Collection Information: PARTIAL draw tubes are not acceptable for ionized calcium testing. If a tourniquet is used, it must be left on until all the required blood is drawn (but no longer than 3 minutes), and patient should not be allowed to exercise the forearm. The patient must avoid strenuous activity immediately before phlebotomy. Avoid fist clenching during phlebotomy.

Blood collection from central venous catheter lines and dialysis catheters are not recommended and MUST be avoided if locking solutions containing anticoagulant agents such as Heparin (>100 U/ml) or Sodium Citrate (4%) as they can bind to calcium ions with great affinity and will lead to falsely lower ionized calcium measurement. Total calcium level however will be unaffected from these anti-coagulant agents.

Special Processing: Centrifuge samples within 2 hours of collection. Do not remove stopper. If sample cannot be analyzed immediately, it can be stored anaerobically at 4 C for up to 48 hours.
Samples in microtainers should be analyzed immediately
Micro collection procedure:
a) Warm foot. b) Perform skin puncture. c) Keeping foot lower than the heart, and with minimal squeezing, fill microtainer completely, cap and transport to lab without delay.  Analyze immediately.