Overview
ALT catalyzes alanine–α-ketoglutarate amino transfer; serum activity rises with hepatocyte membrane injury.
Clinical Importance
Detect hepatocellular injury
Liver panel component and drug-monitoring pathways
Specimen Requirements
- Specimen: serum or lithium heparin plasma (method- and analyzer-dependent; follow the performing laboratory)
- Tube: gold/SST (serum separator) or green-top lithium heparin as validated locally
- Handling: invert gently; allow SST to clot fully before centrifugation; separate promptly
- Storage: refrigerate serum/plasma if testing is delayed per analyte stability limits
- Stability: analyte-specific; do not exceed institutional or manufacturer time/temperature limits
- Fasting: follow institutional/protocol fasting requirements when the ordered pathway requires fasting
Analytical Method
IFCC-aligned enzymatic rate methods measuring NADH consumption photometrically on chemistry analyzers.
Instruments Used
Automated analyzers
- Roche Cobas chemistry and immunoassay systems
- Abbott Alinity / Architect chemistry and immunoassay systems
- Siemens Healthineers Atellica / ADVIA chemistry and immunoassay systems
- Beckman Coulter AU / DxC chemistry systems
- Beckman Coulter Access / DxI immunoassay systems
- Mindray BS-series chemistry analyzers
- Ortho Clinical Diagnostics Vitros systems
- Thermo Fisher / Indiko and related chemistry platforms
- Randox clinical chemistry systems
Manual methods
- Manual spectrophotometric/immunoassay methods in selected reference or backup settings
Reference Values
Typical adult SI examples below follow widely published international clinical chemistry practice (e.g., Tietz; Henry's). Always interpret against the method- and demographics-specific interval printed on the patient report (CLSI EP28-A3c). Neonatal, pediatric, pregnancy, and assay-generation intervals differ.
Method-specific (IFCC vs older methods). Many adult upper limits approximate <35–55 U/L depending on sex and assay; use the report interval.
Interpretation
Common Causes of Increased Results
- Elevated ALT indicates hepatocellular injury pattern; magnitude and AST/ALT ratio aid laboratory pattern recognition
Common Causes of Decreased Results
- Low ALT is seldom clinically actionable
Clinical Significance
- Liver injury screening and monitoring
- Medication hepatotoxicity surveillance
Factors Affecting Results
Pre-analytical
- Hemolysis, lipemia, or icterus (analyte- and method-dependent interference)
- IV fluid contamination or draw above an infusion
- Prolonged tourniquet time; delayed separation of cells
- Wrong tube additive or incomplete clotting of SST
- Intramuscular injection or strenuous exercise may raise AST/CK-related enzymes
Analytical
- Calibration/QC failure; reagent lot shifts
- Carryover or substrate depletion on high-throughput analyzers
- Assay-specific interference (heterophile antibodies for immunoassays)
Post-analytical
- Wrong reference interval or unit applied
- Failure to review delta checks / critical values before release
Advantages and Limitations
Advantages
- Relatively liver-selective vs AST
- Automated and inexpensive
Limitations
- Not specific for a single liver disease
- May be normal in cirrhosis despite disease
Clinical Pearls
ALT is the hepatocellular workhorse; pair it with AST, ALP, GGT, and bilirubin for a pattern, not a diagnosis.
References
Authoritative textbooks, guidelines, and reviews supporting this laboratory test reference. Verify reference intervals, critical limits, and method details against institutional protocols and current guideline editions.
Textbooks
- Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 8th ed. Elsevier; 2022.
- McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2021.
- Bishop ML, Fody EP, Schoeff LE. Clinical Chemistry: Principles, Techniques, and Correlations. 9th ed. Jones & Bartlett; 2022.
CLSI and Professional Guidelines
- International Federation of Clinical Chemistry and Laboratory Medicine (IFCC). Recommendations and reference measurement systems for clinical chemistry measurands (verify current IFCC documents for the analyte).
- Clinical and Laboratory Standards Institute. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Standard. CLSI document EP28-A3c. CLSI; 2010.
- Clinical and Laboratory Standards Institute. Collection of Diagnostic Venous Blood Specimens. CLSI standard GP41. CLSI.
- American Diabetes Association. Standards of Care in Diabetes. Diabetes Care (annual update).
- Kidney Disease: Improving Global Outcomes (KDIGO). Clinical Practice Guideline for Evaluation and Management of Chronic Kidney Disease.
- American Association for the Study of Liver Diseases (AASLD). Practice guidance related to evaluation of abnormal liver chemistries / liver disease laboratory evaluation (verify current AASLD publication and institutional adoption).
Frequently Asked Questions
Common questions about using this Alanine Aminotransferase (ALT) laboratory test Medical Laboratory Library reference in Medical Laboratory Science education.
What is the Alanine Aminotransferase (ALT) laboratory test reference used for?
This Medical Laboratory Library page summarizes the clinical importance of Alanine Aminotransferase (ALT). Review the Clinical Importance section for why the test is ordered in laboratory medicine practice.
Where can I find Alanine Aminotransferase (ALT) specimen requirements?
See the Specimen Requirements section on this page for specimen information related to Alanine Aminotransferase (ALT). Confirm collection details against your laboratory protocol.
Where are Alanine Aminotransferase (ALT) reference values listed?
See the Reference Values section on this Laboratory Library page. Reference ranges can vary by method and population, so verify intervals with your laboratory.
How do I interpret Alanine Aminotransferase (ALT) results?
Use the Interpretation section for laboratory interpretation framing, including increased and decreased result patterns when provided. Do not treat educational text as a patient-specific diagnosis.
What analytical method is used for Alanine Aminotransferase (ALT)?
See the Analytical Method section for principle and method notes. Method details may differ by instrument and institutional SOP.
Are related laboratory tests linked from Alanine Aminotransferase (ALT)?
Yes. The Related Laboratory Tests section lists connected references for continued lookup in the Medical Laboratory Library.
How can I continue learning after reading Alanine Aminotransferase (ALT)?
Use Continue learning links on this page for related Academy lessons, medical laboratory quizzes, or laboratory case studies when available for this Clinical Chemistry topic.
What are the clinical pearls for Alanine Aminotransferase (ALT)?
See the Clinical Pearls section for concise laboratory practice notes associated with Alanine Aminotransferase (ALT). Apply pearls alongside institutional protocols.
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