A bilimeter is a non-invasive medical device used to screen newborns for high levels of bilirubin, a substance that can cause jaundice. This tool is used by healthcare professionals in settings like maternity wards and newborn intensive care units (NICU) to identify infants who may be at risk for developing severe jaundice. The device gives an immediate reading, allowing for rapid clinical decisions.
Understanding Neonatal Jaundice
Neonatal jaundice is a common condition affecting up to 60% of term and 80% of preterm newborns in their first week. It is characterized by a yellowing of the skin and eyes, which is caused by an accumulation of bilirubin in the blood. Bilirubin is a yellow pigment produced during the normal breakdown of red blood cells.
In newborns, the liver is often not mature enough to process and remove bilirubin from the body efficiently. While this condition often resolves without intervention, monitoring is important. Excessively high levels of bilirubin, a condition known as hyperbilirubinemia, can be harmful to a baby’s developing nervous system.
If left untreated, severe hyperbilirubinemia can lead to a rare type of brain damage called kernicterus. Bilirubin levels in newborns peak two to four days after birth, which may be after they have been discharged from the hospital. Early detection through screening allows for timely management, which involves treatments like phototherapy to help break down the excess bilirubin.
How a Bilimeter Works
A bilimeter functions as a portable spectrophotometer, a device that measures how a substance absorbs light. A healthcare provider briefly places the tip of the device against the baby’s skin, on the forehead or the sternum (chest). The device then emits a harmless flash of light onto the skin’s surface.
The light penetrates the outer layers of the skin, and the device’s sensor measures the light that is reflected back. The yellow bilirubin pigment in the subcutaneous tissue absorbs a certain amount of this light. The bilimeter’s internal algorithms analyze the reflected light to calculate an estimate of the bilirubin concentration in the tissue just beneath the skin.
This entire process takes only a few seconds and is completely painless for the newborn, causing minimal disturbance. The results are displayed on the device’s screen almost instantly, providing immediate information to the medical staff.
Interpreting Bilimeter Readings
The numerical value provided by a bilimeter is a transcutaneous bilirubin (TcB) level. This number is an estimate that serves as a screening result, not a definitive diagnostic value. It is used to identify which infants might require further, more precise testing.
To properly interpret a TcB reading, healthcare professionals plot the value on a specific chart called a nomogram. This chart takes into account the baby’s age in hours, as bilirubin levels naturally rise and fall in the first few days of life. The nomogram helps to classify the baby’s risk of developing severe hyperbilirubinemia as low, intermediate, or high based on their specific age.
A low-risk reading may mean no further action is needed, while a high-risk reading indicates that a confirmatory blood test is necessary. This targeted approach helps to avoid unnecessary procedures for many newborns while ensuring that those at higher risk receive appropriate attention.
Comparing Bilimeter and Blood Tests
The primary method for screening newborns for jaundice is the bilimeter, while the definitive diagnostic tool is a blood test that measures total serum bilirubin (TSB). In contrast to the non-invasive bilimeter, the TSB test requires a blood sample obtained through a heel-prick, which is then sent to a laboratory for analysis.
The main advantage of using a bilimeter is its ability to significantly reduce the number of invasive blood draws performed on newborns. Studies have shown that transcutaneous measurement is a reliable screening method. It is also more accurate than visual inspection alone, which can lead to both under- and over-estimation of jaundice severity.
A blood test is considered the “gold standard” and is required when a bilimeter reading is high or when a baby has certain risk factors. Blood tests are also standard for premature infants or for babies already receiving phototherapy treatment, as the treatment can affect the accuracy of skin readings.