Organic Acids Test (OAT) — Comprehensive Urine Metabolic Profile (Mosaic Diagnostics)

The tricarboxylic acid (Krebs) cycle is the central metabolic hub of oxidative phosphorylation — a series of eight enzymatic reactions occurring in the mitochondrial matrix that complete the oxidation of acetyl-CoA derived from carbohydrate, fatty acid, and amino acid catabolism, generating NADH and FADH2 for the electron transport chain. TCA cycle intermediates — citrate, isocitrate, alpha-ketoglutarate, succinate, fumarate, malate, and oxaloacetate — are excreted in urine in small but measurable quantities. Abnormal patterns of TCA intermediate excretion reflect mitochondrial enzyme dysfunction, electron transport chain impairment, substrate delivery defects, or cofactor deficiencies affecting TCA cycle enzyme activity — particularly thiamine (B1, cofactor for pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase), riboflavin (B2, FAD-dependent succinate dehydrogenase), and alpha-lipoic acid.

Elevation of specific TCA intermediates provides evidence of mitochondrial metabolic dysfunction at identifiable enzymatic steps. Elevated succinic acid suggests succinate dehydrogenase impairment — relevant in SDH-related paraganglioma/phaeochromocytoma and mitochondrial complex II deficiency. Elevated alpha-ketoglutaric acid with pyruvic acid suggests pyruvate dehydrogenase or alpha-ketoglutarate dehydrogenase dysfunction — associated with thiamine deficiency, lipoic acid deficiency, or mitochondrial disease. In functional and integrative medicine, mild TCA intermediate elevations are interpreted as evidence of mitochondrial metabolic stress — guiding nutritional cofactor support (B vitamins, alpha-lipoic acid, CoQ10, carnitine) in patients with fatigue, cognitive impairment, and reduced exercise tolerance.

Pyruvate and lactate are the terminal products of glycolysis and the entry point to mitochondrial oxidative metabolism via pyruvate dehydrogenase complex (PDC). The lactate:pyruvate ratio reflects the cytoplasmic NADH:NAD+ redox status — elevated ratios indicate impaired NAD+ regeneration consistent with electron transport chain dysfunction or oxygen deficit. Medium-chain fatty acid oxidation generates dicarboxylic acids (adipic, suberic, sebacic acid) as urinary byproducts through omega-oxidation when beta-oxidation is saturated or impaired. Elevated medium-chain dicarboxylates signal fatty acid oxidation defects — MCAD deficiency is the most clinically important — or high-fat metabolic states. 3-hydroxybutyric acid (BOHB) is the primary ketone body marker, elevated in fasting, ketogenic dietary states, and diabetic ketoacidosis.

In the OAT clinical context, energy production markers characterise the efficiency of the primary ATP-generating metabolic pathways. Elevated pyruvate and lactate with normal lactate:pyruvate ratio suggests increased glycolytic flux from high carbohydrate intake or metabolic stress. Elevated lactate:pyruvate ratio (above 20:1) indicates NADH-NAD+ imbalance consistent with mitochondrial respiratory chain dysfunction and warrants metabolic specialist evaluation. Elevated dicarboxylic acids suggest medium-chain fatty acid oxidation impairment — MCAD deficiency is the most prevalent inborn error of metabolism in populations of Northern European descent and is potentially life-threatening during metabolic stress without early intervention. In functional medicine, mildly elevated dicarboxylates in adults are interpreted as evidence of partial fatty acid oxidation impairment amenable to riboflavin, carnitine, and CoQ10 support.

Urinary organic acid metabolites serve as functional downstream indicators of cofactor adequacy — rising when B-vitamin-dependent enzymatic reactions are impaired. Methylmalonic acid (MMA) rises when adenosylcobalamin (B12 mitochondrial cofactor) is insufficient, impairing methylmalonyl-CoA mutase — providing earlier evidence of functional B12 deficiency than serum B12 alone. Xanthurenate and kynurenate — tryptophan catabolism byproducts — accumulate when pyridoxal-5-phosphate (active B6) is insufficient for kynureninase activity, providing a functional marker of B6 status. Pantothenate deficiency impairs CoA synthesis, affecting multiple acetylation reactions. These metabolic downstream markers provide functional evidence of cofactor inadequacy at the cellular level — often preceding detectable changes in serum vitamin concentrations.

The B-vitamin functional marker group is among the highest-yield sections of the OAT in integrative clinical practice. Elevated MMA on the OAT confirms functional intracellular B12 deficiency — more sensitive and specific than serum B12 for detecting cellular cobalamin insufficiency, and actionable for methylcobalamin or hydroxocobalamin supplementation. Elevated xanthurenate and kynurenate confirm functional B6 insufficiency — clinically relevant for neurotransmitter synthesis (B6 is a cofactor for serotonin, dopamine, GABA synthesis), cardiovascular risk (B6 is required for homocysteine remethylation), and immune function. The OAT therefore provides a panel-wide nutritional status assessment that extends and corroborates single-analyte serum vitamin measurements.

