1 mL serum.
Ship in insulated container with freezer packs.
Do not use SST blood collection tubes. Collect blood into a red-top vacutainer; avoid hemolysis. Separate serum from cells as soon as possible following collection and transfer to a leakproof tube. Refrigerate until shipped.
Free T4 by equilibrium dialysis run weekly. See Clinical Pathology section-hyperthyroidism *& hypothyroidism * of the User's Guide.