FIG. 3.
Phototherapy. (A) For both BB fluorescent (purpled circles) and LED (blue diamonds) systems, irradiance decayed as a function of distance from the source (r2 = 0.98, P < 0.0001). (B) Decay was less marked for LEDs, which emitted 44%-109% higher irradiance within the standard operating range of 30-60 cm from the skin (gray background). (C) The clinical impact of this difference is shown for 2 representative UGT1A1 c.222C>A homozygotes (indicated by green circles and purple diamonds), whose switch from the BB fluorescent (white background) to LED system (gray background) reduced serum bilirubin concentrations. (D) Total bilirubin (BT, left y-axis) and its molar ratio to albumin (BT/A, right y-axis) were lower in patients treated with the LED system. (E) Despite relative uniform phototherapy conditions over time, total bilirubin (BT) and its ratio to albumin (BT/A) increased with age (n = 28; r2 = 0.21, P < 0.0001; purple line with 95% confidence interval). Patients who developed kernicterus (blue diamonds) all had serum BT concentrations that exceeded intravascular binding capacity (BT/A = 1.0 mol:mol; gray horizontal line). (F) Factors underlying this increase are an age-related decrease of “treatable” body surface area relative to plasma volume (an index of the proportional bilirubin load exposed to blue light), increased skin thickness from infancy to adulthood, and progressive hepatopathy. Abbreviation: BSA, body surface area.