What is Ammonia Test?
An ammonia test is a test done to measure the quantity of ammonia present in the blood. Ammonia present in the body is mostly formed when there is break down of protein by the bacteria present in the intestines. The liver is the organ, which normally transforms ammonia into urea. This urea is then excreted via urine. When the liver is unable to properly convert the ammonia into urea, then this causes elevation of the ammonia level in the blood. The cause for the malfunction of the liver can be liver diseases, such as severe hepatitis or cirrhosis. The ammonia test is done by taking a blood sample from the vein or artery.
Why is the Ammonia Test done?
Given below are the reasons for doing testing for ammonia level which include:
- Checking the function of the liver, especially if the patient is having symptoms such as confusion, hand tremor, excessive sleepiness or is in a coma.
- Ammonia test is done to help in detecting Reye's syndrome, which is a childhood disorder that can damage the brain and liver. Ammonia levels can also help in predicting the prognosis (outcome) in a patient diagnosed with Reye's syndrome.
- To assess the success of treatment done for severe liver diseases, such as cirrhosis.
- Ammonia levels also help in predicting the prognosis (outcome) in a patient who has been diagnosed with acute liver failure.
- The level of ammonia is also checked in a person who is receiving high-calories intravenous nutrition.
What does the Ammonia Level indicate?
An ammonia test is done for measuring the amount of ammonia present in the blood. Results are usually available within 12 hours. Given below are some normal values for ammonia test. However, it should noted that these values are given as a reference range or as a guide. The normal values differ from one lab to another. A particular lab can have a different range for what's normal. The lab report should have the normal range, which the lab uses. Other than this, the evaluation of the results is done by the doctor based on the patient's general health and other factors.
Normal Range of Ammonia Levels
- Adults: The normal range of ammonia level in adults is 8 to 35 mcmol/L (micromoles per liter) or 9.5 to 50 mcg/dL (micrograms per deciliter).
- Children: The normal range of ammonia level in children is 28 to 58 mcmol/L or 41 to 80 mcg/dL.
- Newborns: The normal range of ammonia level in newborns is 65 to 108 mcmol/L or 91-150 mcg/dL.
High Levels of Ammonia Indicate the Following:
- Liver disease, such as hepatitis or cirrhosis.
- Reye's syndrome.
- Kidney failure.
- Heart failure.
- Extensive bleeding from the intestines or stomach.
- High levels of ammonia in a baby can occur when the blood types of the baby and the mother do not match, such as seen in hemolytic disease of the newborn.
Preparation for Ammonia Test
- It is important to abstain from smoking, eating and drinking anything other than water about 8 hours before the ammonia blood test is done.
- Strenuous exercise should be avoided before getting the ammonia test done.
- It is important to inform your doctor if you are taking any medications, as there are many medications, which can interfere with the results of the ammonia test. You may be instructed to stop certain medications for many days before getting the ammonia test.
- It is also important to talk to your doctor regarding any concerns about the test, such as the associated risks, the method of the test and the meaning of the results.
How is the Ammonia Test Done?
Venous Blood Sample
If the blood sample is taken from the vein, the medical professional will do the following:
- An elastic band is wrapped or tied around the upper arm. This will help in stopping the blood flow, so as to make the veins below the band larger, which in turn makes it easier to insert a needle into the vein.
- The needle site, from where the blood is taken, is cleaned with alcohol.
- The needle is then inserted into the vein.
- A tube is then attached to the needle which fills with blood.
- After sufficient amount of blood is collected, the elastic band is removed from the arm.
- A cotton ball or a gauze pad is applied over the needle site, as the needle is removed.
- Some pressure is applied on the needle site to halt the blood flow and then a bandage is applied.
Arterial Blood Sample
A blood sample from the artery is commonly taken from the radial artery, which is located on the inside of the wrist. Other than the radial artery, arterial blood sample can also be taken from the femoral artery, which is located in the groin or the brachial artery, which is located on the inside of the arm.
If the blood sample is taken from the artery, the medical professional will do the following:
- The patient is made to sit with his/her arm extended and the wrist is placed on a small pillow.
- The medical professional will rotate the hand back and forth in order to feel the pulse in the wrist.
