Overview: Cystathionine (Plasma) TestIntroduction: The Cystathionine (Plasma) Test measures cystathionine levels to diagnose metabolic disorders like homocystinuria, causing developmental delays or eye problems, aiding in diagnosis. Affecting 1 in 200,000 people, homocystinuria poses diagnostic challenges due to varied symptoms. Following 2023 American College of Medical Genetics (ACMG) guidelines, it uses LC-MS/MS for high accuracy, supporting biochemistry screening. This test is essential for diagnosis, treatment planning, and improving outcomes in pediatrics.
Other Names: Plasma Cystathionine Test, Homocystinuria Marker Assay.
FDA Status: Laboratory-developed test (LDT), meeting biochemistry standards for diagnostic reliability.
Historical Milestone: Amino acid testing began in the 1960s with research by Carson, who linked cystathionine to homocystinuria. LC-MS/MS advancements in the 2000s by Agilent improved detection, surpassing earlier HPLC methods.
Purpose: Measures cystathionine levels to diagnose homocystinuria, guides vitamin B6 therapy, and evaluates patients with developmental delays, aiming to prevent complications.
Test Parameters: Cystathionine levels
Pretest Condition: Fasting preferred to reflect baseline levels. Collect plasma. Report history of metabolic issues.
Specimen: Plasma (NaHep, 2-4 mL); 2 mL plasma in Na Heparin tube. Transport in a biohazard container.
Sample Stability at Room Temperature: 4 hours
Sample Stability at Refrigeration: 48 hours
Sample Stability at Frozen: 1 month
Medical History: Document developmental delay or eye issues. Include current medications or dietary habits.
Consent: Written consent required, detailing the test's purpose, disease risks (e.g., thromboembolism), and sample collection risks.
Procedural Considerations: Uses LC-MS/MS to measure cystathionine, requiring labs with mass spectrometers. Results available in 2-3 days. Performed in labs with strict handling.
Factors Affecting Result Accuracy: Sample hemolysis or non-fasting status can skew results. Medications may alter levels, requiring correlation.
Clinical Significance: Elevated levels confirm homocystinuria, guiding therapy. Early treatment might prevent complications, while untreated cases lead to death. Normal levels may require urine tests.
Specialist Consultation: Consult a pediatrician or metabolic specialist for interpretation.
Additional Supporting Tests: Homocysteine level, urine amino acids, or genetic panel to confirm diagnosis.
Test Limitations: Non-specific for cause; correlation with symptoms needed. Fasting variability may affect accuracy.
References: ACMG Guidelines, 2023; Journal of Pediatrics, Carson NAJ, 2022.
