You may have seen photos of tiny babies under blue lights, wearing nothing more than a diaper and adorable plastic goggles. Why are they in what looks like a baby tanning booth, instead of comfortably swaddled in their mothers’ arms? Since babies and tanning booths definitely don’t belong together, what’s going on? Those babies are getting the blue-light medical treatment, and the reason for their blues is bilirubin.
Bilirubin is a yellow pigment that’s made when red blood cells die and the iron-binding heme structure in their juicy innards is digested into smaller pieces. Red blood cells only live for 120 days, so it’s completely normal to have a baseline level of bilirubin in your serum; normally, liver enzymes convert free bilirubin into other forms and send it along through the bile duct to the intestines, where it finds its way out of the body for good. While a baby is still in utero, the placenta takes care of filtering out excess bilirubin, which Mom’s body then treats as her own (thanks for doing all that excreting for me, Mom). But when the baby’s born, it’s time for baby’s liver to take over the hard work – and sometimes it can’t quite handle it. It’s a small liver, after all, and those enzymes take some time to reach full capacity.
Neonatal hyperbilirubinemia (aka high serum bilirubin in newborns) is incredibly common – up to 60% of full-term newborns have elevated bilirubin levels in the first few days of their lives. Something as common as bruises from being squeezed through the birth canal can cause bilirubin to be made faster than it can be processed by the baby’s liver. More serious cases arise from mismatches between Mom and baby’s blood types. When the baby’s blood cells carry proteins unfamiliar to the mother’s immune system, her white cells produce antibodies in self-defense. Those antibodies can cross the placental membrane and attack the baby’s red cells, destroying them and leaving excessive amounts of bilirubin behind in the baby’s blood.
If postnatal blood work shows high bilirubin, the medical team usually just follows up with another test in a day or two. If the numbers don’t go down, that’s a very big problem, because bilirubin is toxic.
What are you, yellow?
We call hyperbilirubinemia ‘jaundice’, because when bilirubin builds up in the skin it makes a person look yellow. It’s especially apparent in the whites of the eyes: since they start out with so little natural pigment of their own, they yellow quickly. But the serious damage happens inside the body. If serum levels remain high, bilirubin can build up in the grey matter of the brain and lead to seizures or even permanent motor and intellectual impairment.
That’s where the blue lights come in. This treatment is called phototherapy and it’s been around since the 1950s. Light can break down bilirubin into products that can be excreted from the body without the liver’s help, so putting babies under bright lamps can save their lives by speeding up the removal of bilirubin from their blood. Blue light (in the 420-470 nm range of wavelengths) works best to break up the bilirubin molecule, so that’s what we use in neonatal intensive care units – end result being nearly-naked babies with eyes goggled for safety, chilling out under blue lights for hours while they fill their diapers with bilirubin by-products. Nice!
Phototherapy’s effectiveness depends on light intensity, and on how much skin surface area can be exposed to it. Unfortunately, these blue light setups are expensive. Some crowded hospitals in poorer countries are forced to put two or three babies under one light, and none of them really get an effective dose that way. All kinds of strategies have been proposed to help resolve the overcrowding problem under scarce blue lights, but they all come with a price tag, and many of the places that need this help most desperately just don’t have the budget. There is an interesting TED talk discussing this issue available to view here.
Here comes the Sun
Wait, you say, there’s an easy solution! Put ‘em in the sunlight – that’s free! Well, the Sun’s light isn’t just blue. There’s blue light in there somewhere, but it’s all mixed in with a whole rainbow of colours, plus sunburn-and-cancer-causing ultraviolet light. We don’t exactly want to crisp the babies up like strips of bacon by leaving them out in the sun all day.
A new study conducted in Nigeria and published in The New England Journal of Medicine looked at whether bringing babies out into the sunlight and protecting them under special light-filtering canopies could do as well as traditional blue lights. The plastic canopies used in the study were designed to block UV (to stop the babies from developing sunburn), but allow blue wavelengths to pass through easily. The study deliberately excluded babies with extremely high bilirubin levels, just in case the treatment wasn’t as effective as they hypothesised.
So 447 otherwise-healthy full-term babies with high serum bilirubin were recruited to the study: half were treated with five hours a day of the usual blue light therapy while the other half were sent outside for the same amount of time, to enjoy some sunshine filtered through the special canopies. They were monitored closely for signs of dehydration and hyperthermia, but luckily none of the babies needed to be pulled from the study because they couldn’t take the heat.
Not only did the sunshine treatment appear to be as effective as traditional therapy for these infants, but the babies were able to spend some of their treatment time in their mothers’ arms instead of in a plastic incubator. While they’re too little to fill out patient satisfaction surveys, we have to assume that that cohort of the study enjoyed their treatment a lot more than their blue light buddies.
The study’s authors note that this is probably most practical in a tropical location when the weather is sunny and warm. It would cost more to build protective, climate-controlled “sun rooms” to make the treatment feasible in January in Tibet, or on rainy days in Uruguay. But the sun still shines in winter, and enough light filters through even on rainy days that it would definitely be helpful as an alternative or supplemental treatment for neonatal hyperbilirubinemia.
Let a little sunshine in, and those little yellow babies won’t need to deal with the blues anymore.
Jen MacCormack is a self-described “mad laboratorian” currently working on transforming human plasma into blood typing antisera. She’s approximately 40% coffee by volume and expends excess energy on her growing portfolio of science writing.