Urinary neurotransmitter catabolites provide metabolic evidence of monoamine and tryptophan pathway activity downstream of central and peripheral synthesis. HVA is the terminal dopamine metabolite — produced by sequential MAO-A and COMT catabolism — excreted primarily renally; it reflects combined central and peripheral dopamine catabolism rather than synaptic dopamine activity directly. 5-HIAA is the terminal serotonin metabolite via MAO-A — its urinary elevation is diagnostically established for carcinoid tumour and neuroendocrine tumour secreting serotonin, and in functional medicine is used as a proxy for peripheral serotonin turnover and tryptophan flux. Quinolinic acid and kynurenic acid are produced through the kynurenine pathway — the major metabolic route for dietary tryptophan (approximately 95% of tryptophan). Quinolinic acid is an NMDA receptor agonist and neurotoxin produced by activated microglia and macrophages; elevated urinary quinolinic acid is a marker of neuroimmune activation, tryptophan pathway dysregulation, and excitotoxic burden.

In the OAT clinical context, neurotransmitter metabolites characterise the downstream catabolism of monoamine pathways, provide tryptophan pathway metabolic characterisation, and screen for neuroendocrine tumours. Markedly elevated 5-HIAA (above 10× the upper reference limit) in a non-dietary context warrants carcinoid/neuroendocrine tumour evaluation — the OAT is not a validated diagnostic test for carcinoid, but incidental extreme 5-HIAA elevation should prompt clinical follow-up. In functional medicine, HVA:5-HIAA ratio is used to assess the relative balance of dopaminergic and serotonergic catabolism, guiding amino acid precursor support decisions. Elevated quinolinic acid with low kynurenic acid indicates a pro-inflammatory, pro-excitotoxic tryptophan pathway shift — associated with neuroinflammation, depression, chronic fatigue, and cognitive impairment in functional medicine frameworks. # REVIEWER FLAG: The clinical utility of urinary HVA and 5-HIAA as surrogate markers of CNS monoamine activity is limited by the blood-brain barrier — urinary metabolites predominantly reflect peripheral catabolism. Reviewer to confirm appropriate interpretive framing.

Oxalate is a metabolic end-product arising from multiple precursors — glyoxylate (via alanine-glyoxylate aminotransferase, AGT, in the peroxisome), ascorbate oxidation, hydroxyproline catabolism, and dietary oxalate absorption. The liver is the primary site of oxalate synthesis, with the kidneys excreting it exclusively — renal oxalate accumulation forms calcium oxalate crystals responsible for the majority of renal stones. Primary hyperoxalurias (PH1, PH2, PH3) are rare genetic enzyme defects producing severe urinary oxalate elevation. Secondary hyperoxaluria arises from malabsorption states (enteric hyperoxaluria from fat malabsorption increasing gut oxalate absorption), high-dose vitamin C supplementation (ascorbate-to-oxalate conversion), or high-oxalate dietary intake.

Urinary oxalate within the OAT provides a non-invasive screen for both primary and secondary hyperoxaluria — the leading biochemical cause of nephrolithiasis and a contributor to chronic kidney injury in severe cases. In functional medicine, elevated urinary oxalate is assessed as a potential contributor to pain syndromes (vulvodynia, fibromyalgia, joint pain), kidney stone recurrence risk, and mitochondrial function impairment from calcium oxalate crystal formation in tissues. Elevated urinary oxalate should prompt dietary oxalate assessment, B6 status evaluation (PLP is the AGT cofactor whose deficiency impairs glyoxylate detoxification), vitamin C supplementation review, and gut microbiome assessment for Oxalobacter formigenes colonisation (which degrades intestinal oxalate). Glycolic acid elevation alongside oxalate elevation may indicate PH1 (AGT deficiency) — paediatric metabolic specialist referral is warranted for extreme elevations in children.

Intestinal microorganisms produce characteristic metabolites that are absorbed from the gut, metabolised, and excreted in urine as organic acids measurable by GC-MS. Arabinitol and arabinose are produced by Candida species and certain other yeasts through pentose pathway fermentation; their urinary elevation is a marker of intestinal or systemic yeast overgrowth. Dihydroxyphenylpropionic acid (DHPPA) is produced by Clostridia species through tyrosine fermentation and inhibits dopamine beta-hydroxylase — its elevation has been proposed as a marker of Clostridium overgrowth contributing to neurobehavioural symptoms through dopamine pathway interference. Tricarballylic acid is produced by Fusarium species — commonly associated with mycotoxin co-production. These microbial metabolites are absorbed through the intestinal wall and reach the kidney for urinary excretion, providing an indirect metabolic reflection of intestinal microbial population composition.

