi, dates, grapefruit, cantaloupe, and honeydew melon) do not contribute significantly to serum or blood serotonin measurements, but can elevate platelet-poor plasma serotonin, urinary serotonin, and urinary 5-HIAA levels markedly (up to 10-fold).

References

• Mayo Clinical & Interpretive Information: Serotonin, Whole Blood

Ordering & Collection

Specimen Type

Whole blood

Collection

3 mL blood in LAVENDER TOP (EDTA) tube

After Collection: Transport sample to the lab immediately. Expedited processing is required.

Handling Instructions

Outside Laboratories:

• Prior to collection, obtain special aliquot: Serotonin (Ascorbic Acid) Tube (Mayo Supply T259) by contacting Client Support Services at (206) 520-4600 or commserv@uw.edu.
• Immediately after the venipuncture, transfer approximately 2.5 mL of whole blood to serotonin (ascorbic acid) tube and mix well (any volume of whole blood from 1.5-3 mL is acceptable)
• Freeze specimen without delay (necessary to lyse the RBCs).
• Specimens must be processed (whole blood transferred to serotonin/ascorbic acid tube and frozen) within 2 hours of collection.

Stability (after transfer to serotonin tube): Frozen: 90 days. Refrigerated, Ambient: Unacceptable.

Quantity

Requested: 2.5 mL EDTA whole blood in Serotonin Tube
Minimum: 1.5 mL EDTA whole blood in Serotonin Tube

Processing

Receiving Instructions

SPS: Do not centrifuge. Samples must be processed within 2 hours of collection.

• Obtain a Serotonin (Ascorbic Acid) aliquot tube [Mayo Supply T259].
• Decant in Sunquest and label the Serotonin tube with the CID aliquot label.
• Immediately deliver the whole blood sample and labeled Serotonin aliquot tube to the Chemistry Manual Bench for processing.

Chemistry:

• Transfer approximately 2.5 mL of whole blood to serotonin tube and mix well (any volume of whole blood from 1.5-3 mL is acceptable).
• Freeze sample immediately at -20°C (place in Sendouts Frozen Rack).

Sendouts:

• Order Mayo Test: SERWB
• Interfaced: Yes [Interface: 601; Worksheet: MAFZ]

Stability (after transfer to serotonin tube): Frozen: 90 days. Refrigerated, Ambient: Unacceptable.

Misc Sendout

Performance

Lab Department

Sendouts Mayo Lab (FZ)(MAFZ)

Frequency

Performed: Monday, Wednesday, Friday. Report Available: 5-8 days from sample receipt at Mayo Clinic Labs.

Available STAT?

No

Performing Location(s)

Sendout	Mayo Clinic Laboratories (Superior Drive) 800-533-1710 3050 Superior Drive NW Rochester, MN 55901

Billing & Coding

CPT Codes

84260

LOINC

2939-7

Interfaced Order Code

UOW2060

Interfaced Result Code

UOW2060