The Ammonia-to-Urea Ratio Calculator is a clinical tool used to evaluate the liver’s ability to convert toxic ammonia into urea. This ratio helps diagnose conditions like hepatic encephalopathy, urea cycle disorders, and liver failure by assessing the balance between nitrogen waste production and elimination.
Definition
Ammonia-to-Urea Ratio quantifies the relationship between blood ammonia (NH₃) and urea (BUN) levels. A high ratio suggests impaired urea synthesis, often due to liver dysfunction or metabolic disorders.
Core Formula
The basic formula for the ammonia-to-urea ratio is:
Formula Variations by Units
- Using µmol/L (Ammonia) and mmol/L (Urea):
- Using µg/dL (Ammonia) and mg/dL (Urea):
🧮 Ammonia-to-Urea Ratio Calculator
📐 Formula:
Ammonia-to-Urea Ratio = Ammonia (µmol/L) ÷ Urea (mmol/L)
🖊️ Enter the Values:
Unit Conversions
| Substance | Conversion | Factor |
|---|---|---|
| Ammonia | µg/dL → µmol/L | × 0.587 |
| µmol/L → µg/dL | × 1.70 | |
| Urea | mg/dL → mmol/L | × 0.1665 |
| mmol/L → mg/dL | × 6.0 |
Step-by-Step Calculation Examples
Example 1: Using µmol/L and mmol/L
- Ammonia: 60 µmol/L
- Urea: 5 mmol/L
Example 2: Using µg/dL and mg/dL
- Ammonia: 85 µg/dL
- Urea: 15 mg/dL
- Ammonia (µmol/L)=85×0.587=49.895 μmol/L
- Urea (mmol/L)=15×0.1665=2.4975 mmol/L
Normal Values
- Ammonia:
- Adults: 15–45 µg/dL (9–27 µmol/L)
- Neonates: 64–107 µg/dL (38–64 µmol/L)
- Urea (BUN):
- Adults: 7–20 mg/dL (2.5–7.1 mmol/L)
- Ammonia-to-Urea Ratio:
- Normal: <10 (unitless)
- Elevated: ≥10 (indicates pathology)
Interpretation
- High Ratio (≥10):
- Liver dysfunction (cirrhosis, acute liver failure).
- Urea cycle disorders (genetic defects in ammonia metabolism).
- Portosystemic shunting (ammonia bypasses liver detoxification).
- Low Ratio (<10):
- Normal or increased urea production (high-protein diet, dehydration).
Clinical Relevance
- Hepatic Encephalopathy:
Elevated ammonia with a high ratio confirms impaired detoxification. - Urea Cycle Disorders:
Neonates with hyperammonemia and low urea show ratios >20. - Monitoring Therapy:
Tracks response to lactulose, rifaximin, or nitrogen scavengers.
Limitations
- Ammonia levels are labile: Affected by hemolysis, delayed processing, or exercise.
- Urea influenced by non-hepatic factors: Hydration, renal function, and diet.
- Age-dependent norms: Neonates naturally have higher ammonia levels.
Key Takeaways
- The ratio compares ammonia (toxic) to urea (non-toxic nitrogen waste).
- Normal ratio: <10; elevated values suggest liver or metabolic disease.
- Always pair with clinical context (e.g., mental status, liver enzymes).
⚠️ Disclaimer:
The content on LabTestsGuide.com is for informational and educational purposes only. We do not guarantee the accuracy, completeness, or timeliness of the information provided. Always consult qualified healthcare professionals for medical advice, diagnosis, or treatment. LabTestsGuide.com is not liable for any decisions made based on the information on this site.
