Draw a SST (gel- barrier) or Red Top tube and; Allow blood to clot for 1-4 hours in an ice bath or refrigerator (2 degrees C to 8 degrees C). Spin in chilled centrifuge holders or refrigerated centrifuge. Transfer the serum into a plastic transport tube and freeze. The specimen should be FROZEN immediately and maintained FROZEN until tested. DO NOT ALLOW TO THAW IN TRANSPORT. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested. State on the request form if calcium infusion or pentagastrin injection tests are part of the patient preparation.