[Effect of light on total micro-bilirubin values in vitro]

In order to elucidate the effect of light on total bilirubin values in vitro, 616 capillary blood samples were collected from jaundiced newborn infants at the nursery of Veterans General Hospital-Taipei. Samples were divided into 3 groups: 1. Phototherapy light group-133 samples were irradiated with blue fluorescent light (spectral irradiance 425-475 nm = 4 mu watt/cm2/nm); 2. Room light group-202 samples were irradiated with white fluorescent light (spectral irradiance 425-475 nm = 0.2 mu watt/cm2/nm); 3. Dark group-the last 215 samples were placed in the dark. Total bilirubin values were checked with spectrophotometry, at 0, 2, 4, 6, 24 and 48 hours after being placed in different environments. Total bilirubin values varied significantly in different light source and time groups (p less than 0.0001), plus both had statistical interactions (p less than 0.0001). There were significant decreases in the bilirubin values of the phototherapy group beginning at 2 hours (p less than 0.05), and in the room light group beginning at 6 hours (p less than 0.05), but there was no change in the dark group. We conclude that blood samples for total bilirubin values should not be placed under the light of phototherapy even 2 hours. If blood samples are exposed to room light inevitably, it is safe to be checked within 4 hours. If immediate measurements are unavailable, the samples can be placed in a dark environment allowing the values to remain unchanged for 48 hours.