Beta-2 microglobulin-based equation for estimating glomerular filtration rates in Japanese children and adolescents

Background: Although the creatinine (Cr)-based equation is widely used for estimating glomerular filtration rate (GFR), this equation is not ideally suited for children with low body weight or aged <2 years. Therefore, we established a new equation using serum beta-2 microglobulin (β2MG) levels for Japanese children with chronic kidney disease (CKD). Methods: Inulin clearance and standardized serum β2MG and Cr levels were measured in 137 CKD patients aged 1 month–18 years. Using the previously established normal β2MG levels, Cr reference values, and Cr-based equation of estimated GFR (eGFR) in Japanese children, receiver operating characteristics (ROC) analyses were performed to compare the diagnostic accuracy between β2MG- and Cr-based estimations of GFR. Results: Serum β2MG concentrations progressively increased as GFRs reduced. The correlation coefficients between GFR and β2MG, and between GFR and 1/β2MG were −0.74 (p < 0.001) and 0.86 (p < 0.001), respectively. The inulin clearance, as based on 1/serum β2MG expression, in pediatric CKD patients resulted in the equation: inulin GFR (mL/min/1.73 m²) = 149.0 × 1/serum β2MG (mg/L) +9.15. ROC analyses indicated that the ability of serum β2MG-based GFR <95 mL/min/1.73 m² in children >2 years was better than the Cr-based estimated GFR (areas under the ROC curve 0.960 vs. 0.948, respectively). Conclusion: The new β2MG-based eGFR formula is useful for clinical screening of renal function in Japanese children and adolescents, and measurement of serum β2MG and Cr levels as markers for predicting glomerular function may aid the early detection of mildly reduced GFR in this population.