Samples for ionised calcium testing must be handled appropriately prior to submission in order to ensure they remain suitable for testing on receipt in the laboratory. If the samples do not meet all the criteria stipulated below, they will be unsuitable for analysis.
Specimen: Serum
Container: Plain red top tube
Minimum sample volume: 1.3mL mini tube, must be full.
Collection protocol: Vacutainer tubes must be filled to the very top. Preferably fill vacutainers using a syringe and needle. If a tube lid is removed, this must be replaced as soon as possible to reduce exposure to air (samples must be kept anaerobic).
Special handling/shipping requirements: Allow sample to clot at room temperature for minimum of 30 minutes before refrigerating. Do not centrifuge sample. Transport to laboratory chilled, on the same day as collection (chilled sample only, no direct ice contact with sample) .
Note: If samples are not clotted prior to refrigerating, free calcium becomes sequestered in the clot and will result in lowered values.
Notes for interpretation of results: Free ionised calcium testing requires strict adherence to collection and storage requirements for accuracy. If not tested immediately after collection, storage time and temperature, and any exposure to air can affect the pH of the sample which significantly affects the result. Storage at room temperature or refrigerated usually results in falling pH over time which increases ionized calcium values. Freezing and exposure to air results in increased pH and reduced ionised calcium values.
If you have any questions regarding sample collection for ionised calcium, please just give your local laboratory a call and they will be happy to help you out.