Neonatal plasma TSH--estimated upper reference intervals for diagnosis and follow up of congenital hypothyroidism.

Age- and method-dependent plasma TSH reference intervals are essential for the diagnosis and management of congenital hypothyroidism. However, accurate reference intervals for plasma TSH have not been adequately defined due to the difficulties in obtaining samples from a healthy paediatric population. To overcome the difficulties in generating such intervals we estimated method-dependent plasma TSH upper-reference intervals by determining the blood spot TSH upper-reference interval from newborn blood spot TSH screening data (N = 10,697) and then derived method-dependent conversion factors for blood spot TSH to plasma TSH concentration from paired-blood spot and plasma TSH measurements. The upper reference interval for blood spot TSH of 3.04 mU/L was obtained from the 97.5th centile of the selected data. Using experimentally-derived conversion factors, estimates of plasma TSH upper reference intervals of 7.6, 6.3, 7.3, 8.3 and 6.5 mU/L were obtained for the Siemens Centaur, Abbott Architect, Roche Elecsys E170, Siemens Immulite 2000 and Beckman access HYPERsensitive TSH assays respectively. These estimated method-dependent plasma TSH upper reference intervals will be of great practical use to clinicians to diagnose and to follow up infants found to have increased blood spot TSH concentrations identified by Newborn Screening programmes.

A rare cause of Cushing's syndrome demonstrates analytical discrepancies between the Roche E170 and Bayer Centaur testosterone assays.

The initial biochemical investigations of a female patient with suspected Cushing's syndrome revealed abnormal endocrine results, including a marked elevation of serum testosterone. Overnight and low-dose dexamethasone suppression tests confirmed the diagnosis of Cushing's syndrome. Imaging investigations revealed an appearance compatible with adrenocortical carcinoma with metastases in the lungs and liver. This tumour is a rare cause of Cushing's syndrome. Two different automated testosterone immunoassays were used during the investigation of this patient, and analytical discrepancies in the patient's testosterone results were found. The two assays used, as well as potential causes of the difference in results will be discussed.