Hypothermic treatment alters the metabolic profile of newborns, mimicking or masking an inherited metabolic disorder: findings from a monocentric study

Every newborn baby is given a tiny prick on their heel to collect a few drops of blood. This sample is placed on a special card and sent to a laboratory, where scientists scan it for signs of rare, inherited metabolic disorders. These are conditions where the body cannot properly break down food or process certain chemicals, and catching them early is vital for a child's health. For babies born with a specific type of brain injury caused by a lack of oxygen during birth, doctors use a different kind of treatment. They cool the baby's body down for a few days to protect the brain from further damage. This process, known as therapeutic hypothermia, is a standard and life-saving procedure. However, a critical question has lingered: does this cooling treatment change the chemical makeup of the baby's blood in a way that confuses the screening test? If the cold alters the levels of the chemicals doctors look for, the test might falsely flag a healthy baby as sick, or worse, miss a baby who actually has a disorder.

A team of researchers in Italy set out to answer this question by looking directly at the blood of newborns who had received this cooling treatment. They compared the blood samples of sixty-six full-term babies who had undergone hypothermia for brain injury against a group of sixty-nine healthy, full-term babies who had not. All the babies were born at full term and weighed at least 2,500 grams. The researchers took blood samples from both groups between 48 and 72 hours after birth, a standard window for newborn screening. They used a highly sensitive machine to measure the levels of 57 different chemicals in the blood, including amino acids, which are the building blocks of proteins, and acylcarnitines, which help the body burn fat for energy.

The results showed that the cooling treatment did indeed change the chemical landscape of the blood. The researchers found that the levels of several key substances were significantly different in the treated babies compared to the healthy ones. Specifically, the amount of glutamate, a chemical that acts as a messenger in the brain, dropped sharply in the babies who were cooled. At the same time, the level of glycine, another brain chemical, rose noticeably. The treatment also caused a decrease in many of the chemicals that help the body process fat, including several short-chain and long-chain acylcarnitines. Conversely, the levels of a group of fats called phosphatidylcholines increased substantially in the treated group. These changes were not minor fluctuations; for some substances, the difference was so large that it stood out clearly against the background of normal variation.

The researchers explained that these shifts make sense when looking at how the brain and body react to injury and cold. When the brain is starved of oxygen, it becomes overexcited and flooded with certain chemicals that can damage cells. Cooling the body helps calm this storm, reducing the need for the brain to use up these chemicals, which explains why glutamate levels fell in the blood. The rise in glycine appears to be part of the body's attempt to protect the brain from this overexcitation. The changes in fat-processing chemicals suggest that the cooling treatment helps the body return to a more efficient way of burning fuel, reversing the chaotic metabolic state caused by the initial lack of oxygen.

The most important takeaway from this study is not just that the levels change, but that these changes could lead to mistakes in diagnosis. If a baby has a mild inherited disorder that causes slightly high levels of a certain chemical, the cooling treatment might push that level even higher, causing the screening test to flag the baby as having a severe disorder when they do not. On the other hand, if a baby has a disorder that causes low levels of a chemical, the treatment might lower those levels even further, potentially hiding the problem entirely. Because the standard screening test is usually done while the baby is still undergoing this cooling treatment, the results could be misleading.

The authors of the study suggest a practical solution to this problem. They recommend that for any baby who has undergone therapeutic hypothermia, a second blood sample should be taken after the treatment is finished. This would allow doctors to see the baby's true metabolic profile once their body has returned to normal temperature. While the study was limited to a single hospital and a specific group of babies, the findings are clear enough to warrant this extra step. By waiting to take the final sample, screening programs can avoid false alarms and ensure that no baby with a real metabolic disorder is missed, providing a clearer picture of their health as they begin their lives.