Objective: To determine the effect of commercially available arterial
blood sampling devices on ionized calcium measurements. Design: Prospe
ctive study. Setting: Neurosurgical and shock-trauma intensive care un
its (ICU) at a tertiary care teaching hospital. Patients: Fourteen pat
ients admitted to the ICU, Each patient had an indwelling arterial cat
heter. Interventions: Arterial blood sampling, Measurements and Main R
esults: In 14 ICU patients, measurements of arterial blood ionized cal
cium concentrations were performed, using 12 different commercially av
ailable arterial blood sampling devices. Significant underestimation o
f ionized calcium in blood samples compared with the reference test tu
be (Vacutainer 45) was seen in seven of the devices. Arterial blood io
nized calcium concentrations measured, using one commercially availabl
e syringe, were significantly higher compared with the reference test
tube. There was no correlation between either the amount or type of he
parin in the arterial blood sampling devices and arterial blood ionize
d calcium measurement. Conclusions: This study demonstrates that vario
us commercially available arterial blood sampling devices alter arteri
al blood ionized calcium measurements, These alterations are clinicall
y important because ICU patients may be treated with inappropriate cal
cium supplementation.