TWO YEARS EXPERIENCE OF ANALYTICAL AND DIAGNOSTIC CHALLENGES IN URINE ORGANIC ACID ANALYSIS ON GAS CHROMATOGRAPHY-MASS SPECTROMETRY
Analytical and Diagnostic Challenges in Urine Organic Acid Analysis
Keywords:Gas chromatography-Mass spectrometry, Inherited metabolic disorders, Organic aciduria
Objective: To evaluate the analytical and diagnostic challenges in interpreting the various organic acid results by
gas-chromatography-mass spectrometry and to devise a protocol for analysis that is beneficial for prompt
interpretation and diagnosis.
Study Design: Retrospective study.
Place and Duration of Study: Department of Chemical Pathology & Endocrinology, Armed Forces Institute of
Pathology, Rawalpindi, from Apr 2015 to May 2017.
Material and Methods: We reviewed clinical data, biochemical investigations and urine organic acid profiles of
110 patients received for evaluation of a suspected organic acid disorder. Urine organic acid analysis was carried
out by gas chromatography – mass spectrometry using Mass Hunter software.
Results: A total of 104 (99%) cases received were from the pediatric patients and 7 (6.3%) from adult patients.
A total of 11 different organic acidurias were diagnosed. Other diseases (n=10) were also detected on the basis
of their pathognomics metabolites and included tyrosinemia type 1 (n=4), alkaptonuria (n=5) and ornithine
transcarbamoylase deficiency (n=1). Twenty-eight (25%) urine samples were either recalled or repeated for
reasons like random urine sample yielding negative profiles in setting of a strong suspicion for organic aciduria
(n=6), non-availability of clinical data (n=12) or delay in transportation >8 hours (n=10). Raised non-specific
organic acid metabolites were seen in 23 (21%) cases. Lactic acid and ketones were detectable in 12 (11%) samples
in the absence of raised plasma levels.
Conclusion: Urine OA profiles must be interpreted in context of complete clinical, nutritional and biochemical
findings. Each laboratory equipped with this facility should devise their analytical protocols for meaningful
interpretation of results.