J. Endocrinol. Invest. 7: 29, 1984

Serum thyroglobulin determinations in the differential diagnosis of congenital hypothyroidism

F. Pacini*, R. Lari*, P. La Ricca***, L. Grasso*, F. Di Bartolo***, G.F. Fenzi*, M. Ciampi*, S.G. Gragnani***, L. Baschieri*, and A. Pinchera** *Cattedra di Patologia Medica 2, **Gattedra di Endocrinologia e Medicina Costituzionale, Universita di Pisa, Via Roma 67, 56100 Pisa, and ***Divisione Pediatrica, Ospedale Civile di Cecina, 57023 Cecina, Italy

ABSTRACT. The value of serum thyroglobulin (Tg) determination in the differential diagnosis of congenital hypothyroidism was assessed by serum Tg measurements in 14 patients with proven congenital hypothyroidism, in 3 subjects with transient perinatal hypothyroidism, in 3 newborns with congenital thyroxine binding globulin (TBG) deficiency and in 34 normal controls. Serum Tg was undetectable in all 6 cases with thyroid agenesis, normal or moderately elevated in the 4 cases with ectopic thyroid, markedly increased in the 4 cases with dyshormonogenic goiter and normal in the 3 caseswith transient hypothyroidism and in the 3 with TBG deficiency. The present data indicate that serum Tg measurements may be useful in the differentiation of athyreotic hypothy­roidism from other conditions of congenital hypothyroidism.

INTRODUCTION Thyroglobulin (T g) is secreted by the thyroid gland and is detectable in the serum of normal adult subjects (1-3). Serum Tg is elevated in patients with hyperstimu­lated thyroids and in patients with metastatic differen­tiated thyroid cancer while it is low or undetectable in those free of recurrent disease after total thyroidec­tomy (4-6). T 9 is always detectable in the cord blood of normal newborns with mean values higher than those in normal adults and in pregnant women at delivery (7 -11). We confirmed these findings in a very large population of newborns and demonstrated that 1'g re­mains detectable during the. first week of life (12). Re­cently a few studies in newborns with congenital hypo­thyroidism have suggested that serum Tg measure­ments may be useful in the diagnosis of this condition (13, 14). In the present study we re port the results of serum Tg measurements in a group of newborns and children with proven congenital hypothyroidism of dif­ferent etiologies, some of whom were detected in our screening program for congenital hypothyroidism and others referred to us from other institutions. In addition, 3 newborns with congenital thyroxine bind­ing globulin (TBG) deficiency and 3 with transient hypo­thyroidism were studied.

MATERIALS AND METHODS Congenital hypothyraid subjects. A total of 14 patients

Key-words: Thyroglobulin, congenital hypothyroidism, TBG

Correspondence. F. Pac,n, MD. Cattedra di Patologia Medica 2. Universita di Pisa. V,a Roma 67. 56100 Pisa.ltaly

Rece,ved July 10. 1983; accepted September 10. 1983

29

with congenital hypothyroidism (6 newborns detected during our screening program and 1 newborn and 7 children diagnosed during the first year of life referred from other institutions) were available for study. In the seven patients diagnosed at birth, thyroxine (T4 ) and thyrotropin (TSH) were measured in dried filter paper spots obtained at 3-4 days of life . Hypothyroidism wa.s confirmed in all patients by measurements of serum concentrations of T 4' TSH, triiodothyronine (T 3) and T3

resine uptake (T 3U), at a later life. ' A thyroid scan was performed in all cases after more than 18 months of age. Serum Tg'was measured in all patients either before institution of thyroid medications and after withdrawal of therapy. In one patient serum cord blood was also available.

Transient hypothyroidism. This condition was present in 3 newborns in whom thyroid hormone levels were in the hypothyroid range at birth, but were in the normal range when they were recalled.

Congenital TBG deficiency. Three infants with congen­ital TBG deficiency were detected during our screen­ing program for congenital hypothyroidism. They were diagnosed on the 'basis of low T4 and normal TSH values with high T3U and low TBG values. Two were males with absent TBG and 1 was a female with low but detectable serum TBG concentration.

Normal contrals. Eight infants (1-3 months of age) and 26 children (5-16 years old) were studied as the normal control population for these age groups.

Serum Tg measurements. Serum Tg was measured by radioimmunoassay as previously described·(2). All se­ra were screened for the presence of anti-T 9 autoan­tibodies and were negative in all subjects.

F. Pacini, R. Lari, P. La Ricca, et al.

Serum T4 , T3 , T3U, TSH, TBG and spotT4 andTSH were all measured using commercial kits (T3 , T4 and T3U kits were from Miles Lab., Cavenago, Milano; TSH kit was from Diagnostic Product Corporation, Los Angeles, Cal­ifornia; TBG kit was from Corning, Medfield, Massa­chussets; spot T 4 and spot TSH kits were from Biodata, Roma).

