Self-prepared heparinized syringes for measuring ionized magnesium in critical care patients

We have compared ionized magnesium assays in the Nova 8 electrolyte analyse r using dry balanced heparinized syringes and self-prepared heparinized syr inges. Thirty blood specimens were obtained into syringes either operator-p repared with liquid sodium heparin or commercially manufactured dry balance d heparinized syringes. There was a good correlation between results from t he two syringes. The mean difference between sampling methods was 0.01 mmol litre(-1) (95% confidence index -0.05 to 0.08 mmol litre(-1)). The correla tions for sodium, potassium and ionized calcium assays were similarly close . The relationship between sampling methods was close enough to justify the clinical use of self-prepared syringes, with potential economies in clinic al costs.