Abstract
Aims: Urease-producing microorganisms may lower urea nitrogen (UN) during dialysate-side dosing. We investigated the impact of 3 proven preservatives (acetic acid, ceftazidime, thimerosal) on UN concentration, and the concentrations of creatinine (CR) and β<sub>2</sub>-microglobulin (β<sub>2</sub>M). Methods: The UN, CR and β<sub>2</sub>M concentrations were assayed in 3 separate aliquots from 20 spent dialysate samples (ceftazidime, 125 mg/l, or 1% thimerosal, 1 ml/l, vs. control). The β<sub>2</sub>M concentration was assayed in 10 further spent dialysate collections (concentrated glacial acetic acid, 5 ml/l, vs. control). Solute concentrations were compared with the concordance correlation coefficient (r<sub>c</sub>). Results: Ceftazidime and thimerosal had little effect on the concentrations of UN and CR (r<sub>c</sub> >0.97). For the β<sub>2</sub>M concentration, agreement remained good (r<sub>c</sub> >0.96) for ceftazidime and thimerosal (although the former tended to lower concentrations) but acetic acid was less optimal (r<sub>c</sub> = 0.893). Conclusions: Ceftazidime and thimerosal may be used as dialysate preservatives without affecting the UN or CR concentrations. Thimerosal is to be preferred when studying β<sub>2</sub>M. Acetic acid produces unacceptable inaccuracy when measuring β<sub>2</sub>M.
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