With reference to the recent publication [1] on screening of
hypothyroidism, we wish to submit following observations:
Authors have reported that total number of patients
under study was 1950 while the total as per the table is 1952. In text,
authors state that there were 397 premature and 1551 full term neonates.
This makes the total 1948! It is also remarkable that the male to female
ratio is 0.53:1 (682 males to 1268 females).
Authors state that they could pick up one extra case
with cord blood cut-off of 10 mg/mL but they had false positive rate of
20% in the bargain. Authors report that they repeated thyrotropin
stimulating hormone (TSH) at 72 hours for screen positives, and those
with rising trends were evaluated at day 5 and day 12. With this
protocol a baby with congenital hypothyroidism with raised cord blood
TSH with steady or little less TSH at 72 hours is likely to be missed.
Guidelines by American Academy of Pediatrics [2] do not mention a rising
trend but values above cut-off for repeat sample to be considered screen
positive if first sample is an early sample [2].
With the study methodology, every 5th baby had to be
called for repeat evaluation resulting into higher costs as well as
unnecessary parental anxiety. This could have been easily avoided with
first screen sample after 72 hours followed by recall of screen
positives for confirmation. In case of premature babies, repeat sampling
could have been done later (may be at 2 weeks) in view of delayed
maturation of hypothalamus-pituitary-thyroid axis [2,3]. Authors also
have not mentioned whether the hypothyroid newborn with cord blood
thyroxine of 18 mU/L was preterm or the mother had thyrotoxicosis.
Authors also should have stated whether the two hypothyroid babies
picked up at 2 weeks had prematurity or any accompanying maternal
condition.
The findings of this study once again stress the
importance of sampling after the TSH surge is over and having a proper
cut-off to minimize false positive rate. Sampling at 4 or 5 days
followed by recall of screen positives for confirmatory test will
involve sampling only twice as against 3 or 4 times as in this study. As
cord blood TSH is known to have higher false positive rate, this
strategy may increase the cost and parental anxiety [4,5].
References
1. Anand MR, Ramesh P, Nath D. Congenital
hypothyroidism screening with umbilical cord blood: Retrospective
analysis. Indian Pediatr. 2015;52:435-6.
2. American Academy of Pediatrics, Susan R. Rose SR,
MD, and the Section on Endocrinology and Committee on Genetics, American
Thyroid Association, Brown RS, and the Public Health Committee, Lawson
Wilkins Pediatric Endocrine Society. Update of newborn screening
and therapy for congenital hypothyroidism. Available from:
www.pediatrics.org/cgi/doi/10.1542/peds.2006-0915. Accessed June 14,
2015.
3. Bhatia V. Congenital hypothyroidism is not always
permanent: Caveats to newborn thyroid screen interpretation. Indian
Pediatr. 2010;47:753-4.
4. Gupta A, Srivastava S, Bhatnagar A. Cord blood
thyroid stimulating hormone level – Interpretation in light of perinatal
factors. Indian Pediatr. 2014;51:32-7.
5. Gambhir PS. Cord blood TSH for screening of hypothyroidism:
Is it justified? Indian Pediatr. 2014;51:503.