What is the role of phototherapy in the treatment of hemolytic disease of the newborn (HDN)?

Updated: Dec 28, 2017
  • Author: Sameer Wagle, MBBS, MD; Chief Editor: Muhammad Aslam, MD  more...
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Answer

Despite of the first use of phototherapy by Cremer and associates more than 40 years ago, no standard method for delivering phototherapy is yet available.

  • Phototherapy units differ widely with respect to the type and size of lamps used. The efficacy of phototherapy depends on the spectrum of light delivered, the blue-green region (425-490 nm) of visible light being the most effective; irradiance (µW/cm2/nm); and surface area of the infant exposed.

  • High-intensity phototherapy first described by Tan in 1977 uses irradiance greater than 25 µW/cm2/nm up to 40 µW/cm2/nm when a dose-response relationship to bilirubin degradation reaches a plateau.

  • Nonpolar bilirubin is converted into 2 types of water-soluble photoisomers as a result of phototherapy. The initial and most rapidly formed configurational isomer 4z, 15e bilirubin accounts for 20% of total serum bilirubin level in newborns undergoing phototherapy and is produced maximally at conventional levels of irradiance (6-9 µW/cm2/nm).

  • The structural isomer lumirubin is slowly formed, and its formation is irreversible and is directly proportional to the irradiance and surface area of skin exposed to phototherapy. Lumirubin is the predominant isomer formed during high-intensity phototherapy. [43]  Decrease in bilirubin is mainly the result of excretion of these photoproducts in bile and removal via stool. In the absence of conjugation, these photoisomers can be reabsorbed by way of the enterohepatic circulation and diminish the effectiveness of phototherapy.


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