Urine Metabolite Analysis to Identify Pathomechanisms of Long COVID: A Pilot Study.
Taenzer, Maja, Löffler-Ragg, Judith, Schroll, Andrea et al. · International journal of tryptophan research : IJTR · 2023 · DOI
Quick Summary
This study examined urine samples from people with Long COVID and ME/CFS to look for chemical imbalances that might explain their symptoms. Researchers found that both groups had lower levels of certain amino acids and neurotransmitters (brain chemicals) compared to healthy people, particularly affecting energy production, mood, and sleep. These chemical signatures could potentially be used as simple urine tests to help doctors understand what is happening in patients and create personalized treatments.
Why It Matters
Finding measurable biomarkers in urine is crucial for ME/CFS patients because routine blood tests often appear normal despite significant illness. These results suggest that urine metabolite analysis could provide an accessible, objective way to identify underlying biological mechanisms and potentially guide personalized treatment decisions for both Long COVID and ME/CFS.
Observed Findings
Phenylalanine levels were significantly lower in both Long COVID and ME/CFS groups compared to healthy controls.
Downstream metabolites of tryptophan and tyrosine (including serotonin, dopamine, and catecholamines) showed abnormal concentrations in many Long COVID patients.
Patients with fatigue had significantly reduced kynurenine, phenylalanine, and a reduced kynurenine-to-tryptophan ratio.
Patients with anxiety showed lower GABA concentrations and higher kynurenine 3-monooxygenase (KMO) activity.
Metabolite dysregulations were associated with specific symptoms including sleep disturbance, pain, and autonomic dysfunction.
Inferred Conclusions
Amino acid metabolism and neurotransmitter synthesis pathways are disturbed in both Long COVID and ME/CFS patients.
Identified metabolites could serve as potential urine biomarkers for distinguishing different underlying pathomechanisms within these patient populations.
Metabolite-symptom associations suggest that personalized treatment strategies targeting specific dysregulated pathways may be feasible.
Remaining Questions
Can these urine metabolite signatures reliably distinguish ME/CFS/Long COVID subtypes in larger, more diverse patient populations?
What This Study Does Not Prove
This pilot study does not prove that these metabolite changes cause ME/CFS or Long COVID symptoms—it only shows associations in a small sample. The cross-sectional design cannot establish whether metabolite abnormalities precede symptoms, result from them, or are consequences of illness behavior. Larger longitudinal studies are needed to determine causality and whether correcting these metabolites improves symptoms.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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Do these metabolite abnormalities precede symptom onset, or are they secondary consequences of the illness?
Would correcting these identified metabolite imbalances actually improve patient symptoms and functional capacity?
How do these metabolic dysregulations relate to other proposed Long COVID/ME/CFS mechanisms such as autonomic dysfunction, inflammation, and gut dysbiosis?