In the paper by Verma, et al. [1], the words ‘capillary TSH’ and ‘DBS (dried blood spot)’ clarified the source of blood (heel prick) and the assay method, but not the reporting units of thyroid stimulating hormone (TSH), i.e., whole blood units (WBU) or serum units (SU). As the DBS assay output can be set to report TSH in WBU, or else the output can be multiplied by a factor of 2.2 (to adjust for hematocrit) to report in SU, the interpretation of a cut-off of 20 mU/L is not self-evident. In many earlier articles [2], DBS output for TSH is in WBU. A cut-off of 20 mIU/L TSH reported in WBU would be equivalent to a TSH of 44 mIU/L in SU. In a vast country like India, some newborn screening (NBS) programs may assay TSH from a cord blood sample in a routine laboratory (which would automatically report in SU), whereas some doctors may send postnatal heel prick DBS samples to a centralized NBS laboratory, which may report in WBU. To maintain uniformity in the country, the ISPAE guidelines [3] recommend reporting DBS TSH in SU rather than WBU.

Verma, et al. [1] mentioned ‘capillary TSH’ while quoting from a publication from my center [4], where we reported in SU. From this I conclude that they mean SU while talking about their own ‘capillary’ TSH results. On the other hand, they have also quoted papers, where the authors have clearly used WBU [5] presumably interchangeably with their own reporting units. A clarification from the authors regarding their reporting units is thus clearly needed.

There are also a couple of methodological observations also. While drawing ROC curves for the screening TSH cut-off, the true positives and true negatives of those infants who were below the chosen cut- off of 20 mU/L are not known. Therefore, this method may not be appropriate for justifying the screen cut-off for NBS. Secondly, the results of confirmatory test of infants with screen TSH between 10 and 19.9 mU/L revealed three infants to have congenital hypothyrodism. However, we do not know how many may have been positive if, for example, screen cut-off of TSH was kept between 5 and 10 mU/L. It is not clear therefore as to what result has been used to conclude that newborns with screen TSH between 10 and 19.9 mU/L should have a second screen.

1. Verma P, Kapoor S, Kalaivani M, Vats P, Yadav S, Jain V, et al. An optimal capillary screen cut off of thyroid stimulating hormone for diagnosing congenital hypothy-roidism: Data from a pilot newborn screening program in Delhi. Indian Pediatr. 2019;56:281-6.

2. Léger J, Olivieri A, Donaldson M, Torresani T, Krude H, van Vliet G, et al. European Society for Paediatric Endocrinology Consensus Guidelines on Screening, Diagnosis, and Management of Congenital Hypothy-roidism. J Clin Endocrinol Metab. 2014;99:363-84.

3. Desai MP, Sharma R, Riaz I, Sudhanshu S, Parikh R, Bhatia V. Newborn Screening Guidelines for Congenital Hypothyroidism in India: Recommendations of the Indian Society for Pediatric and Adolescent Endocrinology - Part I: Screening and Confirmation of Diagnosis. Indian J Pediatr. 2018;85:440-7.

4. Gopalakrishnan V, Joshi K, Phadke SR, Dabadghao P, Agarwal M, Das V, et al. Newborn screening for congenital hypothyroidism, galactosemia and biotinidase deficiency in Uttar Pradesh, India. Indian Pediatr. 2014;51:701-5.

5. Olivieri A, Corbetta C, Weber G, Vigone MC, Fazinni C, Medda E, et al. Congenital hypothyroidism due to defects of thyroid development and mild increase of TSH at screening: data from the Italian National Registry of Infants with Congenital Hypothyroidism. J Clin Endocrinol Metab. 2013;98:1403-8.