Cord blood thyroxine and thyroid stimulating hormone screening for congenital hypothyroidism: how useful are they?

AIM

To determine and compare the usefulness of cord blood screening for free thyroxine (FT4) and thyroid stimulating hormone (TSH).

BACKGROUND

There is a vast amount of literature on capillary heel prick screening tests, but relatively little on cord blood testing particularly FT4. For a decade all infants born at Tawam Hospital had cord blood FT4 and at Oasis Hospital cord TSH measured through the hospital-based screening programme. On January 1st 1998, the national screening programme (NSP) for congenital hypothyroidism (CH) in the United Arab Emirates (UAE) started using capillary TSH measurement (Delfia method). Since then newborns in both hospitals have been screened both ways, i.e. cord blood and capillary blood screening.

METHODS

We reviewed retrospectively all infants born from January 1998 until the end of June 2004 with CH who had double screening: cord FT4 or TSH and 4th-5th day TSH screening.

RESULTS

Thirteen infants (one in 1,778) had CH in Tawam Hospital. In six of these the cord blood FT4 was low (<9.1 pm/l) (0.73 ng/dl) and in seven the cord blood FT4 was normal, i.e., over half were missed. Eight infants (one in 1,198) had CH in the Oasis Hospital. Cord blood TSH was high in six of them (>13 IU/l) and two were normal. Cord FT4 detected the most severe cases, but missed most others. Cord TSH detected six out of eight cases, but there was a recall rate of one in 23.

CONCLUSIONS AND RECOMMENDATIONS

Cord FT4 identifies only infants with severe CH. Cord TSH is more sensitive than cord FT4 screening. Capillary TSH dried blood spot testing on the 3rd-5th day is the most sensitive method.

Multiple positive results during a neonatal screening program: a retrospective analysis of incidence, clinical implications and outcomes

AIMS

Neonatal screening programs perform different screening tests on the same blood-spot sample collected on a Guthrie card. We retrospectively investigated the incidence of multiple positive results as well as the outcomes and the physical characteristics of newborns with more than one positive result for phenylketonuria (PKU), congenital hypothyroidism (CH) and congenital adrenal hyperplasia (CAH).

METHODS

Neonatal screening was performed on blood-spot for PKU (phenylalanine concentration by fluorescent ninhydrine method), for CH (simultaneous total thyroxin (tT4) and thyroid-stimulating hormone (TSH) levels by fluoroimmunometric assay); and for CAH (17-hydroxyprogesteron level by fluoroimmunometric assay).

RESULTS

During three years of screening, 39 newborns (37 preterms) showed multiple positive results at screening tests (incidence 1:6387). The most frequent positive results were the combinations of CH and CAH (25/39) and PKU and CH (12/39). At recall, only two newborns were confirmed positive and each for only one disease: one, premature baby, for PKU from the PKU and CH combination; the other, born at term, for CAH from the CH and CAH combination.

CONCLUSIONS

Multiple positive results are a rare observation at neonatal screening for PKU, CH and CAH, more frequently observed in preterm babies. However, multiple positive results must not be overlooked because of true positive results at recall.