Standard Operating Procedure: Liver Function Test (LFT) Execution

Introduction

The Liver Function Test (LFT) is a diagnostic panel used to screen for, detect, or monitor liver disease or damage. This SOP outlines the professional standard for the pre-analytical, analytical, and post-analytical phases of the LFT process. Adherence to these protocols ensures clinical accuracy, patient safety, and sample integrity. All laboratory personnel must follow these steps to minimize pre-analytical errors such as hemolysis or incorrect patient preparation, which can lead to misleading bilirubin, enzyme, or protein levels.

Step-by-Step Checklist

1. Patient Preparation and Verification

• Confirm the patient's identity using two unique identifiers (full name and DOB/ID number).
• Verify the test requisition form for LFT order accuracy.
• Confirm patient fasting status (ideally 8–12 hours, depending on laboratory policy).
• Inquire about recent intake of medications (e.g., statins, antibiotics) or alcohol, as these can affect ALT/AST levels.
• Explain the procedure clearly to the patient to ensure informed cooperation.

2. Specimen Collection and Handling

• Sanitize hands and don appropriate Personal Protective Equipment (PPE).
• Perform venipuncture using a standard 21G needle and vacutainer system.
• Use a Serum Separator Tube (SST/Gold Top) or Serum (Red Top) tube.
• Ensure proper labeling of the tube immediately after collection at the patient’s bedside.
• Gently invert the tube 5–8 times to initiate clotting; do not shake.
• Allow the sample to clot vertically for at least 30 minutes at room temperature before centrifugation.

3. Sample Processing and Analysis

• Centrifuge the sample at 3,000–3,500 RPM for 10 minutes to ensure clear serum separation.
• Inspect the serum for hemolysis, icterus, or lipemia, as these conditions interfere with spectrophotometric analysis.
• Load the sample into the automated clinical chemistry analyzer.
• Perform daily Quality Control (QC) runs (Level 1 and Level 2) prior to patient sample analysis.
• Validate that all QC results fall within the ±2 SD (Standard Deviation) range established by the laboratory.

4. Result Validation and Reporting

• Review automated results for flagging errors (e.g., "Critical Value" or "Result Exceeds Linearity").
• Ensure the correlation between clinical history and test results (e.g., significant elevation in ALT vs. GGT).
• Transmit verified results to the Laboratory Information System (LIS).
• Flag critical results (e.g., extremely high bilirubin or transaminases) to the attending physician immediately via established emergency communication protocols.

Pro Tips & Pitfalls

• The Hemolysis Trap: Hemolysis is the #1 cause of false elevations in AST and LDH. If the sample is pink/red-tinged, reject it and request a recollection.
• Light Sensitivity: Bilirubin is highly photosensitive. Always store samples away from direct fluorescent or sunlight to prevent artificial degradation.
• Centrifugation Timing: Do not centrifuge before the sample has fully clotted. Insufficient clotting leads to fibrin strands that clog automated analyzer probes.
• Fasting: Remind patients that "fasting" includes avoiding alcohol for 24 hours, as alcohol can acutely influence liver enzymes.

Frequently Asked Questions (FAQ)

Q: Why is patient fasting required for an LFT? A: While many LFT components are stable, fasting is required to obtain accurate baseline levels of GGT and to prevent lipemia, which can interfere with the optical readings of the analyzer.

Q: What should I do if the patient is on medications that affect liver enzymes? A: You should record the medication name on the laboratory request form. This allows the pathologist or physician to interpret "elevated" results in the context of drug-induced liver injury rather than primary disease.

Q: Can I use a plasma (EDTA) tube for LFTs? A: No. Serum (clotted) is the gold standard for LFT panels. EDTA can chelate metal ions and interfere with enzyme assays, leading to inaccurate results for tests like Alkaline Phosphatase (ALP).