LC-MS-Based Simultaneous Determination of Biomarkers in Dried Urine Spots for the Detection of Cofactor-Dependent...

Deficiency of cofactors for various enzymes can lead to inborn errors of metabolism. These conditions frequently occur as seizures, which lead to permanent brain damage. Newborn screening for biomarkers associated with these disorders can help in early detection and treatment. Our objective was to establish a liquid chromatography mass spectrometry technique for quantifying biomarkers in dried urine spots to detect specific vitamin-responsive inborn errors metabolism. Biomarkers were extracted from dried urine spots using a methanol:0.1% v/v formic acid solution (75:25) containing an internal standard mixture. Separation was achieved using a Luna PFP column (150 mm × 4.6 mm, 3 µm) under gradient elution conditions. The LC-MS technique was validated as per ICH M10 guidelines. Urine samples from healthy newborns in Udupi district, South India, were analyzed to establish reference values for these biomarkers. The method demonstrated excellent linearity (R² > 0.99) with low limits of quantification: 0.1 µg/mL for leucine, isoleucine, valine, proline, hydroxyproline, methylmalonic acid, and 3-hydroxyisovaleric acid; 0.01 µg/mL for pipecolic acid and α-aminoadipic semialdehyde; and 0.03 µg/mL for piperideine-6-carboxylate. Interconvertibility between urine and dried urine spot assays was observed from the results of the regression and Bland-Altman analyses. Reference intervals for these biomarkers in the Udupi neonatal population were established using the validated dried urine spot method.