Which of the following additives is preferred when drawing blood samples to measure parathyroid hormone (PTH)?
◦ Sodium citrate because PTH is most stable using this additive
◦ Acid citrate dextrose because PTH is least stable using this additive
◦ Potassium (3)-EDTA (K3-EDTA) because PTH is most stable using this additive
◦ Sodium fluoride/potassium oxalate because PTH will complex with oxalate to increase its stability