- Allen test is a test done to assess if the blood circulation to the hand is adequate. This is for preventing any risk of damage to the artery of the wrist while taking the blood sample.
- Ammonia test is not done on the arm, which is used for dialysis or if there is any inflammation or infection in the region of the puncture site.
- The site of the needle is cleaned using alcohol. A local anesthetic can also be given to numb that region.
- The needle is then inserted into the artery.
- The blood is then allowed to fill the syringe. Patient should be told to breathe normally as the blood is being collected.
- A cotton ball or a gauze pad is placed over the needle site while the needle is being removed.
- A bandage is then applied over the puncture site and firm pressure is applied for about 5 to 10 minutes, or longer if the patient is having any bleeding problems or is taking any blood-thinning medicines, to halt the blood flow.
How Does it Feel When the Ammonia Test is Done?
If the blood sample is taken from a vein in the arm, patient feels a tight sensation from the elastic band wrapped around the upper arm. There may be a feeling of a quick pinch or a sting or the patient may feel absolutely nothing when the needle is being inserted.
If the blood sample is taken from an artery, then it can be painful as the arteries are situated deeper than the veins and are surrounded by nerves. Patient feels a brief, sharp pain as the needle is inserted into the artery. If the patient is given a local anesthetic, then he/she may not feel anything from the needle puncture or there may be a brief sensation of a sting or pinch as the needle pierces the skin. More pain is felt if the individual who is drawing the blood has difficulty in finding the artery or if the artery is narrowed or if the patient has increased sensitivity to pain.
Risks of Ammonia Test
Although the risk of any problems occurring is less with the ammonia test, or any type of test where a blood sample needs to be taken, patient still has to be careful with the arm or the leg from which the blood sample has been taken.
If the blood sample is taken from a vein, then there is very little risk of any problems developing. Some problems, which can develop from taking a vein blood sample include:
- There may be some bruising at the site of the needle puncture. The risk of bruising can be decreased by applying pressure on the puncture site for several minutes.
- Patients with bleeding disorders and who are on blood-thinning medicines, such as warfarin and aspirin, can have continuous bleeding. The doctor should be informed of all this before the blood sample is taken.
- Rarely, there may be swelling in the vein after the blood sample is taken. This condition is known as phlebitis. Application of warm compresses helps in treating this condition.
Patient is advised not to carry or lift objects for around 24 hours after the blood has been taken from an artery. If the blood sample is taken from an artery then there are some chances of problems such as:
- There may be bruising at the puncture site. The risk of bruising can be decreased by applying pressure on the puncture site for at least 10 minutes after the needle is removed and longer if the patient is taking blood thinners or has bleeding problems.
- There may be a feeling of lightheadedness, dizziness or nausea while the blood is being collected from the artery.
- Patients with bleeding disorders and who are taking blood-thinning medicines, such as warfarin and aspirin, can have a risk of continuous bleeding. The doctor should be informed of all this before any blood sample is taken.
- In rare cases, there can be damage to the artery or the nerve from the needle, which can cause blockage in the artery.
Factors Which Affect the Ammonia Test
Some of the reasons where the patient cannot have the ammonia test done or where the results of the ammonia test are not helpful include:
- Taking medications which increase the level of ammonia in the blood, such as sodium valproate, acetazolamide and some diuretics.
- Consuming a low-protein or a high-protein diet.
- Taking medications, which decrease the level of ammonia in the blood, such as diphenhydramine, lactulose, isocarboxazid, , neomycin, tetracycline, phenelzine and tranylcypromine.
- Doing strenuous exercise just before the ammonia test.
Some Important Points about Ammonia Level
- The Ammonia Levels are not always an indication of the severity of the patient's symptoms. For example, an individual suffering from acute cirrhosis may only have slightly increased level of ammonia in the blood and yet may be sleepy or may not be thinking clearly or can be in a coma. On the other hand, individuals with very high levels of ammonia in the blood can think and act normally.
- Lactulose, which is a laxative, helps in treating the symptoms of an increased ammonia level, such as extreme sleepiness or confusion. Lactulose works by decreasing the production of ammonia in the intestines
- Slightly increased ammonia levels is common in newborns and they are temporary and often do not cause any symptoms.