Right time to detect urine iodine during papillary thyroid carcinoma diagnosis and treatment: A case report

This is the first documentation of a spontaneous and nonspecific chemical reaction of an iodinated contrast media with ammonium persulfate used in As³⁺-Ce⁴⁺ catalytic spectrophotometry for urine iodine concentration (UIC) detection.

We herein report an incidental case who had a dual source computed tomography examination for papillary thyroid carcinoma diagnosis. Serial spot urine specimens were collected during her hospitalization and were measured by As³⁺-Ce⁴⁺ catalytic spectrophotometry on a Beckman Coulter AU5800. The reacted solutions were "brownish", and the results showed extremely high iodine concentrations despite serial dilutions. The patient claimed no dietary habit of iodized salt or iodine-containing medical history, which strongly pointed to iodinated contrast media (ICM) via intravenous injection. Even with 0.01% ICM, its interruption is still profound on the desired urine iodine reaction with ammonium persulfate, leading to inaccurate UIC and possibly inappropriate treatment.

The following laboratory suggestions should be considered: (1) As³⁺-Ce⁴⁺ catalytic spectrophotometry is only suitable for UIC measurement after confirmed ICM renal clearance; (2) A mass spectrometry-based method can be applied as an alternative during the ICM clearance period; and (3) The UIC baseline can be confirmed after ICM injection by consecutive detection for at least 2 mo.