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Effect of phototherapy on thyroid stimulatory hormone and free thyroxine levels
K L Tan1, Y Chirino-Barcelo, T C Aw
1Department of Neonatology, National University Hospital, Singapore.
Insights
Phototherapy for neonatal hyperbilirubinaemia does not affect thyroid function. Neonatal thyroid screening remains valid when using fibre-optic, daylight, or combined phototherapy treatments.
Area of Science:
- Neonatal Medicine
- Endocrinology
Background:
- Neonatal hyperbilirubinaemia is common and often treated with phototherapy.
- Neonatal thyroid screening is crucial for early detection of thyroid dysfunction.
- The potential impact of phototherapy on thyroid function tests requires investigation.
Purpose of the Study:
- To evaluate the effect of different phototherapy methods on thyroid function in infants with hyperbilirubinaemia.
- To determine if phototherapy interferes with the accuracy of neonatal thyroid screening.
Main Methods:
- Infants with non-haemolytic hyperbilirubinaemia were randomized to receive fibre-optic, daylight, or combined phototherapy.
- Bilirubin levels were monitored, and blood samples were collected for thyroid stimulating hormone (TSH) and free thyroxine (fT4) at various time points.
- A control group of unexposed infants was included for comparison.
Main Results:
- All infants remained well during the study.
- Phototherapy effectively reduced bilirubin levels, with the combination therapy showing the most rapid decline.
- Thyroid stimulating hormone (TSH) and free thyroxine (fT4) levels showed similar age-related declines in both phototherapy and control groups.
- No significant interference of phototherapy with thyroid function parameters was observed.
Conclusions:
- Phototherapy, including fibre-optic and conventional daylight methods, does not compromise the validity of neonatal thyroid screening.
- Thyroid function monitoring during phototherapy can be reliably interpreted.
Objective:
To study the effect of phototherapy for neonatal hyperbilirubinaemia on thyroid function as neonatal thyroid screening is sometimes performed during exposure to phototherapy.
Methodology:
Infants with non-haemolytic hyperbilirubinaemia were sequentially allocated to fibre-optic phototherapy, conventional daylight phototherapy, or a combination of both. Bilirubin concentration was monitored 12 hourly by capillary blood sampling; venous blood was sampled for thyroid stimulating hormone (TSH) and free thyroxine (fT4) determinations, at start of exposure, at 24 h, end of exposure and 1 day later. Comparable unexposed infants served as controls.
Results:
All 123 study infants and 25 controls remained well during the study. Bilirubin levels declined during phototherapy, being most rapid in the combination group. The TSH and fT4 values at start of exposure were 3.86 +/- 0.41 mU/L (mean +/- SEM) and 33.20 +/- 1.16 pmol/L, respectively, in the fibre-optic group, 3.62 +/- 0.38 mU/L and 37.22 +/- 1.76 pmol/L in the daylight group, and 4.40 +/- 0.48 mU/L and 29.91 +/- 1.13 pmol/L in the combined group, compared with 5.77 +/- 0.40 mU/L and 34.46 +/- 1.68 pmol/L in the control group. The TSH and fT4 values declined with increasing age in the phototherapy and control groups with end of exposure values of 2.90 +/- 0.28 mU/L and 27.71 +/- 0.71 pmol/L, 2.77 +/- 0.31 mU/L and 33.52 +/- 1.22 pmol/L, and 3.44 +/- 0.30 mU/L and 27.54 +/- 0.88 pmol/L, respectively, compared with 4.21 +/- 0.61 mU/L and 27.19 +/- 2.33 pmol/L (at 72 h) in the control group. The pattern of TSH and fT4 decline in the exposed and control groups was similar, being related to increasing age.
Conclusions:
The validity of neonatal thyroid screening is not affected by fibre-optic or conventional phototherapy or by both combined.