| Cause | Ammonia | Acid-Base Status | Anion Gap | Ketones in Urine | Distinctive Features |
|---|---|---|---|---|---|
| Urea Cycle Defects (UCDs) | ↑ | No acidosis; may have alkalosis | Normal | Absent | Respiratory alkalosis; normal glucose; no ketones |
| Fatty Acid Oxidation (FAO) Disorders | ↑ | Metabolic acidosis | ↑ | Absent | Hypoglycemia with low ketones despite fasting |
| Organic Acidemias | ↑ | Metabolic acidosis | ↑ | ↑ | Elevated lactate; abnormal organic acids in urine |
| Transient Hyperammonemia of the Newborn | ↑ | Variable | Normal or mildly ↑ | Variable | Premature infants; rapid postnatal neurological decline |
| Reye’s Syndrome | ↑ | Variable | Normal or ↑ | Variable | Hypoglycemia and coagulopathy after viral illness or aspirin use |
| Liver Failure | ↑ | Variable | Normal or ↑ | Variable | Elevated transaminases; encephalopathy; coagulopathy |
| Severe Systemic Illness | ↑ | Variable | Variable | Variable | Multiorgan dysfunction; sepsis-related metabolic derangements |
| Pyruvate Carboxylase Deficiency | ↑ | Lactic acidosis | ↑ | Variable | ↓ Aspartate, ↑ Alanine; neurodevelopmental delay |
| Lysinuric Protein Intolerance | ↑ (postprandial) | Variable | Normal or ↑ | ↑ urine amino acids | ↓ Lysine, arginine, ornithine; vomiting after protein intake |
| Drugs (Valproate, Cyclophosphamide) | ↑ | Variable | Normal or ↑ | Variable | Valproate: ↓ carnitine; hepatotoxicity; altered mental status |