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Diagnostic Services

Genetics Lab


Tyrosinemia Type I - Orfadin Quantitation

Tyrosinemia type I is an autosomal recessive disorder caused by a deficiency of the enzyme fumarylacetoacetate hydrolase (FAH). The disease manifests primarily as liver disease, with hepatic cirrhosis and accompanying renal tubule damage as a result of the build up of succinylacetone. Biochemically, the hallmarks of the disease are elevated blood tyrosine and methionine, elevated blood alpha-fetoprotein, and succinylacetone in the urine. The diagnosis is confirmed by the presence of succinylacetone in urine. Tyrosinemia type I is treated by a low-tyrosine diet and the medication Orfadin (nitisinone). Nitisinone blocks the tyrosine breakdown pathway prior to the FAH deficiency and prevents the formation of succinylacetone.

Test Name: NTBC (Orfadin) Level
Test Code:
Test Description:
Quantitative assay of blood nitisinone levels.
NTBC, Orfadin, Nitisinone, Tyrosinemia type I monitoring
For monitoring therapeutic drug levels in patients being treated with Orfadin (nitisinone).
Related Tests: Tyrosinemia Type I (6 mutations)  
This test is used to provide additional information regarding diagnosed patients, provide carrier testing for at-risk family members or general population carrier testing.

Succinylacetone Screening, Urine  
This is a semi-quantitative assay for succinylacetone as part of urine organic acids. This screen is used for patients suspected of having tyrosinemia type I.

Succinylacetone Quantitation, Urine  
This stable isotope assay is used for monitoring known patients with tyrosinemia type I

Clinical Links: Tyrosinemia Type I GeneReview
University of Washington Tyrosinemia Webpage
Collected daily
Turnaround Time:
7 days
Electrospray Tandem Mass Spectrometry
Reference Range:
Treatment should lead to normalized porphyrin metabolism; a general target for blood levels is 50-60 mcmol/L. Succinylacetone should not be detectable in urine or plasma. It may take up to three months before the level of plasma succinylacetone is normalized after the start of nitisinone treatment.
Consent Form:
Sample Requirements: Type
Whole blood: 1ml green (heparin) tube

Spin, freeze plasma (need 0.5ml plasma)

Ship frozen overnight.
Samples Received:
Mon - Fri 8:00am - 5:00pm PST
Special Considerations:
Therapeutic reference range was established in patients with tyrosinemia type I and may not apply to patients with other disorders who are taking nitisinone
Please e-mail Client Services or call at 206-987-2617 with any billing questions
CPT Code:
Please e-mail Client Services or call at 206-987-2617 with any billing questions