Special Precautions

Accurate lipid testing relies on careful handling from start to finish. Pre-analytical steps are key to ensuring reliable results

Patient Preparation
- Fasting
- Medications
- Recent Illness/Surgery
- Posture
Specimen Collection
- Tube Type
- Order of Draw
- Tourniquet Time
Specimen Processing
- Timing
- Centrifugation
- Storage
Analytical Considerations
- Reagent Quality
- Calibration
- Quality Control (QC)
Interfering Substances
- Endogenous
- Exogenous

Patient Preparation

Fasting: Patients should typically fast for 9-12 hours before lipid testing
Rationale: Fasting is essential because triglyceride levels are significantly affected by recent food intake. Non-fasting samples can lead to falsely elevated triglyceride levels, affecting LDL cholesterol calculations
Medications: Certain medications can affect lipid levels
- Examples: Statins, fibrates, niacin, beta-blockers, oral contraceptives, corticosteroids
- Action: The healthcare provider should review the patient’s medication list and determine if any medications need to be temporarily discontinued before testing. Document all medications the patient is taking
Recent Illness/Surgery: Acute illness, surgery, or trauma can affect lipid levels
- Rationale: Stress and inflammation can temporarily alter lipid metabolism
- Action: Testing should be deferred until the patient has recovered from the acute event. Note any recent illnesses or surgeries on the test request form
Posture: The patient should be seated for at least 5 minutes before blood collection
- Rationale: Prolonged standing can affect plasma volume and lipid concentrations
- Action: Ensure the patient is comfortably seated before venipuncture

Tube Type: Serum separator tubes (SST) or plasma tubes with EDTA are commonly used
Rationale: SSTs allow for easy separation of serum, while EDTA tubes provide plasma samples. The choice depends on the laboratory’s standard operating procedures and the specific assays being performed
Action: Follow the laboratory’s guidelines for tube selection. Ensure the tubes are within their expiration date
Order of Draw: Follow the correct order of draw when collecting multiple tubes
- Rationale: To prevent cross-contamination from tube additives. Lipid panels are typically drawn after blood culture tubes and coagulation tubes
- Action: Follow CLSI guidelines for the order of draw
Tourniquet Time: Minimize tourniquet time (ideally less than 1 minute)
- Rationale: Prolonged tourniquet time can cause hemoconcentration, leading to falsely elevated lipid levels
- Action: Release the tourniquet as soon as blood flow is established, and before the last tube is filled

Timing: Process the specimen as soon as possible after collection
- Rationale: To prevent degradation of lipids and cellular metabolism affecting results
- Action: Centrifuge the sample within 1-2 hours of collection
Centrifugation: Centrifuge the sample according to the manufacturer’s instructions for the specific tube type
- Rationale: Proper centrifugation ensures complete separation of serum or plasma from cells
- Action: Use the correct speed and duration for centrifugation
Storage: If analysis is delayed, store the specimen refrigerated (2-8°C) for up to 7 days or frozen (-20°C or -70°C) for longer storage
- Rationale: To prevent lipid degradation
- Action: Aliquot the sample into smaller portions to avoid repeated freeze-thaw cycles, which can degrade lipids

Reagent Quality: Use high-quality reagents and store them according to the manufacturer’s instructions
- Rationale: To ensure accurate and reliable results
- Action: Check expiration dates and discard expired reagents
Calibration: Calibrate the instrument regularly using appropriate standards
- Rationale: To ensure accurate and precise measurements
- Action: Follow the manufacturer’s calibration schedule and procedures
Quality Control (QC): Run quality control samples at regular intervals to monitor the accuracy and precision of the assay
- Rationale: To detect any shifts or trends in the assay performance
- Action: Follow the laboratory’s QC procedures. Evaluate QC results before releasing patient results

Endogenous: Bilirubin, hemoglobin, lipemia
- Rationale: These substances can interfere with spectrophotometric assays, leading to inaccurate results
- Action: Use methods less susceptible to interference, or employ techniques to remove or correct for the interfering substance
Exogenous: Medications, contrast dyes
- Rationale: Certain medications and contrast dyes can affect lipid levels
- Action: Be aware of potential interferences from medications and contrast dyes. Document any such substances the patient has taken

High Lipid Results
- Pre-Analytical:
  - Patient not fasting
  - Prolonged tourniquet time
  - Improper collection tube
- Analytical:
  - Incorrect calibration
  - Reagent deterioration
  - Interfering substances
Low Lipid Results
- Pre-Analytical:
  - Improper storage
  - Lipid degradation
- Analytical:
  - Incorrect calibration
  - Reagent deterioration
Inconsistent Results
- Check patient preparation
- Review collection and processing procedures
- Evaluate reagent quality and calibration
- Consider interfering substances

Lipemia
- Interference: Causes turbidity, affecting spectrophotometric readings
- Mechanism: Lipids scatter light, leading to inaccurate absorbance measurements
- Mitigation:
  - Use lipemia clearing techniques (ultracentrifugation, lipid clearing reagents)
  - Consider methods less affected by turbidity
Bilirubin
- Interference: Absorbs light at similar wavelengths, affecting absorbance readings
- Mechanism: Competes with the chromogen for light absorption
- Mitigation:
  - Use methods less susceptible to bilirubin interference
  - Employ bilirubin correction techniques
Hemoglobin
- Interference: Absorbs light and can interfere with enzymatic reactions
- Mechanism: Released from hemolyzed red blood cells
- Mitigation:
  - Avoid hemolysis during collection and processing
  - Use methods less susceptible to hemoglobin interference
Ascorbic Acid (Vitamin C)
- Interference: Can interfere with certain enzymatic reactions
- Mechanism: Acts as a reducing agent
- Mitigation: Use methods less susceptible to ascorbic acid interference
Medications
- Interference: Certain drugs can directly affect lipid levels
- Examples:
  - Statins: Decrease cholesterol
  - Fibrates: Decrease triglycerides, increase HDL
  - Beta-blockers: Increase triglycerides, decrease HDL
  - Oral contraceptives: Increase triglycerides, decrease HDL
- Mitigation: Be aware of patient’s medication list

Pre-analytical: Processes that occur before the sample is analyzed
Analytical: Processes involved in analyzing the sample
Interfering Substance: A substance that affects the accuracy of a test
Lipemia: The presence of excess lipids in the blood
Hemolysis: The breakdown of red blood cells
Calibration: Adjusting an instrument to ensure accurate readings
Quality Control: Samples used to monitor the accuracy and precision of a test
Spectrophotometry: A method to measure the absorbance of light by a solution
Chromogen: A substance that produces a colored product
Enzymatic Method: A laboratory method that uses enzymes to catalyze a reaction
Immunochemical Methods: Laboratory methods that use antibodies to measure a substance