Objective
To make recommendations for screening Canadian newborn infants for
congenital hypothyroidism. This updates a 1990 Canadian Task Force report.
Burden of Suffering
The incidence of hypothyroidism ranges between 1 in 4,000 to 1 in 3,500
live births and can be as high as 1 in 141 live births among infants with
Down Syndrome. Before screening was available, the age at diagnosis
ranged from 1 week to 5 years or more. The intelligence quotient
of 65% of patients with congenital hypothyroidism was below 85 (borderline
mental retardation), and in 19% it was below 15 (profound mental retardation).
Children whose mothers ingested iodides, propylthiouracil or radioactive
iodide or had circulating antithyroid antibodies are at high risk for congenital
hypothyroidism.
Options
Screening is done with dried blood samples tested at 3 to 6 days using
either thyroid-stimulating hormone (TSH) tests followed by thyroxine (T4)
in borderline cases or T4 testing done first. Treatment includes
restoration and maintenance of normal thyroid levels.
Outcomes
Sensitivity and positive predictive values of the screening tests and
recall rates.
Evidence
MEDLINE was searched for 1989 - 1993 using the keywords congenital
hypothyroidism with screening and prevention and control. Only original
articles were included.
Values
The 13-member Task Force of experts in family medicine, geriatric medicine,
pediatrics, psychiatry and epidemiology used an evidence-based method for
evaluating the effectiveness of preventive health care interventions. Recommendations
were not based on cost-effectiveness of options. Patient preferences were
not discussed.
Background papers providing critical appraisal of the evidence and tentative recommendations prepared by the chapter author were pre-circulated to the members. Evidence for this topic was presented and deliberated upon in 1- to 2-day meetings, 2 to 3 times per year from January 1993 to June 1993. Consensus was reached on final recommendations.
Benefits, Harms, and Costs
Dried blood collected on filter paper 3 to 6 days after birth and tested
for TSH with confirmation of either normal or borderline results using
T4 testing has a sensitivity of 95%. Initial testing with T4 has a recall
rate of 1.1% and a positive predictive value of 2.4%.
65% of infants with untreated congenital hypothyroidism have an IQ of < 85 (borderline functioning or lower) and in 19% it is below 15. Eight cohort studies showed that affected infants who were identified and treated had mean IQs >100 and did not differ from control infants. Treated infants did not differ from controls on developmental scales. One of the studies showed that IQ was within normal values for treated infants but marginally lower than for infants in the control group (105 vs 110); these results continued to up to 12 years follow-up.
Screening and early treatment dramatically decrease the morbidity associated with congenital hypothyroidism. The fact that most hypothyroid infants identified at birth by screening have intellectual and psychomotor development in the normal range constitutes a dramatic improvement over the outcomes in children previously diagnosed later in life.
Recommendations
Recommendation grade [A, B, C, D, E] and level of evidence
[I, II-1, II-2, II-3, III] are indicated after each recommendation. Citations
in support of individual recommendations are identified in the guideline
text.
Sponsors
The Canadian Task Force on Preventive Health
Care developed this guideline with funding from Health Canada.
Selected References
Source Document
Beaulieu M.D. Screening for congenital hypothyroidism. In: Canadian
Task Force on the Periodic Health Examination. Canadian
Guide to Clinical Preventive Health Care. Ottawa: Health Canada,
1994;190-4.
Other
Canadian Task Force on the Periodic Health Examination: Periodic health
examination, 1990 update: 1 Early detection of hyperthyroidism and hypothyroidism
in adults and screening of newborns for congenital hypothyroidism. Can
Med Assoc J. 1990;142:955-61.