Peripheral vein and fistula blood samples after single-needle dialysis

It is traditional in renal units to check patients' biochemical parameters pre- and postdialysis. When a single-needle system is used, the blood is obtained through the arterial limb of the Y cannula, thus avoiding an extra venipuncture. The pre-sample is taken immediately after the cannula is inserted and the post-sample is taken after the blood lines have been disconnected and the venous limb clamped. It was the purpose of this investigation to determine whether the post-samples gave an accurate indication of the patient's electrolyte status. Samples taken from the arteriovenous fistula and those taken simultaneously from a peripheral vein in the opposite arm were compared. It is concluded that postdialysis concentrations should be determined from peripheral vein samples only.