Discrepancia en concentraciones de hormonas tiroideas libres medidas por distintos inmunoensayos / Discrepancy in concentrations of free thyroid hormones measured by different immunoassays

Abstract: Thyroid function is assessed by measuring thyrotropin and free and total thyroid hormone concentrations. There are interferences with the results of immunoassays that can lead to an incorrect diagnosis, of which the most frequent are the binding of thyroid hormones to heterophile antibodies, rheumatoid factor, anti-Ruthenium antibodies, the intake of biotin and anti-streptavidin antibodies. We present three cases of clinically euthyroid patients, with normal TSH, high free T4 and T3, and normal total T4 and T3 performed in a Roche Diagnostics ® COBAS 8000 device. When the test was repeated on a Siemens® Immulite device, the free and total hormones were within normal ranges. In the Roche Diagnostics ® assay, the presence of biotin or anti-Ruthenium or anti-streptavidin antibodies interferes with the formation of the complex responsible for the emission of light that allows inferring concentrations of thyroid hormones. The Siemens test works differently since the emission of light depends on the binding of T4 to an antibody conjugated with alkaline phosphatase not participating in the process biotin, streptavidin or ruthenium so this interference is avoided. This possible interference in immunoassays should be taken into account in case clinical manifestations differ from these laboratory determinations, to avoid a diagnosis and potential inappropriate treatment.

Resumen: La función tiroidea se evalúa midiendo tirotropina y concentraciones de hormonas tiroideas libres y totales. Existen interferencias con los resultados de inmunoensayos que pueden llevar a un diagnóstico incorrecto, de ellas, las más frecuentes son la unión de hormonas tiroideas a anticuerpos heterófilos, el factor reumatoide, anticuerpos anti Rutenio, la ingesta de biotina y anticuerpos anti estreptavidina. Se presentan tres casos de pacientes clínicamente eutiroideos, con TSH normal, T4 y T3 libres elevadas, y T4 y T3 totales normales realizadas en un equipo COBAS 8000 de Roche Diagnostics®. Cuando se repitió el ensayo en un equipo Immulite de Siemens®, las hormonas libres y totales estaban dentro de rangos normales. En el ensayo de Roche Diagnostics ®, la presencia de biotina o anticuerpos anti Rutenio o anti estreptavidina, interfiere con la formación del complejo responsable de la emisión de luz que permite inferir las concentraciones de las hormonas tiroideas. El ensayo de Siemens funciona de manera diferente ya que la emisión de luz depende de la unión de la T4 a un anticuerpo conjugado con fosfatasa alcalina no participando en el proceso biotina, estreptavidina o Rutenio por lo que se evita esta interferencia. Esta posible interferencia en inmunoensayos debe ser tenida en cuenta en caso de que las manifestaciones clínicas difieran de estas determinaciones de laboratorio, para evitar un diagnóstico y potencial tratamiento inadecuado.

Fibrosis retroperitoneal asociada a neoplasias malignas: Serie de casos clínicos / Retroperitoneal fibrosis associated with malignancies: Report of eight cases

Retroperitoneal fibrosis (RPF) is uncommon. Eight percent of cases are associated with malignancies. The pathogenesis of cancer related RPF (MRPF) is unknown. It may be originated from a desmoplastic reaction of the retroperitoneum to the presence of malignant cells, to the action of cytokines secreted by the tumor or a reactive inflammation. MRPF may also be a consequence of antineoplastic therapy (surgery, radiotherapy and chemotherapy). We report eight cases of MRPF associated with breast, cervix, thyroid, kidney and retroperitoneal cancer. In four patients, retroperitoneal tissue biopsy was performed, showing the typical findings of idiopathic RPF. In 6 patients MRPF appeared one to 15 years after cancer diagnosis and in two, it appeared simultaneously. The clinical presentation, course and therapeutic response are described. Six patients were treated with steroids alone and five with steroids associated with colchicine.

Hiponatremia sintomática como forma de presentación clínica de un macroadenoma hipofisiario: Comunicación de tres casos / Hyponatremia associated to pituitary adenomas: Report of three patients

Severe hyponatremia occurring as the presenting feature of hypopituitarism secondary to pituitary adenomas is rare. We report three patients with this condition: Two elderly males (74 and 78 year-old) presenting with impaired consciousness and low plasma sodium after an episode of diarrhea and a 56-year-old male presenting with impaired consciousness after an episode of vomiting. All had clinical features of hypopituitarism and pituitary adenomas were found on imaging studies. Two were subjected to a trans sphenoidal resection of the adenoma.