RESULTS

In 7 patients in whom hypothyroidism was diagnosed during the first week of life Tg was measured in serum sampies collected during the first two months of life. In the 7 patients who were not screened at birth, hypothy-

roidism was detected during the first year of life and Tg measured on serum sampies obtained at the time of referral to our clinic, between the age of 3 and 16 years; they were off thyroid replacement therapy. Results of thyroid function tests, Tg measurements and thyroid scans in patients with congenital hypothyroidism, tran­sient hypothyroidism and congenital TBG deficiency are summarized in Table 1. In 6 patients hypothyroid­ism was due to thyroid agenesis. In 8 patients with undetectable or low T 4 and high TSH values, thyroid scan revealed the presence of an ectopic (sublingual) thyroid in 4, and a diffuse goiter in the other 4. In 3 subjects hypothyroidism was suspected on the basis of low T 4 and high TSH values on blood spot but they were

Table 1 - Tg, thyroid hormones, TSH, TBG and thyroid scan in subjects with congenital hypothyroidism, transient hypothyroidism, congenital TBG deficiency and in normal subjects.

Blood spot 1.2 SERUM

Subject Sex T4 TSH Tg T3U T4 T3 TSH TBG Age ThyrOid scan No !lg/dl !lU/mi ng/ml % !lg/dl ng/dl !lU/mi !lg/ml

Congenltal hypothyroidism

M 7.8 > 200 < 1253 33 < 1.5 < 37.5 > 100 30 days Agenesis

2 4.2 185 < 1.25 27.9 < 1.5 < 37.5 >100 45 days Agenesis

3 <125 312 < 1.5 < 37.5 88 10 years Agenesis

2.8 >200 < 1.25 19A < 1.5 51 >100 22 days Agenesis

1.9 >200 < 1.25 < 1.5 < 37.5 > 100 14 days Agenesis

6 3.5 >200 < 1.25 < 1.5 >100 14 days Agenesis

M 3.0 > 200 200 38.4 4.6 156 > 100 30 days Ectop'c

8 44 28.5 2.9 129 100 12 years Ectop'c

9 M 167 50.1 < 1.5 < 37.5 66 3 years Ectopic

10 M 45.1 2.9 82.0 100 16 years Ectop'c

11 500 33 < 1.5 < 37.5 45 16 years Goitre4

12 1000 3.1 >100 8 years GOitre4

13 1000 4.8 >100 9 years GOitre5

14 M 450 2.5 > 100 7 days Goitre6

Congenltal TBG deflciency

15 M 2.3 < 12.5 82 85.2 28 55.0 3.3 < 0.5 27 days Normal

16 M 2.6 < t2.5 41 52.5 2.0 80.0 2.6 < 0.5 28 days Normal

17 4.8 < 12.5 130 717 6.9 201 < 0.5 125 48 days Normal

Transient hypothyroidlsm

18 M 7.2 > 200 96 24.8 5A 204 23.9 21 days Normal

19 M 3.1 52 120 31.5 < 1.5 154 > 100 30 days Normal

54 300 9.3 247 1.2 3 months

20 7.2 130 106 44A .11.0 319 15 60 days Normal

Normal controls

(8)7 68± 11 8 38± 1.8 8A ± 0.6 211 ± 16 2.4 ± OA 1-3 months

(26)7 15± 22 30 ± 0.9 7.0 ± 0.3 203 ± 6.6 2.6 ± 02 5-16 years

1 Blood spot determinations were carried out in day 3-4 of life; they are available only in newborns detected in our screening program

2Normal spot T4 and spot TSH values in our laboratory are> 7.2119/dl and < 5011U/ml, respectively. 31n this patient Tg was also undetectable in the cord blood serum.

4Perchlorate dlscarge test positive. 5Dehalogenase defect.

6Not yet studled 7Number in parenthesis represents the number of subjects studied. 8M± SE

30

1000

100

E "­Cl c (9 f-

10

1.25 nd

Agenesis n:=6

-

-

---••••• 0

HYPOTHYROID Sub- With

lingual gOltre n=4 n=4

00

0

•

• 0

0

0

1--- 1---

Transient Hypo-TBG Normals

n=3 n=3 n = 34

• • • • • • • • • -. • 0 • ·0

000

00

D~: o 0

0 0

0 000

---- -- ---00

Fig.1 - Serum Tg levels in subjeets with eongenital hypothy­roidism due to different etiologies, in patients with eongenital TBG delieieney and in normal subjeets. Closed eireles indi­eate subjeets between 1 and 3 months 01 age, open eireles indieate ehildren 01 more than 3 years 01 age. In the normal group, solid bar represents the mean lor elosed eire/es, open bar is the mean lor open eireles. The broken horizontalline is the limit 01 deteetability 01 our assay. Tg eoneentrations are in log seale. nd = not deteetable.

