Background: Alkaptonuria is a rare autosomal recessive disorder. Due to a deficiencyofthe enzyme, homogentisic acid oxidase, homogentisic acid (HGA) cannot be furthermetabolized resulting in accumulation of HGA and its oxidative metabolites inblood, connective tissue and urine, causing a triad of homogentisic aciduria, ochronosis and arthritis. Although the metabolic defect is present from birth, diagnosis is frequently delayeduntil adulthood, when patients develop ochronosis and degenerative arthropathy. Early diagnosisduring infancy is uncommon, particularly in low-resource settings where access tospecialized metabolic investigations is limited.

Case Presentation: A one-year-old boy, born to non-consanguineous parents, presentedwith a history of black discoloration of urine-soaked nappies when left unwashed for several hours. Despite multiple medical evaluations, the underlying cause remained undetermined. The child was otherwise healthy, with normal growth and development. Freshly voidedurineappeared normal but gradually turned dark brown to black on prolonged exposuretoatmosphere. The results of the routine laboratory investigations were unremarkable. However, simple qualitative biochemical tests performed in the clinical chemistry laboratory, includingBenedict test and ammoniacal silver nitrate test, suggested the presence of HGAin urine. Thediagnosis was subsequently confirmed by semi-quantitative urinary organic acid analysisusing gas chromatography–mass spectrometry, which demonstrated markedly elevatedurinary HGA. The child was commenced on ascorbic acid therapy, advised on dietaryproteinmoderation, and enrolled for long-term follow-up.

Conclusion: This case highlights that clinical observation, combined with inexpensivequalitative biochemical tests, can facilitate the early diagnosis of alkaptonuria eveninresource-constrained settings. Recognition of characteristic urine discoloration andtheappropriate use of basic laboratory investigations can enable timely diagnosis, avoidunnecessary investigations, allow appropriate genetic counselling, and facilitate earlymonitoring before irreversible complications develop. Increased awareness among cliniciansand laboratory professionals is essential to reduce diagnostic delays for this rare but readilyrecognizable inherited metabolic disorder.

Dilanthi Hewa Warawitage, MBBS, Dip Chem Path, MD (Chemical Pathology), SEDA(UK), is a Specialist in Chemical Pathology and Senior Lecturer at the Faculty of Medicine, University of Colombo, Sri Lanka. She obtained her MD from the Postgraduate InstituteofMedicine, Colombo with clinical training at Lady Ridgeway Hospital for Children, Colombo, which is the national referral center for paediatric care. She has served as an HonoraryRegistrar in Clinical Biochemistry at Monash Medical Centre, Melbourne, Australia. Heracademic interests include inborn errors of metabolism, metabolic disorders and biomarkerresearch, with publications in national and international journals. She is an Associate Editorof the Annals of Clinical Biochemistry and a council member of the College of Chemical Pathologists of Sri Lanka