Hello Caitlin! According to the U.S. Department of Health and Human Services (2009), here are the following specimen considerations:

• No special instructions such as fasting or special diets are required. Diurnal variation is not a major consideration.
• Specimens may be serum, recalcified plasma, or plasma. Serum specimens may be collected using regular red-top or serum-separator Vacutainers.
• The required sample volume is 10 μL for the assay; 1.0 mL will permit repeat analyses as well as other testing.
• Specimens should be stored in plastic vials and sealed tightly to prevent desiccation of the sample.
• Serum or plasma samples are collected aseptically to minimize hemolysis and bacterial contamination.
• Samples are stored in labeled 2 mL Nalgene cryovials or equivalent.
• The serum is best stored frozen, and freeze/thaw cycles should be kept to a minimum. Store samples at 4-8°C for no more than 5 days.
• For storage >5 days, samples are held at -20°C. Samples held in long-term storage at -20°C are indexed in the database for easy retrieval.
• Specimens are rejected if contaminated, hemolyzed, or stored improperly. However, rejection is done only after consultation with NCHS.
• Avoid multiple freeze/thaw cycles.

References:

U.S. Department of Health and Human Services. (2009). Biosafety in Microbiological and Biomedical Laboratories (5th ed.) [E-book]. HHS Publication No. (CDC) 21-1112. https://www.cdc.gov/labs/pdf/CDC-BiosafetymicrobiologicalBiomedicalLaboratories-2009-P.pdf