SPURIOUS RISE IN TOTAL CARBON-DIOXIDE AND CHLORIDE WITH NEGATIVE ANION GAP AFTER CYSTOGRAM

We report a case of spurious hyperchloraemia, elevated total carbon di oxide and negative anion gap 9 days following a voiding cystourethrogr am (VCU) in a patient with bladder exstrophy and obstructive uropathy. We believe that the spurious laboratory results were due to analytica l interference of the absorbed iodine with the method of bicarbonate a nd chloride measurement. The absorbed iodine was retained in the circu lation for an extended period because of associated renal impairment. Our patient was also on piperacillin which might have interfered with iodine clearance. Physicians and laboratory pathologists should be awa re of this effect when interpreting laboratory results of patients who have undergone a VCU in association with obstructive uropathy and imp aired renal function.