The Alanine Aminotransferase (ALT) Test Kit is a clinical chemistry reagent system designed for the quantitative determination of ALT (formerly SGPT) catalytic activity in human serum and plasma. Built on the IFCC-recommended UV kinetic method, the kit delivers rapid, precise, and reproducible liver function assessment on both automated biochemistry analyzers and manual spectrophotometers. This article presents a complete technical overview of the kit, including its reaction principle, sample requirements, testing methodology, performance specifications, and applications in clinical diagnostics and research.
Technical Overview
Alanine aminotransferase (ALT, EC 2.6.1.2), historically known as serum glutamate pyruvate transaminase (SGPT), is a pyridoxal phosphate-dependent enzyme found predominantly in the cytoplasm of hepatocytes. Because ALT is concentrated primarily in the liver, elevated serum ALT activity is widely regarded as one of the most specific biochemical markers of hepatocellular injury. The Alanine Aminotransferase Test Kit provides a liquid-stable, ready-to-use two-reagent system optimized for the IFCC-recommended coupled-enzyme kinetic assay.
The assay is based on a two-step enzymatic reaction. In the first step, ALT catalyzes the transfer of an amino group from L-alanine to alpha-ketoglutarate, producing pyruvate and L-glutamate. In the second step, lactate dehydrogenase (LDH) converts pyruvate to lactate while oxidizing NADH to NAD+. The rate of NADH consumption, monitored as a decrease in absorbance at 340 nm, is directly proportional to ALT catalytic activity in the sample.
- Method: IFCC-recommended UV kinetic method (without pyridoxal phosphate supplementation)
- Reaction direction: Decreasing absorbance (negative kinetic reaction)
- Primary wavelength: 340 nm (secondary: 405 nm or 700 nm; 334 nm and 365 nm also acceptable)
- Reaction temperature: 37 degrees C
- Typical reagent ratio: R1 1000 uL + sample 100 uL + R2 250 uL (adjustable per analyzer programming)
- Linearity: Up to 600 U/L (or higher, depending on instrument configuration)
- On-board stability: Approximately 30 days at 2-8 degrees C on capped analyzer positions
- Shelf life: 12-18 months from manufacture when stored at 2-8 degrees C and protected from light
Testing Samples
Serum
Serum is the preferred sample type for ALT determination. Venous blood should be collected into a plain tube or separator tube and allowed to clot completely before centrifugation. Fasting samples are not strictly required, but patients should avoid alcohol consumption and strenuous exercise prior to collection, as both can transiently elevate ALT activity.
Plasma
Heparinized and EDTA anticoagulated plasma are acceptable alternatives to serum. Citrate plasma should be avoided unless validated, as citrate may interfere with enzyme kinetics. Plasma samples should be separated from cells promptly after collection to prevent leakage of enzymes from cellular components.
Sample Storage and Handling
- Stable for up to 24-72 hours at 2-8 degrees C
- Stable for several weeks at -20 degrees C; avoid repeated freeze-thaw cycles
- Grossly hemolyzed samples should be rejected, since erythrocytes release intracellular enzymes and adenosine derivatives that interfere with the NADH-dependent reaction
- Severely lipemic or icteric samples may require ultracentrifugation or blank correction
Testing Items
The kit quantitatively measures ALT catalytic activity concentration, reported in units per liter (U/L), where one unit is defined as the amount of enzyme that converts one micromole of substrate per minute under the specified reaction conditions. ALT testing is routinely performed as part of a comprehensive liver function panel alongside AST, ALP, GGT, total bilirubin, and albumin.
- Typical adult reference intervals (37 degrees C, to be verified by each laboratory): Men up to approximately 41 U/L; women up to approximately 33 U/L
- Results exceeding the linear range should be diluted with isotonic saline and re-assayed, multiplying the result by the dilution factor
- Each analytical run should include a two-level quality control material, and calibration should be performed using a traceable enzymatic calibrator
Testing Methods
UV Kinetic (Rate) Assay Principle
The assay employs the coupled LDH-NADH indicator reaction recommended by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC). Because NADH exhibits strong absorbance at 340 nm while NAD+ does not, the linear decline in absorbance provides a continuous, real-time readout of enzymatic rate.
Assay Procedure
- Step 1: Dispense R1 (buffer containing L-alanine, NADH, LDH, and preservatives) into the reaction cuvette
- Step 2: Add the sample, mix, and incubate at 37 degrees C for approximately 5 minutes to consume endogenous pyruvate and minimize blank interference
- Step 3: Add R2 (alpha-ketoglutarate solution) to initiate the ALT-catalyzed reaction
- Step 4: After a lag phase of approximately 60 seconds, monitor the decrease in absorbance at 340 nm for 1-3 minutes and record the change in absorbance per minute
Calculation
ALT activity is calculated from the measured absorbance change using the following formula: ALT (U/L) = (Delta A per minute x total reaction volume in uL x factor) divided by (molar absorptivity of NADH at 340 nm x path length x sample volume in uL), where the molar absorptivity of NADH is 6.3 L per mmol per cm. Most automated analyzers apply a pre-programmed factor automatically.
Applications
- Clinical diagnostics: Screening and monitoring of acute and chronic hepatitis, alcoholic and non-alcoholic fatty liver disease, cirrhosis, and autoimmune liver disorders
- Drug safety monitoring: Detection of drug-induced liver injury (DILI) in patients undergoing hepatotoxic therapies such as tuberculosis treatment, chemotherapy, or statin therapy
- Blood bank screening: Evaluation of donor liver enzyme status as part of transfusion safety workflows
- Pharmaceutical and toxicological research: In vitro and in vivo hepatotoxicity assessment during preclinical drug development
- Veterinary medicine: Liver function evaluation in companion animals and livestock using validated species-specific reference intervals
- Occupational and public health surveillance: Population-level liver health screening in occupational exposure programs
FAQ
What does an elevated ALT result mean?
Elevated serum ALT indicates hepatocellular damage but does not identify a specific cause. Common etiologies include viral hepatitis, fatty liver disease, alcohol abuse, medication or herbal supplement toxicity, and cirrhosis. Mild elevations may also occur after intense physical exercise or due to skeletal muscle injury. Clinical interpretation should always combine ALT with AST, ALP, GGT, bilirubin, and patient history.
What is the difference between ALT and AST?
ALT is found mainly in the liver and is therefore more liver-specific, whereas AST is present in heart, skeletal muscle, kidney, and liver tissue. The AST-to-ALT ratio (De Ritis ratio) can help differentiate alcoholic liver disease, viral hepatitis, and extrahepatic causes of enzyme elevation.
Can the kit be used on automated chemistry analyzers?
Yes. The kit is supplied as a liquid-stable, ready-to-use formulation compatible with most open-system automated biochemistry analyzers, including major open platforms from leading manufacturers. Instrument-specific application parameters are provided in the package insert.
Why are hemolyzed samples unsuitable?
Hemolysis releases intracellular enzymes and reducing substances from erythrocytes into the serum or plasma, causing falsely low or erratic results in NADH-dependent kinetic assays. Hemolyzed specimens should be recollected whenever possible.
How should results above the linear range be handled?
Samples exceeding the declared linear limit should be diluted with isotonic saline, re-assayed, and the measured value multiplied by the dilution factor. Results should be flagged for clinical review accordingly.
What quality control practices are recommended?
Laboratories should run at least two levels of quality control material with each analytical batch or per local regulatory requirements, apply standard statistical quality control rules such as Westgard rules, recalibrate when control results fall outside acceptance limits, and participate in external quality assessment programs to ensure long-term result comparability.