5.3 Quality Assurance, Quality Control & Preanalytical Risk Management

Quality Assurance, Quality Control & Preanalytical Risk Management

Delivering accurate laboratory test results requires systematic quality management across all diagnostic operations. In laboratory medicine, errors can cause misdiagnoses, delayed treatments, or inappropriate therapies. Phlebotomists play a vital role in quality management because test accuracy depends directly on specimen integrity.

Quality Assurance (QA) vs. Quality Control (QC)

• Quality Assurance (QA): An overall, institution-wide program that establishes policies, protocols, and continuous monitoring to ensure healthcare services consistently meet defined standards of excellence. QA encompasses patient preparation, turnaround time tracking, specimen transport conditions, customer satisfaction, and staff competency assessments.
• Quality Control (QC): Specific technical procedures used to verify that a specific laboratory instrument or assay performs within pre-established precision and accuracy limits. QC involves regularly testing control materials (samples containing known analyte target values) alongside patient specimens.

---

Total Testing Process & Preanalytical Risk Management

The Total Testing Process (TTP) describes the complete path of a diagnostic sample across three operational phases:

[1. PREANALYTICAL PHASE] -------> [2. ANALYTICAL PHASE] -------> [3. POSTANALYTICAL PHASE]
- Test ordering                   - Instrument calibration         - Result verification
- Patient ID & Fasting Prep       - Reagent mixing                 - Critical value calls
- Specimen draw & order of draw   - Sample analysis                - EMR result entry
- Centrifugation & transport      - QC evaluation                  - Specimen archiving

The Preanalytical Phase Risk

Extensive clinical research demonstrates that more than 70% of all diagnostic laboratory errors occur during the PREANALYTICAL phase. Because phlebotomists directly execute preanalytical tasks, strict adherence to standardized phlebotomy techniques is the single most effective defense against diagnostic errors.

Common Preanalytical Errors & Causes

---

Delta Checks & Patient Result Validation

A Delta check is an automated Laboratory Information System (LIS) algorithm that compares a patient's current test result with their most recent previous result for the exact same analyte.

If the difference (delta) exceeds pre-set limits, the LIS flags the result to alert staff to potential errors:

• Patient Misidentification: Sample collected from wrong patient.
• Contaminated Draw: Blood drawn above an active IV line.
• Additive Carryover: EDTA tube drawn prior to chemistry tube.
• Acute Clinical Change: Real physiological events (e.g., internal hemorrhage).

---

Levey-Jennings Charts & Westgard Multirule Evaluation

Daily QC values are plotted on Levey-Jennings (L-J) charts, which display the target mean flanked by standard deviation boundary lines (±1SD, ±2SD, ±3SD).

• Accuracy: Closeness of a measured value to its true target value.
• Precision: Reproducibility of repeated measurements.
• Trend: Gradual drift of QC values in one direction over 6+ runs (e.g., reagent aging).
• Shift: Abrupt change establishing a new mean on one side over 6+ runs (e.g., new calibrator lot).

Westgard Multirules

---

Equipment Maintenance Logs & Calibration

Equipment must be monitored and documented in daily maintenance logs:

• Blood Bank Refrigerators: Maintained strictly between 1°C and 6°C (with continuous alarms).
• Routine Refrigerators: Maintained between 2°C and 8°C.
• Freezers: Maintained at -20°C or lower (-80°C for ultralow freezers).
• Incubators: Maintained at 37°C ± 0.5°C.
• Centrifuge Speed Calibration: Centrifuge rotational speed (RPM) must be verified semi-annually (every 6 months) using a calibrated optical photo-tachometer.
• Centrifuge Balancing: Load tubes symmetrically (equal volume/weight directly opposite) to prevent breakage and severe vibration.

---

Clinical Scenario: EDTA Carryover Triggering Delta Check

A phlebotomist draws a Lavender (EDTA) tube before a Gold (SST) chemistry tube. The Gold tube shows a potassium result of 7.4 mEq/L (baseline 4.2 mEq/L) and a calcium result of 5.1 mg/dL (baseline 9.5 mg/dL). The LIS triggers a Delta check flag. Recognizing the classic EDTA carryover pattern (high K+, low Ca2+), the technician cancels the result and requests a redraw in correct Order of Draw, which yields normal values.

---

Common Exam Traps

Exam Trap 1: Over 70% of laboratory errors occur in the PREANALYTICAL phase.

Exam Trap 2: The 1-2s rule is a WARNING rule only; it does not require run rejection.

Exam Trap 3: Centrifuge speed is calibrated semi-annually using a photo-tachometer.

Exam Trap 4: Hemolysis falsely elevates serum Potassium (K+) due to intracellular release.