Abstract
Stinca et al. (1) present in vitro validation data from which they recommend the use of a “field-friendly” dried blood-spot (DBS) thyroglobulin assay to monitor iodine nutrition. Unfortunately, this study did not investigate the effects of pre-analytic variables, specifically hematocrit and ambient temperature and humidity, on DBS thyroglobulin measurement. Hematocrit alters the rheological properties of blood dried onto filter paper, affects the distribution of serum proteins in DBS, and introduces error into the quantitative recovery of analytes from DBS (2,3). Temperature and humidity excursions to which DBS are exposed during shipment alter the integrity of many proteins, including thyrotropin and trypsinogen (4).
Serum thyroglobulin measurement can be a useful index of iodine intake and a laboratory aid in the diagnosis of athyreosis (5). The DBS thyroglobulin immunoassay may be convenient and inexpensive. It also may be inaccurate and unreliable. Demonstrating that the method is “field-friendly” requires field studies to evaluate the effects of pre-analytic factors, specifically hematocrit and ambient temperature and humidity, on DBS thyroglobulin immunopotency and quantification. U.S. Food and Drug Administration medical device guidelines recommend that three studies, each of which has an n > 60, be performed at three individual sites by personnel who are the intended users of the device. Stinca et al. (1) have validated DBS thyroglobulin measurement in a laboratory environment. For field use, an additional series of studies should be performed in the field by the intended users. These studies should address the range of hematocrit values encountered in newborns, as well as the effects of ambient temperature and humidity to which dried blood spots will be exposed prior to laboratory analysis.