How Rapid Is “ Rapid ” ?

Once again, lack of judicious editorial constraint on the part of Clinical Chemistry in allowing the inappropriate use of terms such as “more rapid,” “more efficient,” and “more prompt” to describe a new modification of pre-existing methodologies has struck a levance”chord in us (1). In this instance, the article in question describes a simultaneous radioimmunoassay of thyroxine (T4) and thyrotropin (TSH) with ‘ ‘I and 125! as radiolabels, respectively, for mass screening of congenital hypothyroidism in neonates (2). Given all other factors equal, we concur that simultaneous assay of both T4 and TSH is potentially attractive, because both hormones together constitute the most efficient and reliable screen for congenital hypothyroidism. However, we strongly object to the inappropriate use of comparisons such as “rapid,” “enables more prompt therapy,” “more efficient,” “more thorough,” etc., in describing an assay which, for practical and technical reasons, is inferior to readily available existing methodologies. Specifically, the assay described required two 24-h incubations with results available within 72 h of collection. The authors then state that “although T4 and TSH may be assayed separately (by conventional assays) in 8 h, such a short assay is not yet available for simultaneous measurements.” The significance of this statement is a mystery to us as it must be for anyone routinely assaying TSH and T4. Many accurate and reliable commercial T4 assays are now available that can be performed in 1-2 h. Routine assay of TSH is also performed in 3.5-24 h with commercial reagents (Table 1). Therefore, we fail to see the logic of promoting Table 1. Precount incubation Times of Some Commercial TSH RIA Kits