Bilirubin is a yellowish byproduct formed during the normal breakdown of red blood cells. When this substance accumulates in the bloodstream beyond normal limits, the condition is known as hyperbilirubinemia, causing the yellow discoloration of the skin and eyes referred to as jaundice. Point-of-Care Testing (POCT) is a diagnostic strategy that moves laboratory analysis closer to the patient, facilitating rapid results outside of a central hospital lab. POCT bilirubinometry involves using small, portable devices to quickly measure bilirubin levels, providing immediate data to healthcare providers for timely medical decisions.
Principles of Measurement
Point-of-care bilirubinometry employs two distinct technical approaches. The most common method, Transcutaneous Bilirubinometry (TcB), is non-invasive, using advanced optical technology to estimate bilirubin concentration in the skin. This handheld device works on the principle of reflectance spectrophotometry, directing light into the skin, typically on the forehead or sternum. Bilirubin absorbs light most strongly in the blue-green spectrum, specifically around 460 nanometers.
The TcB device measures the intensity of light reflected back from the subcutaneous tissues, correcting for other light-absorbing substances like melanin and hemoglobin. By analyzing the reflected light intensity across multiple wavelengths, the device calculates a transcutaneous bilirubin value that correlates with the concentration in the blood. This provides an instantaneous, estimated reading without requiring a blood sample.
The second type of POCT device uses handheld photometers to analyze micro-samples of blood, similar to a glucometer. This approach requires a small blood sample, usually obtained from a capillary stick, which is applied to a disposable testing strip or cartridge. The device uses photometric techniques to measure light absorption directly within the sample. Since hemoglobin interferes with bilirubin measurement, the device separates the plasma from red blood cells before determining the total bilirubin concentration.
Primary Clinical Application
The primary clinical application of POCT bilirubinometry is the screening and monitoring of Neonatal Jaundice. Jaundice is common, affecting 60% of full-term and 80% of premature infants in the first week of life due to immature liver function. The rapid accumulation of unconjugated bilirubin poses a risk because high concentrations can cross the blood-brain barrier. If untreated, this can lead to permanent neurological damage known as chronic bilirubin encephalopathy, or kernicterus.
The non-invasiveness of POCT is highly beneficial in the immediate postpartum period. Healthcare providers can perform a quick screening on nearly every infant before hospital discharge, allowing for the early identification of those at risk. This immediate assessment reduces the need for frequent, painful heel-pricks and unnecessary blood draws. Universal screening with POCT devices also helps reduce hospital readmissions for severe hyperbilirubinemia by enabling earlier treatment.
POCT measurements provide an objective, reliable alternative to the subjective visual assessment of jaundice, which is often unreliable, particularly in infants with darker skin tones. By providing a numerical value, the device helps clinicians track the bilirubin trend over the first few days of life. This allows for the timely initiation of phototherapy, which uses blue light to convert bilirubin into an easily excretable form, preventing progression to dangerous levels.
Comparing POCT to Laboratory Analysis
Point-of-care bilirubinometry complements the traditional, centralized laboratory analysis of Total Serum Bilirubin (TSB). TSB measurement is the gold standard for definitive diagnosis, analyzing a blood sample using high-precision laboratory analyzers. These lab tests require a blood draw and have a turnaround time ranging from minutes to hours. In contrast, POCT offers near-instantaneous results directly at the patient’s bedside.
The primary trade-off lies in precision and clinical role. POCT devices offer convenience and speed but are generally considered screening tools, not diagnostic confirmations. Non-invasive transcutaneous devices may sometimes underestimate the true TSB level, particularly when bilirubin concentration is very high or if the patient is receiving phototherapy.
The clinical workflow uses POCT results to decide whether a blood draw is necessary. If the transcutaneous reading is below a certain threshold, it is sufficient for monitoring. However, if the reading approaches or exceeds a predetermined treatment level, a confirmatory TSB blood sample must be sent to the central laboratory. This tiered approach leverages the speed and comfort of POCT for screening while relying on the superior accuracy and precision of the laboratory method for making treatment decisions.