Test Directory

Pituitary function test useful in the differential diagnosis of Cushing syndrome, ectopic ACTH syndrome (eg, carcinoma of lung, islet cell tumors, carcinoid tumors, medullary carcinoma of thyroid), Addison disease, hypopituitarism, and ACTH-producing pituitary tumors (eg, Nelson syndrome).

Specimen Type: Plasma

Collection Container: Prechilled Lavender Top (EDTA)

Desired Specimen Volume: 0.8 mL

1. Collect a prechilled lavender top (EDTA) tube via venipuncture.
2. After venipuncture, immediately immerse the tubes in an ice bath until processing.
3. ACTH should be drawn between 7 a.m. and 10 a.m.

1. Separate plasma from cells immediately after venipuncture.
2. Transfer 0.8 mL of plasma to a LabCorp PP transpak frozen purple tube.
3. Freeze immediately and maintain frozen until tested. 
4. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.

ACTH should be drawn between 7 AM and 10 AM.

This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.

Transport to the laboratory frozen. 

• Thawed specimen
• Serum or heparinized plasma specimen
• Specimen collected in nonsiliconized glass tube

See patient report.

ACTH secretion is pulsatile so multiple specimen collections may be required. Collection in nonsiliconized tubes can result in falsely low results as ACTH adheres to glass.

As with all tests containing monoclonal mouse antibodies, erroneous findings may be obtained from samples taken from patients who have been treated with monoclonal mouse antibodies or who have received them for diagnostic purposes. In rare cases, interference due to extremely high titers of antibodies to streptavidin and ruthenium can occur. The test contains additives, which minimize these effects.

A specimen collected outside of the 7:00-10:00 AM window is not a cause for rejection. However, the reference interval is determined based on specimens collected within that timeframe. Therefore, clinical interpretation of the result will be challenging.