Table 2.
Candidate biochemical biomarkers investigated in at least two studies, with at least one positive finding and more than 50% frequency of replication, for autism spectrum disorder
| Biomarker | Number of studies with significant finding | Number of studies with non‐significant finding | Direction | Frequency of replication (%) |
|---|---|---|---|---|
| 2‐aminobutyric acid (urine, plasma) | 2 | 0 | Increased | 100 |
| 2‐hydroxybutyric acid (urine) | 2 | 0 | Increased | 100 |
| 8‐isoprostane (urine, plasma) | 3 | 0 | Increased | 100 |
| Adrenic acid (plasma) | 2 | 0 | Decreased | 100 |
| Alanine (urine, serum) | 2 | 0 | Decreased | 100 |
| Alpha‐1‐antitrypsin (plasma) | 2 | 0 | Increased | 100 |
| Anandamide (serum, plasma) | 2 | 0 | Decreased | 100 |
| Arachidic acid (serum, plasma) | 2 | 0 | Increased | 100 |
| Aspartic acid (urine, plasma) | 2 | 0 | Decreased | 100 |
| Parabacteroides (gut microbiota) | 2 | 0 | Increased | 100 |
| Creatine kinase (serum, urine) | 2 | 0 | Increased | 100 |
| Coproporphyrin (urine) | 4 | 0 | Increased | 100 |
| Cysteine (serum, plasma, urine) | 3 | 0 | Decreased | 100 |
| Glutamine (blood, serum) | 4 | 0 | Decreased | 100 |
| Glutathione/oxidized glutathione ratio (serum) | 3 | 0 | Decreased | 100 |
| High‐density lipoprotein (serum) | 2 | 0 | Decreased | 100 |
| Hippuric acid (urine) | 2 | 0 | Increased | 100 |
| High‐sensitivity C‐reactive protein (serum) | 2 | 0 | Increased | 100 |
| Heat shock protein 70 (serum, plasma) | 2 | 0 | Increased | 100 |
| Interferon‐gamma‐inducible protein 16 (serum) | 2 | 0 | Increased | 100 |
| Kynurenic acid (serum, urine) | 2 | 0 | Decreased | 100 |
| Lactic acid (urine) | 2 | 0 | Increased | 100 |
| Lead (urine, hair, red blood cells) | 3 | 0 | Increased | 100 |
| Neurotensin (serum) | 3 | 0 | Increased | 100 |
| Para‐cresol (urine) | 3 | 0 | Increased | 100 |
| Peroxiredoxin 1 (serum, plasma) | 2 | 0 | Increased | 100 |
| Phosphatidylcholine (serum) | 2 | 0 | Decreased | 100 |
| Pregnenolone sulfate (plasma) | 2 | 0 | Decreased | 100 |
| Secreted amyloid precursor protein alpha (plasma) | 3 | 0 | Increased | 100 |
| Succinic acid (urine, plasma) | 3 | 0 | Increased | 100 |
| Transforming growth factor beta (serum, blood) | 3 | 0 | Increased | 100 |
| Thiol (serum, urine) | 2 | 0 | Decreased | 100 |
| Triglycerides (plasma) | 2 | 0 | Increased | 100 |
| Gamma‐aminobutyric acid (blood, plasma, serum) | 7 | 0 | Six increased, one decreased | 85 |
| Melatonin (serum, plasma, urine) | 5 | 0 | One increased, four decreased | 80 |
| Dopamine (plasma, blood) | 4 | 0 | Three increased, one decreased | 75 |
| Glial fibrillary acidic protein (serum) | 3 | 1 | Increased | 75 |
| Glutathione (serum, plasma) | 7 | 1 | One increased, six decreased | 75 |
| Potassium (serum) | 4 | 0 | One increased, three decreased | 75 |
| Leucine (serum) | 3 | 0 | Two increased, one decreased | 67 |
| Sodium (serum, plasma) | 3 | 0 | Two increased, one decreased | 67 |
| Antioxidant capacity (urine) | 3 | 0 | Two decreased, one increased | 67 |
| Arginine vasopressin (cerebrospinal fluid) | 2 | 1 | Decreased | 67 |
| Catalase (urine, plasma) | 2 | 1 | Increased | 67 |
| Citric acid (urine, plasma) | 3 | 0 | Two increased, one decreased | 67 |
| Citrulline (blood, urine) | 2 | 1 | Increased | 67 |
| Docosahexaeonic acid/arachidonic acid (plasma) | 2 | 1 | Increased | 67 |
| Epidermal growth factor (plasma) | 2 | 1 | Decreased | 67 |
| Epinephrine (plasma, blood, gut metabolites) | 3 | 0 | Two increased, one decreased | 67 |
| Glutamate (serum, blood) | 2 | 1 | Increased | 67 |
| Hexanol‐lysine (urine) | 2 | 1 | Increased | 67 |
| Hypoxanthine (urine) | 2 | 1 | Increased | 67 |
| Interleukin‐17‐A (plasma, serum) | 2 | 1 | Increased | 67 |
| Indole‐3‐acetic acid (urine) | 2 | 1 | Increased | 67 |
| Oxalic acid (urine) | 2 | 1 | Increased | 67 |
| Oxidized glutathione (plasma) | 2 | 1 | Increased | 67 |
| Pentacarboxyporphyrin (urine) | 2 | 1 | Increased | 67 |
| Phosphoric acid (urine) | 2 | 1 | Decreased | 67 |
| S100 calcium‐binding protein B (serum, plasma) | 4 | 2 | Increased | 67 |
| Tumor necrosis factor‐alpha (saliva, serum) | 2 | 1 | Increased | 67 |
| Thyroid stimulating hormone (serum) | 2 | 1 | Decreased | 67 |
| Uric acid (serum, urine) | 3 | 0 | Two increased, one decreased | 67 |
| Vitamin E (plasma) | 2 | 1 | Decreased | 67 |
| Glutathione S‐transferase (serum, plasma) | 3 | 0 | One increased, two decreased | 67 |
| Brain‐derived neurotrophic factor (serum, plasma, blood) | 9 | 1 | Six increased, three decreased | 67 |
| Cortisol (saliva, plasma, gut metabolites) | 3 | 2 | Increased | 60 |
| Eicosapentaenoic acid (serum) | 3 | 2 | Increased | 60 |
| Ferritin (serum) | 3 | 2 | Decreased | 60 |
| Homocysteine (serum, urine, plasma) | 9 | 1 | Six increased, three decreased | 60 |
| Interleukin‐8 (serum, plasma) | 6 | 4 | Increased | 60 |
| Creatinine (urine) | 4 | 3 | Increased | 57 |
| Mercury (blood cells, serum, urine, hair) | 4 | 3 | Increased | 57 |
| Interleukin‐1‐beta (plasma) | 7 | 4 | Six increased, one decreased | 54 |