Bilirubin Interference in Plasma Amino Acid Analysis by Ion Exchange Chromatography

To evaluate the effect of bilirubin interference on plasma amino acid analysis by Ion Exchange Chromatography (IEC).

Cross-sectional (method validation) study.

Department of Chemical Pathology and Endocrinology, Armed Forces Institute of Pathology, Rawalpindi from August 2016 to July 2017.

Twenty non-icteric samples from paediatric patients were collected in lithium heparin tubes and analysed for amino acids on IEC-based Biochrome® 30+ Analyzer (Harvard Biosciences UK). Baseline bilirubin levels were noted. Samples were spiked with neonatal bilirubin standard with concentration of 488.4 mol/L (Spinreact®-Spain) at final concentrations of 50, 150 and 230 mol/L and re-analysed for amino acids at these three concentrations.

Among the 20 selected patients with normal amino acid profiles, 12 (60%) were males. Majority (55%) were in age group of 1-5 years. Significant difference was observed for Arginine (p = 0.01), Histidine (p = 0.001), Isoleucine (p = 0.01), Leucine (p = 0.007), Lysine (p = 0.005), Ornithine (p = 0.03) and Phenylalanine (p = 0.02). Mean rank of these amino acids showed decreasing trend with the increase of bilirubin concentration, and pronounced interference was identified at bilirubin level of 50 mol/L. No difference was observed for alanine, citrulline, glutamic acid, glycine, methionine, proline, threonine, tyrosine, asparagine, aspartic acid, cystine, valine and tryptophan.

Bilirubin significantly interferes with certain amino acid levels when analysis is carried out by ion exchange chromatography. A close follow-up of such patients with other biochemical tests and a repeat amino acid analysis, after jaundice is settled, is recommended to confidently rule out any possible inherited metabolic disorder in these patients.