MEDVAC® Citrate Tubes(9NC 0.109M)/(9NC 0.129M) are generally used for coagulation studies. The tubes contain buffered sodium citrate solution as an anticoagulant. Citrate concentration of either 0.109M (3.2 %) or 0.129M (3.8 %) is available. The mixing ratio is 1 part citrate to 9 parts blood.