Discrepant post filter ionized calcium concentrations by common blood gas analyzers in CRRT using regional citrate anticoagulation.
BACKGROUND
Ionized calcium (iCa) concentration is often used in critical care and measured using blood gas analyzers at the point of care. Controlling and adjusting regional citrate anticoagulation (RCA) for continuous renal replacement therapy (CRRT) involves measuring the iCa concentration in two samples: systemic with physiological iCa concentrations and post filter samples with very low iCa concentrations. However, modern blood gas analyzers are optimized for physiological iCa concentrations which might make them less suitable for measuring low iCa in blood with a high concentration of citrate. We present results of iCa measurements from six different blood gas analyzers and the impact on clinical decisions based on the recommendations of the dialysis' device manufacturer.


METHODS
The iCa concentrations of systemic and post filter samples were measured using six distinct, frequently used blood gas analyzers. We obtained iCa results of 74 systemic and 84 post filter samples from patients undergoing RCA for CRRT at the University Medicine of Greifswald.


RESULTS
The systemic samples showed concordant results on all analyzers with median iCa concentrations ranging from 1.07 to 1.16 mmol/L. The medians of iCa concentrations for post filter samples ranged from 0.21 to 0.50 mmol/L. Results of >70% of the post filter samples would lead to major differences in decisions regarding citrate flow depending on the instrument used.


CONCLUSIONS
Measurements of iCa in post filter samples may give misleading information in monitoring the RCA. Recommendations of the dialysis manufacturer need to be revised. Meanwhile, little weight should be given to post filter iCa. Reference methods for low iCa in whole blood containing citrate should be established.
Institute of Clinical Chemistry and Laboratory Medicine, University Medicine Greifswald, Ferdinand-Sauerbruch-Strasse, 17475, Greifswald, Germany. patrik.schwarzer@outlook.de.
Patrik
P
Schwarzer
Department of Anaesthesiology and Intensive Care Medicine, University Medicine Greifswald, Greifswald, Germany. kuhn@uni-greifswald.de.
Sven-Olaf
SO
Kuhn
Department of Internal Medicine A, University Medicine Greifswald, Greifswald, Germany. sylvia.stracke@uni-greifswald.de.
Sylvia
S
Stracke
Department of Anaesthesiology and Intensive Care Medicine, University Medicine Greifswald, Greifswald, Germany. gruendli@uni-greifswald.de.
Matthias
M
Gründling
Department of Anaesthesiology and Intensive Care Medicine, University Medicine Greifswald, Greifswald, Germany. stephan.knigge@uni-greifswald.de.
Stephan
S
Knigge
Department of Anaesthesiology and Intensive Care Medicine, University Medicine Greifswald, Greifswald, Germany. sixten.selleng@uni-greifswald.de.
Sixten
S
Selleng
Institute of Clinical Chemistry and Laboratory Medicine, University Medicine Greifswald, Ferdinand-Sauerbruch-Strasse, 17475, Greifswald, Germany. mhelm1994@googlemail.com.
Maximilian
M
Helm
Department of Internal Medicine B, University Medicine Greifswald, Greifswald, Germany. frieseck@uni-greifswald.de.
Sigrun
S
Friesecke
Department of Internal Medicine B, University Medicine Greifswald, Greifswald, Germany. abel@uni-greifswald.de.
Peter
P
Abel
Karolinska University Hospital, Stockholm, Sweden. Anders.Kallner@ki.se.
Anders
A
Kallner
Institute of Clinical Chemistry and Laboratory Medicine, University Medicine Greifswald, Ferdinand-Sauerbruch-Strasse, 17475, Greifswald, Germany. matthias.nauck@uni-greifswald.de.
Matthias
M
Nauck
Institute of Clinical Chemistry and Laboratory Medicine, University Medicine Greifswald, Ferdinand-Sauerbruch-Strasse, 17475, Greifswald, Germany. astrid.petersmann@uni-greifswald.de.
Astrid
A
Petersmann
D000925:Anticoagulants / Q000627:therapeutic use*; D001784:Blood Gas Analysis / Q000295:instrumentation / Q000379:methods; D002118:Calcium / Q000097:blood*; D002951:Citrates / Q000627:therapeutic use*; D005188:False Negative Reactions; D005189:False Positive Reactions; D006440:Hemofiltration / Q000379:methods*; D006801:Humans; D015203:Reproducibility of Results
D000925:Anticoagulants; D002951:Citrates; D002118:Calcium