Standard Operating Procedure: Liver Function Test (LFT) Execution

This Standard Operating Procedure (SOP) outlines the standardized clinical protocol for performing a Liver Function Test (LFT), a diagnostic blood panel used to assess the health of the liver. The primary objective of this SOP is to ensure specimen integrity, minimize pre-analytical errors, and maintain strict patient safety standards throughout the phlebotomy and processing phases. Adherence to these guidelines is mandatory for all laboratory personnel to ensure accurate diagnostic reporting.

Phase 1: Patient Preparation and Verification

• Verify Identity: Confirm patient identity using at least two unique identifiers (e.g., full name and date of birth) against the laboratory requisition form.
• Fasting Confirmation: Ensure the patient has fasted for 8–12 hours, as per physician orders, as post-prandial lipemia can interfere with enzyme assays.
• Medication Review: Inquire about recent intake of hepatotoxic medications (e.g., acetaminophen, statins) or supplements that may influence bilirubin or enzyme levels.
• Informed Consent: Briefly explain the procedure to the patient and confirm they have no history of syncope during blood draws.

Phase 2: Specimen Collection

• Equipment Assembly: Gather the required materials: a serum separator tube (SST - gold or tiger top), 21G sterile needle, alcohol swab, tourniquet, gauze, and adhesive bandage.
• Site Selection: Identify a suitable vein in the antecubital fossa. Palpate for structural integrity; avoid sites with hematomas, edema, or intravenous lines.
• Aseptic Technique: Sanitize the site using a 70% isopropyl alcohol swab in a circular motion, moving outward. Allow the site to air-dry completely.
• Phlebotomy: Apply the tourniquet (no longer than 60 seconds). Perform venipuncture. Collect the required volume (typically 3–5 mL of blood).
• Tube Inversion: Gently invert the serum separator tube 5–8 times immediately after collection to ensure proper clot activator mixing. Do not shake.

Phase 3: Processing and Transport

• Labeling: Apply a unique patient barcode label to the tube immediately after collection while the patient is still present.
• Clotting Period: Allow the sample to stand vertically at room temperature for 30–60 minutes to achieve complete clot formation before centrifugation.
• Centrifugation: Process the specimen at 3000–3500 RPM for 10–15 minutes. Ensure the centrifuge is balanced.
• Inspection: Verify the absence of hemolysis, icterus, or lipemia in the serum. If the sample is heavily hemolyzed, reject it and request a recollection.
• Transport: Maintain a stable temperature environment. If transport is delayed, ensure the sample is refrigerated at 2–8°C.

Pro Tips & Pitfalls

• Pro Tip (Hemolysis Avoidance): Never draw blood through an existing IV line unless absolutely necessary, as this is the leading cause of false-positive potassium and AST results.
• Pro Tip (Tube Order): Always follow the standardized CLSI order of draw (SST tubes should be drawn after blood culture and coagulation tubes).
• Pitfall (Tourniquet Time): Prolonged tourniquet application causes hemoconcentration, which artificially elevates protein and enzyme levels, leading to skewed LFT results.
• Pitfall (Light Sensitivity): Bilirubin is photosensitive. Keep samples shielded from direct light once processed to prevent degradation.

Frequently Asked Questions (FAQ)

1. Why is an 8–12 hour fast required for LFTs? Fasting prevents spikes in triglycerides and metabolic byproducts that cause lipemia (cloudy serum). Lipemia interferes with spectrophotometric testing methods, leading to inaccurate readings for ALT, AST, and ALP.

2. What should I do if the serum appears reddish after centrifugation? This indicates hemolysis (ruptured red blood cells). You must reject the sample and perform a recollection, as the release of intracellular enzymes from RBCs will cause false elevations in AST and LDH levels.

3. Does hydration status affect LFT results? Yes. Significant dehydration can lead to hemoconcentration, which may result in artificially elevated albumin and liver enzyme levels. Always encourage the patient to stay hydrated with water prior to the fasting window.