Overall usefulness of newborn screening for congenital hypothyroidism by using free thyroxine measurement

[helvella]

Yet another cogent reason the TSH test is inadequate. Thyroid hormone measurement finds problems that are missed by TSH.

Endocrine Journal

Vol. 61 (2014) No. 10 p. 1025-1030

doi.org/10.1507/endocrj.EJ1...

ORIGINALS

Overall usefulness of newborn screening for congenital hypothyroidism by using free thyroxine measurement

Akiko Soneda1), Masanori Adachi1) 2), Koji Muroya1), Yumi Asakura1), Yuji Yamagami2) 3), Fumiki Hirahara2) 4)

1) Department of Endocrinology and Metabolism, Kanagawa Children’s Medical Center, Yokohama 232-8555, Japan 2) Neonatal Mass-screening Committee, Kanagawa Prefecture Medical Association, Yokohama 231-0037, Japan 3) Kanagawa Health Service Association, Yokohama 236-8530, Japan 4) Department of Obstetrics and Gynecology, Yokohama City University School of Medicine, Yokohama 236-0004, Japan

Released on J-STAGE 20141031 [Advance Publication] Released 20140802

In Kanagawa Prefecture, Japan, simultaneous measurements of free T4 (FT4) and TSH levels are performed during newborn screening for congenital hypothyroidism (CH). FT4 measurement enables the detection of CH of central origin (CH-C), the incidence of which is estimated to be 1 in 30,833 live births in Kanagawa Prefecture. In this study, we aimed to evaluate the efficacy of FT4 screening when transient CH-C and thyroidal CH (CH-T) with delayed TSH elevation are included as screening targets. Data collected on CH-C patients using a regional survey, as well as data from a database created by a screening organization, were used. Of the 24 CH-C patients who had been born in Kanagawa Prefecture between 1999 and 2008, a positive screening result for FT4 (<0.7 ng/dL) was obtained in 13 newborns; of these, 12 were identified solely through newborn screening. Of the 113 patients for whom positive screening results were obtained during the study period, 5 and 6 were found to have transient CH-C and CH-T with delayed TSH elevation, respectively. Remarkably, 4 out of 5 patients with transient CH-C and all patients with CH-T with delayed TSH elevation were diagnosed through the evaluation of low FT4 at screening. These results indicate that the use of this FT4 screening system facilitates the identification of transient CH-C and CH-T with delayed TSH elevation, thus justifying the inclusion of these entities as screening targets.

Keywords: Congenital hypothyroidism, Free thyroxine, Neonatal screening, Thyroid stimulating hormone, Transient central hypothyroidism

Full paper freely available at link:

jstage.jst.go.jp/article/en...

[Clutter]

Thanks Helvella. I *wish* it could be accepted that TSH is less exquisitely sensitive than most doctors accept.

[helvella Administrator in reply to Clutter]

Clutter,

As I see it, that oft-repeated statement has an odd history.

The idea of TSH rising substantially in response to lowered thyroid hormone levels has been shown repeatedly to have many caveats and is not acceptable as a universal criterion. (We are seeing similar issues arising over the HbA1c test beloved of diabetes medics. There are those who question whether it really is susceptible to the simplistic interpretation so often applied.)

But the wording is often such that the only interpretation possible is that it is the test itself that is exquisitely sensitive. The ability of science to produce three generations of TSH test, each one substantially more sensitive than the previous one, could possibly allow the boast of it "exquisitely sensitive". That is, we see ever decreasing lower-end of measurement.

Trouble is, as soon as TSH is significantly below reference range, we see the panic set in. It really doesn't matter if the TSH can measure down to 0.001, 0.01, or 0.1 - all are treated identically. "Cut your dose!" Or, for the hyperthyroid among us, "Increase your dose of carbimazole".

We have ended up with a TSH test that is exquisitely sensitive in the scientific sense of detecting extraordinarily small amounts of TSH. But a TSH test which is a blunt instrument at the clinical coalface.

[Clutter in reply to helvella]

Helvella, I should, of course, said 'exquisitely sensitive TSH test'. Bad enough that adults can be symptomatic when dose according to it, but it's tragic that the development and IQ of babies may be damaged because their low hormone is missed by TSH only testing.

[helvella Administrator in reply to Clutter]

No criticism intended - they interpret it as if the test and the changes in TSH are both exquisitely sensitive. Completely ignoring the simple fact that in most people the circadian variation is at least enough to make a difference to diagnosis.