The intestinal microbial markers section is the most widely discussed and clinically applied component of the OAT in functional and integrative medicine, and simultaneously the section with the most evidence-grade caveats. Elevated arabinose/arabinitol is interpreted as supportive evidence of intestinal Candida or yeast overgrowth — guiding antifungal therapy decisions in the integrative clinical context. Elevated DHPPA is used in functional medicine as a marker of Clostridium overgrowth contributing to neurobehavioural dysfunction. These interpretations are clinically actionable within the Mosaic Diagnostics functional framework but are not validated by prospective clinical trials, randomised controlled evidence, or mainstream gastroenterology guidelines. Practitioners using the microbial markers section for clinical decision-making should communicate the evidence-base context clearly to patients and document the interpretive framework applied. # REVIEWER FLAG: The clinical validity of urinary arabinose as a Candida overgrowth diagnostic marker is contested in mainstream gastroenterology and infectious disease — arabinose has other dietary and metabolic sources. Reviewer to confirm appropriate evidence-grade framing for this platform's practitioner audience.

Amino acid catabolism generates characteristic organic acid intermediates whose urinary excretion reflects the functional activity of specific aminotransferase and oxidase enzymes, many of which are vitamin B-dependent. Phenylpyruvic acid and phenyllactic acid accumulate when phenylalanine hydroxylase (PAH) activity is impaired — the basis of phenylketonuria (PKU) screening. Succinylacetone accumulation indicates fumarylacetoacetate hydrolase deficiency (hereditary tyrosinaemia type 1 — a neonatal emergency). Glutaric acid with 3-hydroxyglutaric acid signals glutaryl-CoA dehydrogenase deficiency (glutaric aciduria type 1). These amino acid metabolite markers in the OAT serve both as inherited metabolic disease screening tools — complementing newborn screening panels in patients with undiagnosed presentations — and as acquired cofactor-deficiency indicators in functional medicine contexts.

In the adult OAT, severely elevated amino acid metabolites that would indicate the classical inborn errors of metabolism (PKU, tyrosinaemia, glutaric aciduria) are typically already identified through neonatal screening. However, partial enzyme deficiencies, late-presenting attenuated variants, and acquired cofactor-related metabolic disturbances may produce mild-to-moderate elevations detectable on the OAT. In functional medicine, elevated phenylalanine or tyrosine-derived metabolites guide neurotransmitter precursor and cofactor support. Elevated methylsuccinic acid and ethylmalonic acid in the organic acid profile suggest branched-chain amino acid catabolism impairment and short-chain fatty acid oxidation dysfunction relevant to riboflavin and CoQ10 supplementation protocols.

8-hydroxy-2-deoxyguanosine (8-OHdG) is a ubiquitous oxidative DNA damage product — formed when reactive oxygen species (ROS) attack the guanine base of DNA — repaired by base excision repair and excreted in urine. Urinary 8-OHdG is the most widely validated urinary oxidative stress biomarker across epidemiological research and is elevated in cancer, cardiovascular disease, neurodegenerative conditions, diabetes, and chronic infection. Pyroglutamic acid (5-oxoproline) is an intermediate in the gamma-glutamyl cycle — elevated urinary pyroglutamic acid indicates glutathione depletion (increased demand driving the cycle) or gamma-glutamyl synthetase deficiency. HMG-CoA pathway intermediates reflect mevalonate pathway activity and statin-associated CoQ10 depletion when elevated.

The oxidative stress markers in the OAT provide an integrated picture of systemic oxidative burden and antioxidant reserve status — particularly glutathione cycle function — that complements individual antioxidant measurements (serum vitamin C, vitamin E, selenium). Elevated 8-OHdG guides antioxidant support intervention and can serve as a monitoring marker for oxidative stress reduction from dietary, lifestyle, and supplementation interventions over serial OAT assessments. Elevated pyroglutamic acid in a patient with fatigue and immune dysfunction suggests glutathione depletion warranting N-acetylcysteine (NAC), glycine, and glutamine precursor support. In the context of statin therapy, elevated methylglutaric acid and HMG-related metabolites may indicate statin interference with the mevalonate pathway affecting CoQ10 production — guiding CoQ10 supplementation recommendations in symptomatic patients on statins.

The remaining OAT analytes provide supplementary metabolic characterisation spanning renal tubular function (phosphate excretion), carbohydrate metabolism, and miscellaneous cofactor pathway markers. Phosphoric acid excretion reflects renal tubular phosphate reabsorption — elevated urinary phosphate alongside low serum phosphate suggests proximal tubular dysfunction (Fanconi syndrome) from cadmium toxicity, Lowe syndrome, or tenofovir nephrotoxicity.

These supplementary markers complete the OAT's comprehensive metabolic profile, providing additional diagnostic sensitivity for rare metabolic conditions, renal tubular dysfunction, and nutritional imbalances not captured by the primary analyte sections. Their interpretation is integrated with the full OAT picture rather than assessed in isolation.