Point-of-care testing (POCT) for bilirubin is a rapid diagnostic method performed outside of a central laboratory, typically near the patient’s bedside. This approach is primarily used in newborn screening to quickly detect elevated levels of bilirubin, the compound responsible for the yellowish skin discoloration known as jaundice. POCT devices provide immediate results, allowing healthcare providers to determine if an infant requires further monitoring or prompt intervention in settings like a hospital nursery or outpatient clinic.
Understanding Bilirubin and Jaundice
Bilirubin is a yellowish compound produced as a byproduct of the breakdown of old red blood cells. The process begins when hemoglobin is metabolized into biliverdin, which is then converted into unconjugated bilirubin. This unconjugated form is lipid-soluble and must bind to a protein, typically albumin, to travel through the bloodstream to the liver.
Once in the liver, the bilirubin is chemically processed, or conjugated, to make it water-soluble so it can be excreted in bile and removed from the body. Newborns often experience an accumulation of this unconjugated bilirubin because their red blood cell turnover is high and their liver enzyme, Uridine Diphosphate Glucuronosyl Transferase (UDPGT), is not yet fully functional. This temporary inability to effectively process the compound leads to neonatal hyperbilirubinemia, the underlying cause of visible jaundice.
While most neonatal jaundice is temporary and harmless, excessively high levels of unconjugated bilirubin pose a serious risk because the unbound form can cross the blood-brain barrier. The accumulation of this neurotoxic substance in the brain can cause a type of permanent neurological damage known as kernicterus. The potential for this severe outcome highlights the necessity for timely and accurate screening in every newborn.
The Point-of-Care Testing Approach
Point-of-Care Testing represents a logistical shift in diagnostic medicine, moving the analysis from a centralized laboratory to the patient’s immediate location. This approach dramatically shortens the time required to get a result, which is referred to as the turnaround time. For newborns, this immediate feedback is highly beneficial, as it allows for swift clinical decision-making regarding treatment.
The speed of POCT is especially important for managing neonatal jaundice, since bilirubin levels can rise quickly in the first days of life. Using a portable device at the bedside eliminates the delays associated with sample transport, lab processing, and reporting. This efficiency helps prevent the escalation of hyperbilirubinemia to levels that would require more aggressive intervention. POCT also minimizes the amount of blood required for testing, which is a significant advantage in tiny patients where repeated blood draws can lead to iatrogenic anemia.
Methods of POCT Bilirubin Measurement
POCT utilizes two main methods to measure bilirubin levels in newborns: a non-invasive screening technique and a minimally invasive blood test.
Transcutaneous Bilirubinometry (TcB)
The first method, Transcutaneous Bilirubinometry (TcB), involves placing a handheld device against the infant’s skin, often on the forehead or sternum. This device works using optical spectroscopy, directing light into the skin and measuring the intensity of the light that reflects back. The TcB meter calculates the amount of bilirubin by analyzing the light absorption, which correlates to the yellow pigment in the skin and subcutaneous tissue. TcB is an excellent screening tool because it provides an instantaneous reading without causing discomfort to the baby. It is important to understand that TcB measures bilirubin in the skin, which is related to but physiologically distinct from the concentration in the bloodstream.
Capillary Bilirubin Test
The second method is a capillary bilirubin test, which is performed if the TcB reading is high or near an intervention threshold. This test requires a small blood sample, usually obtained via a heel stick, which is then analyzed by a specialized POCT analyzer. These compact devices often use a dual-wavelength spectrophotometry method, or a chemical reaction like the diazo method, to directly quantify the total bilirubin concentration in the blood. While slightly more invasive than TcB, this blood test is generally considered more accurate for confirming significant hyperbilirubinemia, especially when levels are high, and requires only a minimal volume of blood.
What POCT Results Indicate
The results from POCT bilirubin measurements are not interpreted as static numbers but are assessed in the context of the baby’s exact age in hours. Healthcare providers use specific graphs called nomograms to plot the bilirubin level against the infant’s postnatal age. These nomograms define risk zones and intervention thresholds, which change minute by minute during the first days of life.
If the POCT result falls into a low-risk zone, the baby is typically monitored with repeat testing usually scheduled before discharge or in a follow-up appointment. A reading in a higher-risk zone, or one that is within a few milligrams per deciliter of the phototherapy threshold, immediately prompts a confirmatory blood test, known as a total serum bilirubin (TSB) measurement. The TSB is the gold standard for clinical decision-making and is used to determine the exact need for treatment.
When the bilirubin level crosses the established threshold on the nomogram, the most common next step is to initiate phototherapy, which involves exposing the baby to special blue light. This light changes the structure of the bilirubin molecules, making them water-soluble and easier for the body to excrete without liver conjugation. POCT results, therefore, serve as a rapid screening and triage tool that guides this immediate decision-making process, ensuring timely therapeutic action to prevent potential neurotoxicity.