Fill a citrate (light blue top) tube as far as vacuum will allow and mix by gentle inversion five to six times. The exact ratio of 1 part sodium citrate to 9 parts blood must be maintained. Inadequate filling of the sample tube will alter this ratio and may lead to inaccurate results. Centrifuge sample and separate plasma from cells immediately. Transfer plasma to a plastic transport tube. Clearly label tube as citrate plasma. Freeze. Critical Frozen (CFZ). When multiple tests are ordered, submit separate tube for this test.