Detection of Intravascular Hemolysis in Newborn Infants Using Urinary Carbonic Anhydrase I Immunoreactivity.

Background: Mild hemolysis occurs physiologically in neonates, but more severe forms can lead to life-threatening anemia. Newborns in developing regions are particularly at-risk due to the higher incidence of triggers (protozoan infections, sepsis, certain genetic traits). In advanced healthcare facilities, hemolysis is monitored indirectly using resource-intensive methods that probe downstream ramifications. These approaches could potentially delay critical decisions in early-life care, and are not suitable for point-of-care testing. Rapid and cost-effective testing could be based on detecting red blood cell (RBC)-specific proteins, such as carbonic anhydrase I (CAI), in accessible fluids (e.g., urine).

Methods: Urine was collected from 26 full-term male neonates and analyzed for CAI using immunoassays (ELISA, western blot) and proteomics (mass spectrometry). The cohort included a range of hemolytic states, including admissions with infection, ABO incompatibility, and receiving phototherapy. Data were paired with hemoglobin, serum bilirubin (SBR), and C-reactive protein (CRP) measurements.

Results: Urine from a control cohort (CRP < 20 mg/L, SBR < 125µmol/L) had no detectable CAI, in line with results from healthy adults. CAI excretion was elevated in neonates with raised SBR (>125 µmol/L), including those qualifying for phototherapy. Newborns with low SBR (<125 µmol/L) but elevated CRP (>20 mg/L) produced urine with strong CAI immunoreactivity. Proteomics showed that CAI was the most abundant RBC-specific protein in CAI-immunopositive samples, and did not associate with other RBC-derived peptides, indicating an intravascular hemolytic source followed by CAI-selective excretion.

Conclusions: CAI is a direct biomarker of intravascular hemolysis that can be measured routinely in urine using non-invasive methods under minimal-laboratory conditions.