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Hematology

Quality Assessment & Troubleshooting

Quality Assessment (QA) in Hematology is a total management process designed to guarantee the accuracy and reliability of test results. While Quality Control (QC) is a specific component focusing on instrumentation, QA encompasses the entire workflow - from the moment a physician orders a test to the final interpretation of the result. For the laboratory scientist, mastery of these concepts is required not only for regulatory compliance but for patient safety, as Hematology involves time-sensitive cellular analysis prone to specific artifacts

Total Testing Process

The testing workflow is segmented into three phases. Errors can occur in any phase, though preanalytical errors are the most frequent

Preanalytical Phase (Specimen Integrity)

This phase covers all steps before the sample is analyzed. In Hematology, the physical state of the cell is the analyte; therefore, collection technique and additive choice are critical

  • Specimen Collection: The Lavender top (EDTA) is the standard. K2 EDTA (spray-dried) is preferred over K3 EDTA (liquid) to prevent RBC shrinkage. Hematology tubes must be drawn after serum tubes to avoid additive carryover (e.g., EDTA carryover into chemistry tubes causes falsely low calcium and high potassium)
  • Common Artifacts
    • Microclots: Caused by inadequate mixing or traumatic venipuncture. These clog instrument apertures and lower platelet counts
    • Hemolysis: Caused by vigorous shaking or small needle gauge. This decreases RBC count and Hematocrit, violating the “Rule of Three.”
    • Old Specimens: Samples >24 hours old show “necrobiosis” in WBCs and swelling of platelets, which may affect the Mean Platelet Volume (MPV)

Analytical Phase (Testing & Troubleshooting)

This phase involves the actual measurement procedure. The laboratory scientist must recognize interferences that cause data mismatch. A primary tool for verification is the Rule of Three, where Hgb x 3 ≈ Hct (±3)

  • Cold Agglutinins: IgM antibodies cause RBCs to clump at room temperature
    • Data: Falsely low RBC, falsely high MCV, and drastically elevated MCHC: (>37 g/dL)
    • Fix: Warm specimen to 37°C and re-run
  • Lipemia: High triglycerides increase turbidity, affecting the spectrophotometric reading of Hemoglobin
    • Data: Elevated Hgb and Elevated MCHC; RBC and Hct are usually normal
    • Fix: Perform a Saline Replacement (replace plasma with saline) to correct Hgb
  • Platelet Clumping (Pseudothrombocytopenia): EDTA-induced clumping
    • Data: Falsely low Platelets, falsely high WBCs (clumps counted as lymphocytes)
    • Fix: Redraw in Sodium Citrate (Light Blue), run, and multiply platelet result by 1.1

Postanalytical Phase (Reporting)

This phase ensures results are plausible and actionable before release

  • Delta Checks: The Laboratory Information System (LIS) compares current results to previous patient history. Improbable changes (e.g., MCV shifting from 80 fL to 100 fL overnight) trigger an investigation into mislabeling
  • Critical Values: Life-threatening results (e.g., Hgb < 7.0 g/dL, Plt < 20,000/µL, presence of Blasts) require immediate communication to the provider, with read-back verification and documentation

Quality Control (QC)

QC monitors the precision and accuracy of the analytical phase. It typically involves running commercial control materials (Low, Normal, High) and analyzing the data statistically

  • Statistical Parameters
    • Mean: The target value (measures Accuracy)
    • Standard Deviation (SD): The measure of dispersion (measures Precision)
    • Levey-Jennings Charts: Visual graphs used to plot daily control values to identify errors
  • Types of Error
    • Random Error: Unpredictable scatter (e.g., bubble in line, voltage spike). Identified by 1-3s or R-4s rules
    • Systematic Error: A shift or trend indicating a loss of accuracy (e.g., aging reagents, protein buildup, calibration loss). Identified by 2-2s, 4-1s, or 10x rules
  • Moving Averages (Bull’s Algorithm / X-B): A unique hematology QC method that averages the RBC indices (MCV, MCH, MCHC) of batches of 20 patient samples. Because indices are stable in a population, a drift in the X-B indicates instrument drift

Point-of-Care Testing (POCT)

POCT brings the laboratory to the bedside (e.g., HemoCue, i-STAT). While it improves turnaround time, it carries high risk because operators are often non-laboratory personnel

  • Methodologies
    • HemoCue: Uses a microcuvette to convert hemoglobin to azidemethemoglobin (photometric). Air bubbles in the cuvette are a major source of error
    • Handheld Analyzers (i-STAT): Often calculate Hgb/Hct via conductivity. Results can be skewed by abnormal plasma protein levels
  • Quality Management
    • QC Lockout: A critical feature where the device disables patient testing if Liquid QC fails or is not run on schedule
    • Confirmatory Testing: Critical or questionable POCT results must always be confirmed by a venous draw sent to the central laboratory

Regulation & Compliance

The laboratory operates under the Clinical Laboratory Improvement Amendments (CLIA ’88), often inspected by agencies like CAP or TJC

  • Proficiency Testing (PT)
    • External agencies send “blind” samples to the lab
    • Must be tested exactly like patient samples: by routine staff
    • Inter-laboratory communication regarding PT samples is strictly prohibited (collusion) and can result in license revocation
  • Competency Assessment
    • Verifies staff skill retention (distinct from training)
    • Must occur Semiannually (first year) and Annually thereafter
    • Must include Six Elements: Direct observation of test, Direct observation of maintenance, Review of records, Review of QC/PT, Problem-solving skills, and Specimen handling
  • Method Validation
    • Before a new instrument goes live, the lab must verify Accuracy, Precision, Reportable Range (Linearity), and Reference Intervals