Serum thyroglobulin in congenital hypothyroidism

considered to have transient hypothyroidism since their hormone levels were in the normal range when tested again 20 to 45 days after birth. In 3 additional subjects, spot T 4 value was low and spot TSH undetect­able. T 3U and TBG measurements in the sera of these newborns revealed congenital TBG deficiency. As shown in Figure 1, serum Tg values were undetec­table « 1.25 ng/ml) in the 6 patients with thyroid agenesis, normal or mOderately high in those with ec­topicthyroid (m ± SE = 1 04 ± 46 ng/ml) and extremely high in those with dyshormonogenic goiter (737 ± 151 ng/ml). In patients with transient hypothyroidism or TBG deficiency, serum Tg values were always detec­table with mean values of 107 ± 6.9 and 69 ± 9.6 ng/ml, respectively. Serum Tg values in normal sub­jects between 1 and 3 months of age were 68 ± 11 ng/ ml and in normal subjects between 5 and 16 years of life were 15 ± 2.2 ng/ ml. The effects of thyroid replacement therapy on serum T 9 values are shown in Table 2. As expected in patients with undetectable serum Tg values while off thyroid therapy, no change was observed after institution of thyroid medications. Serum Tg values in patients with thyroid tissue decreased significantly' from pretreat­ment values when on thyroid replacement therapy. A decrease in serum TSH was also observed.

DISCUSSION Congenital hypothyroidism is a disease affecting about 1 in 3,000-4,000 newborns (15). Currently, most screening programs for detecting this condition are based on T 4 and TSH measurements on dried filter paper blood spots during the first week of life and, if hypothyroidism is suspected, on serum T4 and TSH values. With this procedure the differential diagnosis between the various forms of congenital hypothyroid­ism is usually not possible and is delayed until a thyroid scan can be carried out, usually at about 2 years of life,

Table 2 - Serum Tg and TSH belore and alter institution 01 replaeement therapy with I-thyroxine in hypothyroid subjeets.

Patients diagnosis Belore therapy U nder therapy No Tg' TSH2 Tg TSH

Thyroid agenesis < 1.25 > 100 < 1.25 <0.6

2 Thyroid agenesis < 1.25 > 100 < 1.25 3.9

3 Thyroid agenesis < 1.25 88 < 1.25 <0.6

4 Thyroid agenesis < 1.25 > 100 < 1.25 <0.6

8 Eetopie thyroid 44 > 100 25 <0.6

7 Eetopie thyroid 200 > 100 40 <0.6

1 Tg is In ng/ml; 2TSH is in JlU I ml

31

F. Pacmi, R. Lari, P. La Rlcca, el al.

after temporary withdrawal of thyroid hormone re­placement therapy. Our data in subjects with congenital hypothyroidism of different etiologies, suggest that serum T 9 determina­tions are useful in the differential diagnosis of congeni­tal hypothyroidism before a thyroid scan is performed. In agreement with previous observations (13, 14, 16) in newborns with congenital hypothyroidism, serum Tg was undetectable in all our subjects with thyroid agenesis. In one of these patients, Tg was also unde­tectable in the cord blood. Unfortunately, cord blood was not available in the other patients. In contrast, normal or elevated serum Tg values were observed when hypothyroidism was due to ectopic thyroid or to a dyshormonogenic goiter. The small number of cases in these groups do not permit a cut-off point which could differentiate between these two con­ditions, although serum T 9 values in the goitrous pa­tients were significantly higher than in those with ectop­ic thyroid. Two other studies (17, 18) reported detectable serum Tg in patients with ectopic thyroid and undetectable in athyreotic sUbjects, findings which are in agreement with the present data. However, in 3 out of 10 hypothy­roid patients with thyroid gland in a normal position on scanning, Black et al. (17) found no detectable serum Tg. Similarly, one of the 3 goitrous patients studied by Czernichow et al. (18) had undetectable plasma Tg values. These findings were taken as evidence of a structural abnormality of T 9 or failure of its synthesis. We did not observe similar patients in our series, but agree that this possibility should be ruled out in the absence of detectable circulating.T g. To our knowledge data on serum Tg in newborns with congenital TBG deficiency have been not previously reported. The present study indicates that the finding of normal serum Tg in association with low serum T4 and normal serum TSH provides some additional support to the suspicion of congenital TBG deficiency, a condition which is encountered in screening programs with a frequency of about 1 in 8,000-9,000 newborns (19, 20). Finally, serum T 9 determination cannot differentiate patients with transient hypothyrodism from those with permanent congenital hypothyroidism with functioning thyroid tissue.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the cooperation of Or. Marla Carta SorClni and Or. Vincenzo Macchia. who provided so me of the serum sampies fram hypothyroid subjects, and Or. LE Braverman for helpful suggestion in the preparatlon of the manuscript.

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Serum thyroglobulin in congenital hypothyroidism

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