Stability of ionized calcium measurements at concentrations less than 0.3 mmol/L by point-of-care blood gas instruments: application for postfilter calcium quality control in patients with citrate anticoagulation during extracorporeal circulation.
Background Measurements of ionized calcium (Ca2+) at concentrations less than 0.3 mmol/L are required for postfilter control in patients who receive extracorporeal circulation with sodium citrate anticoagulation. This study evaluates the stability of the Ca2+measurements at such concentrations. Methods The stability of the Ca2+measurements was tested by measuring daily the external standard Qualicheck concentration 3 s7950, Radiometer (0.22-0.25 mmol/L) by blood gas instruments ABL800 and ABL90, Radiometer. Two different Ca2+membrane lots were tested for the usual membrane lifetime of 12 weeks at ABL800 instruments. For the ABL90 instrument, the sensor cassette (with Ca2+membrane and electrode) was replaced after four weeks as required. Results We observed over 40% Ca2+increase within the usual 12 weeks lifetime of the Ca2+membrane at the ABL800 instruments. Measurements of Ca2+at concentrations less than 0.3 mmol/L were within acceptable limits for both ABL800 and ABL90 instruments when Ca2+membrane and sensor cassette were replaced after four weeks. Conclusions For ABL800 instruments, it is necessary to use an extra quality control (<0.3 mmol/L) in addition to the usual quality controls to monitor Ca2+measurements below 0.3 mmol/L. The acceptable stability of the Ca2+measurements can be achieved by the Ca2+membrane and sensor cassette replacement after four weeks. If the usual 12 weeks of Ca2+membrane lifetime is maintained, it may result in a clinically significant overestimation of Ca2+by ABL800 instruments.
1 Department of Laboratory Medicine, University Hospital of North Norway, Tromsø, Norway.|2 Institute of Medical Biology, UiT The Arctic University of Norway, Tromsø, Norway.
Maria
M
Averina
1 Department of Laboratory Medicine, University Hospital of North Norway, Tromsø, Norway.
Raymond
R
Jakobsen
D000925:Anticoagulants / Q000737:chemistry*; D016477:Artifacts; D001784:Blood Gas Analysis / Q000592:standards*; D002118:Calcium / Q000097:blood*; D002413:Cations, Divalent; D002951:Citrates / Q000737:chemistry*; D005112:Extracorporeal Circulation / Q000295:instrumentation; D006801:Humans; D008567:Membranes, Artificial; D019095:Point-of-Care Systems; D000067716:Point-of-Care Testing / Q000592:standards*; D011786:Quality Control; D015203:Reproducibility of Results; D000077559:Sodium Citrate; D013997:Time Factors
D000925:Anticoagulants; D002413:Cations, Divalent; D002951:Citrates; D008567:Membranes, Artificial; D000077559:Sodium Citrate; D002118:Calcium
Calcium; ion-selective electrodes; quality assurance and control