Undetectable serum thyroglobulin due to negative interference of heterophile antibodies in relapsing thyroid carcinoma.

come. In both models, the only significant associations observable for men were between GC3 and UFF ( , 3.7; P 0.01) and GC3 and UFF UFE ( , 10.3; P 0.01). In women, in addition to a priori adjusted GC3, nitrogen also showed an association with UFF, resulting in a total explained variation of 47% (Table 1) for UFF alone. However, with UFF UFE as the outcome, total R in women increased to 0.72 and—in addition to urinary nitrogen—plasma leptin also explained a significant portion of variation of potential fGcA after adjustment for glucocorticoid secretion (GC3; Table 1). In line with the known stimulating effect of increased 5a-reductase activity on cortisol clearance, a trend (P 0.057) for a negative association of this enzyme’s activity index (5a-THF/THF) with UFF UFE was seen (Table 1). Accordingly, metabolic and nutritional influences on fGcA (assessed in 24-h urine samples) can be unraveled if the influence of the adrenocortical secretory activity is taken into account (e.g., as GC3). With both UFF UFE and UFF (the conventional measure for fGcA), increases in the protein intake–related postmeal plasma cortisol, as reported in the literature, are mirrored by the significant positive values for 24-h nitrogen excretion rates. However, the frequently reported interaction of leptin with the hypothalamus-pituitary-adrenal axis and the 5a-reductase influence on cortisol clearance remain masked if only UFF is analyzed. A major limitation of our study is that no individuals with abnormal glucocorticoid values were examined. Although recent findings (2, 4) and the present data suggest that UFE may be a useful complementary analyte to UFF for a more meaningful assessment of fGcA, further studies on healthy individuals and hypercortisolemic patients are required before manufacturers can be encouraged to develop adequate multiple glucocorticoid metabolite immunoassays for clinical use. Grant/funding support: None declared. Financial disclosures: None declared.