Ammonia (NH₃) Unit Converter
Ammonia (NH₃) Unit Converter
Convert plasma ammonia between µg/dL, µmol/L and µg/L, with the sampling rules that determine whether the result means anything.
Ammonia (NH₃) converter
Mass ⇄ molarAmmonia 75 µg/dL
Formula and conversion factor
µg/dL = µmol/L ÷ 0.5872
- 0.5872
- derived from the molecular weight of ammonia, 17.031 Da
- ammonia nitrogen
- some laboratories report nitrogen rather than ammonia; the factor is then 0.714 and the two are not interchangeable
- µg/L
- µg/dL × 10
Worked example
Ammonia 75 µg/dL
75 × 0.5872 = 44.0 µmol/L
= 750 µg/L
Pre-analytical requirements
| Step | Requirement | Effect if missed |
|---|---|---|
| Tourniquet | Avoid, or release before drawing | Muscle ammonia release raises the result |
| Fist clenching | Avoid | Raises the result |
| Transport | On ice, immediately | Ammonia rises in the tube over minutes |
| Separation | Within 30 minutes | Continued generation from red cells |
| Smoking | Avoid before sampling | Raises the result |
What ammonia measures, and what it does not
Ammonia is produced by gut bacteria and by amino acid metabolism, and is cleared by hepatic conversion to urea. It accumulates when hepatic clearance fails, when blood bypasses the liver through portosystemic shunts, or when a urea cycle enzyme is deficient.
Its role in hepatic encephalopathy is more limited than commonly assumed. Ammonia correlates poorly with the grade of encephalopathy in chronic liver disease, and both normal levels in encephalopathic patients and raised levels in lucid ones are common. Guidelines are consistent that hepatic encephalopathy is a clinical diagnosis and that ammonia should not be used to make it, to grade it, or to follow treatment response.
Where it genuinely earns its place is in acute liver failure, where a very high arterial ammonia predicts cerebral oedema and intracranial hypertension, and in the investigation of unexplained encephalopathy where a urea cycle disorder or valproate toxicity is possible. In those settings a normal ammonia is genuinely informative.
Pre-analytical handling dominates the result. A tourniquet, a clenched fist, a delay in transport or separation, or a smoker before the draw will all raise it, and a spuriously high value that changes management is a real and frequent harm.
Frequently asked questions
How do I convert ammonia from µg/dL to µmol/L?
Multiply by 0.587. An ammonia of 75 µg/dL is 44 µmol/L. Check first whether your laboratory reports ammonia or ammonia nitrogen — the nitrogen factor is 0.714 and mixing them gives a wrong answer.
Is ammonia useful in hepatic encephalopathy?
Not for diagnosis or grading in chronic liver disease, where it correlates poorly with clinical state. Guidelines advise against using it to make the diagnosis. It is genuinely useful in acute liver failure and in suspected urea cycle disorders.
Why must the sample go on ice?
Ammonia is generated in the tube by red cell metabolism and amino acid breakdown, so the measured value climbs with time at room temperature. Transport on ice and separate within 30 minutes.
Can a tourniquet raise ammonia?
Yes. Muscle releases ammonia during stasis and fist clenching, which is a common cause of a spuriously high result. Draw without a tourniquet where possible.
Related calculators
References
- Vilstrup H et al. Hepatic encephalopathy in chronic liver disease: 2014 practice guideline by AASLD and EASL. Hepatology. 2014;60(2):715–35.
- Barsotti RJ. Measurement of ammonia in blood. J Pediatr. 2001;138(1 Suppl):S11–20.