Chromatographic Identification in Serum of Endogenously Radioiodinated Thyroid Hormones After Iodine-131 Whole-Body Scintigraphy in the Follow-up of Patients with Differentiated Thyroid Carcinoma

Patients wfthdifferentiatedthyroid cancer (DTC)are convention allyfollowed withsedal1311 whole-body Santigraphy (WBS) and serum thyrogiobulin(hTg)assay. Giventhe I 5%-20% incidence of discordantresufts,we developeda sensitiveand specific procedurefor monitoring such patients,based on the assump tionthat 1311 uptake,even iftoo lowtobe detectedby 1311 WBS, couldbe assayed inserumas thyrokiproducts(hTg,T3and TJ endogenouslylabeledwith1311. Ourstudyincluded125patients routinelymonitored fortumorrecurrenceorforthe persistenceof functioningthyroidtissue after completepnrnaiyfreatmentfor DTC(surgery and1311 ablation of remnants). A plasmasample, taken 72 hr afteradministering 1311 forWBSwas fractionatedon a Sephadex-G25superfinecolumnby firstelutingall of the radioactivespecies except the thyroidhormonesand then the radioiodothyronines. The sensffivfty and specificityof chroma tography in detecting functioningthyroidtissue after pnmary treatment for DTC were 98.4% and 100% (accuracy 99.2%), respectively,versus 90.6%and 95.1%for 1311 WBS(accuracy 92.8%)and60.9%and100%forhTg(accuracy 80%).Combin ing chromatography w@i serum hTg gave the highest gains in disgnosticperformance(100%for all parameters).This chro matographicmethod can be used in additionto conventional proceduresinthe follow-up of patientswithDTCand represents a highly sensitivetestforassessingtheresuttsof 1311 ablation of postsurgicalremnants. J NuciMed1993;34:2032-2037