Factors affecting the serum free thyroxine levels in hospitalized chronic geriatric patients

Unexpected Elevated Free Thyroid Hormones in Pregnancy

BACKGROUND

The use of thyrotropin and free thyroid hormone assays to evaluate thyroid function is widespread, but in some situations the results are inconsistent with the patient's thyroid status.

SUMMARY

A 35-year-old woman with a known diagnosis of chronic autoimmune thyroiditis was referred to the authors' clinic at week 26 of her second pregnancy. The patient was clinically euthyroid. Consistent with this, her serum thyrotropin (TSH) was normal (0.79 mIU/L), but she had elevated free thyroid hormones-free triiodothyronine (fT3) and free thyroxine (fT4)-as determined by a one-step chemiluminescent assay. The patient was taking levothyroxine replacement therapy (125 μg/day), and the dose was confirmed. Previous blood tests showed concordance between TSH and free thyroid hormone values. The patient was followed up throughout gestation and at 12 months postpartum. During gestation, her free thyroid hormones remained high using one-step methods, while the total thyroid hormone concentration values were within the reference range, in agreement with the TSH values. Postpartum fT4 and fT3 values returned progressively to normality, in agreement with the TSH values. The presence of circulating thyroid hormone autoantibodies (THAb) was hypothesized, which are known to interfere, although to a variable extent, with thyroid hormone one-step assays. Using stored frozen sera, this hypothesis was confirmed indirectly by measuring normal levels of fT3 and fT4 with a two-step method, and directly by demonstrating THAb against the two hormones.

CONCLUSION

Despite their relative rarity, circulating THAb may be suspected when laboratory data are not consistent and contrast with the clinical picture. To the authors' knowledge, no previous case of transient appearance of THAb in pregnancy has been described.

Nutritional status and energy expenditure in elderly patients with recent hip fracture during a 2-month follow-up

A 2-month follow-up of nutritional status was performed in forty elderly patients with recent hip fracture. Patients were nutritionally assessed on admission to our rehabilitation unit (day 0), then monthly (day 30, day 60) by measurement of resting energy expenditure (REE), anthropometric, impedance and biological variables. Patients were defined as undernourished (n 13) or normally nourished (n 27) on the basis of mid-arm circumference (MAC) and triceps skinfold thickness (TST) measurements. Seven patients recovered a walking autonomy and were discharged from the hospital before day 30 (group I) whereas thirteen patients were discharged after day 30 (group II); twenty patients remained in the study at day 60 (group III). MAC and TST decreased in normally nourished patients from group III throughout the study whereas they did not change in group II or in undernourished patients from group III. REE values in relation to fat-free mass were increased compared with normal values and were similar in the three groups on day 0; they did not change during the study. Daily energy intake in relation to body weight was higher in group I and increased in group II and in undernourished patients from group III throughout the study. In contrast, it was below the recommended value at day 0 and it did not significantly improve in normally nourished patients from group III. Serum albumin, transthyretin and transferrin levels on day 0 were below reference intervals in the three groups. Albumin levels increased in group III throughout the study. Inflammatory proteins decreased in groups II and III, with C-reactive protein levels returning to normal values in group II by day 30 and in group III at day 60, while orosomucoid levels did not become completely normal over this period. Our findings indicate no improvement in nutritional status in undernourished patients after surgery for recent hip fracture, despite an adequate energy intake. An insufficient spontaneous energy intake for normally nourished patients was associated with a delayed favourable outcome resulting in a prolonged duration of hospitalization. A hypermetabolic state persisted during the 3 months after surgery.

Estudo da Função Tiroideana em Uma População com Mais de 50 Anos

Com objetivo de analisar a freqüência de disfunção tiroideana e de identificar possíveis alterações hormonais decorrentes do envelhecimento, estudamos 198 indivíduos com idade variando de 50 a 85 anos e 106 filhos com idade entre 11 e 49 anos. A prevalência de disfunção tiroideana foi semelhante em ambos grupos (12,6% no grupo de estudo e 14,1% entre os filhos). A presença de um ou dois anticorpos antitiroideanos positivos foi também semelhante entre os grupos (9,1% e 12,3% para os idosos e filhos respectivamente), embora sem correlação disfunção tiroideana. nos idosos. Os níveis séricos de T3 e FT4 foram significantemente menores entre os indivíduos mais velhos quando comparados com os filhos (1,27±0,27 x 1,39±0,31 ng/ml e 0,97±0,29 x 1,18±0,76 ng/dl, respectivamente). Não houve diferença entre os grupos quanto aos níveis de TSH, T4 total e TBG. Concluímos que a prevalência de disfunção tiroideana não foi diferente entre os grupos e que a presença de anticorpos antitiroideanos esteve associada com disfunção da tiróide apenas nos indivíduos mais jovens. A correlação inversa dos níveis de T3 e FT4 com a idade pode refletir uma adaptação à menor necessidade dos hormônios com o envelhecimento.

Thyroxine, thyrotropin, and age in a euthyroid hospital patient population

The diagnosis of thyroid disease now often can be achieved reliably by measuring thyrotropin (TSH) alone. Thyroxine (T4), triiodothyronine, and other analytes are only needed if TSH and the accompanying clinical condition are discordant. We describe here work that confirms the age independence of TSH in both inpatient and outpatient euthyroid hospital populations between ages 20 and at least 80 years, and demonstrates that although free T4 does vary with age, the range of variation remains within the T4reference interval. On this basis, TSH-based thyroid diagnostic algorithms can be used reliably in adults without reference to age-related reference intervals.

Inhibition of serum protein binding of thyroxine in a hypothyroid patient with familial dysalbuminemic hyperthyroxinemia

OBJECTIVE

To investigate unusual free thyroxine (FT4) responses to T4 replacement doses in a hypothyroid patient with familial dysalbuminemic hyperthyroxinemia (FDH).

METHODS

In this FDH hypothyroid patient, serum FT4 concentration by equilibrium dialysis and T4, triiodothyronine (T3), and thyroid stimulating hormone (TSH) determinations were supplemented by thyroxine binding globulin (TBG) and thyroxine binding prealbumin (TBPA) measurements.

RESULTS

Initial thyroid function tests were compatible with hypothyroidism and FDH (T4 = 78 nmol/L, T3 = 1.08 nmol/L, FT4 = 11.6 pmol/L, TSH = 45 mU/L). When she was initially treated with T4 (0.112-0.088 mg/day) there was an increase in FT4 concentration to hyperthyroid levels accompanied by TSH inhibition (FT4 = 31-51 pmol/L, TSH = <0.03 mU/L); the patient also complained of intolerance and nervousness, and T4 treatment was discontinued. Concentrations of thyroxine binding globulin (TBG) and thyroxine binding prealbumin (TBPA) were normal. When T4 therapy was later resumed at a dosage of 0.075 mg/day, there was a marked increase in percent dialyzable T4. The elevation in percent dialyzable T4 during T4 replacement in a patient with FDH is unusual in view of the very large T4 binding capacity of FDH albumin. The presence of an inhibitor that reduced T4 binding by both TBG and FDH albumin probably explains the elevation in percent dialyzable T4 during T4 treatment.

CONCLUSIONS

This FDH patient represents the first case of a putative inhibitor of T4 binding to both TBG and FDH albumin. The inhibition of T4 binding by these disparate proteins suggests that the inhibitor effect is mediated nonspecifically.