This is a medical question of type : exams and tests 
 How to diagnose Alagille Syndrome ? 
 A health care provider diagnoses Alagille syndrome by performing a thorough physical exam and ordering one or more of the following tests and exams:
                
- blood test  - urinalysis  - x ray  - abdominal ultrasound  - cardiology exam  - slit-lamp exam  - liver biopsy  - genetic testing
                
Alagille syndrome can be difficult to diagnose because the signs and symptoms vary and the syndrome is so rare.
                
For a diagnosis of Alagille syndrome, three of the following symptoms typically should be present:
                
- liver symptoms, such as jaundice, pruritus, malabsorption, and xanthomas  - heart abnormalities or murmurs  - skeletal abnormalities  - posterior embryotoxon  - facial features typical of Alagille syndrome  - kidney disease  - blood vessel problems
                
A health care provider may perform a liver biopsy to diagnose Alagille syndrome; however, it is not necessary to make a diagnosis. A diagnosis can be made in a person who does not meet the clinical criteria of Alagille syndrome yet does have a gene mutation of JAG1. The health care provider may have a blood sample tested to look for the JAG1 gene mutation. The gene mutation can be identified in 94 percent of people with a diagnosis of Alagille syndrome.2
                
Blood test. A blood test involves drawing blood at a health care provider's office or a commercial facility and sending the sample to a lab for analysis. The blood test can show nutritional status and the presence of liver disease and kidney function.
                
Urinalysis. Urinalysis is the testing of a urine sample. The urine sample is collected in a special container in a health care provider's office or a commercial facility and can be tested in the same location or sent to a lab for analysis. Urinalysis can show many problems of the urinary tract and other body systems. The sample may be observed for color, cloudiness, or concentration; signs of drug use; chemical composition, including glucose; the presence of protein, blood cells, or bacteria; or other signs of disease.
                
X ray. An x ray is a picture created by using radiation and recorded on film or on a computer. The amount of radiation used is small. An x-ray technician performs the x ray at a hospital or an outpatient center, and a radiologista doctor who specializes in medical imaginginterprets the images. Anesthesia is not needed. The patient will lie on a table or stand during the x ray. The technician positions the x-ray machine over the spine area to look for "butterfly" vertebrae. The patient will hold his or her breath as the picture is taken so that the picture will not be blurry. The patient may be asked to change position for additional pictures.
                
Abdominal ultrasound. Ultrasound uses a device, called a transducer, that bounces safe, painless sound waves off organs to create an image of their structure. The transducer can be moved to different angles to make it possible to examine different organs. In abdominal ultrasound, the health care provider applies a gel to the patient's abdomen and moves a handheld transducer over the skin. The gel allows the transducer to glide easily, and it improves the transmission of the signals. A specially trained technician performs the procedure in a health care provider's office, an outpatient center, or a hospital, and a radiologist interprets the images; anesthesia is not needed. The images can show an enlarged liver or rule out other conditions.
                
Cardiology exam. A cardiologista doctor who treats people who have heart problemsperforms a cardiology exam in a health care provider's office, an outpatient center, or a hospital. During a full exam, a cardiologist may inspect the patient's physical appearance, measure pulse rate and blood pressure, observe the jugular vein, check for rapid or skipped heartbeats, listen for variations in heart sounds, and listen to the lungs.
                
Slit-lamp exam. An ophthalmologista doctor who diagnoses and treats all eye diseases and eye disordersperforms a slit-lamp exam to diagnose posterior embryotoxon. The ophthalmologist examines the eye with a slit lamp, a microscope combined with a high-intensity light that shines a thin beam on the eye. While sitting in a chair, the patient will rest his or her head on the slit lamp. A yellow dye may be used to examine the cornea and tear layer. The dye is applied as a drop, or the specialist may touch a strip of paper stained with the dye to the white of the patient's eye. The specialist will also use drops in the patient's eye to dilate the pupil.
                
Liver biopsy. A liver biopsy is a procedure that involves taking a piece of liver tissue for examination with a microscope for signs of damage or disease. The health care provider may ask the patient to stop taking certain medications temporarily before the liver biopsy. The patient may be asked to fast for 8 hours before the procedure.
                
During the procedure, the patient lies on a table, right hand resting above the head. A local anesthetic is applied to the area where the biopsy needle will be inserted. If needed, sedatives and pain medication are also given. The health care provider uses a needle to take a small piece of liver tissue. The health care provider may use ultrasound, computerized tomography scans, or other imaging techniques to guide the needle. After the biopsy, the patient should lie on the right side for up to 2 hours and is monitored an additional 2 to 4 hours before being sent home.
                
Genetic testing. The health care provider may refer a person suspected of having Alagille syndrome to a geneticista doctor who specializes in genetic disorders. For a genetic test, the geneticist takes a blood or saliva sample and analyzes the DNA for the JAG1 gene mutation. The geneticist tests for the JAG1 gene mutation first, since it is more common in Alagille syndrome than NOTCH2. Genetic testing is often done only by specialized labs. The results may not be available for several months because of the complexity of the testing.
                
The usefulness of genetic testing for Alagille syndrome is limited by two factors:
                
- Detection of a mutated gene cannot predict the onset of symptoms or how serious the disorder will be.  - Even if a mutated gene is found, no specific cure for the disorder exists.
                

                
When to Consider Genetic Counseling   People who are considering genetic testing may want to consult a genetics counselor. Genetic counseling can help family members understand how test results may affect them individually and as a family. Genetic counseling is provided by genetics professionalshealth care professionals with specialized degrees and experience in medical genetics and counseling. Genetics professionals include geneticists, genetics counselors, and genetics nurses.   Genetics professionals work as members of health care teams, providing information and support to individuals or families who have genetic disorders or a higher chance of having an inherited condition. Genetics professionals   - assess the likelihood of a genetic disorder by researching a family's history, evaluating medical records, and conducting a physical exam of the patient and other family members   - weigh the medical, social, and ethical decisions surrounding genetic testing   - provide support and information to help a person make a decision about testing   - interpret the results of genetic tests and medical data   - provide counseling or refer individuals and families to support services   - serve as patient advocates   - explain possible treatments or preventive measures   - discuss reproductive options    Genetic counseling may be useful when a family member is deciding whether to have genetic testing and again later when test results are available.