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Hematology

Preanalytical, Analytical, Postanalytical

Quality Assessment (QA), often used interchangeably with Quality Management (QM), encompasses the entire scope of the laboratory testing process. While Quality Control (QC) focuses specifically on the analytical phase (monitoring instrumentation and reagents), QA looks at the “Total Testing Process.” In Hematology, where cell fragility and morphology are time-sensitive, rigorous adherence to QA protocols is essential to prevent erroneous data that could lead to misdiagnosis or incorrect treatment. The process is divided into three distinct phases: Preanalytical, Analytical, and Postanalytical

Preanalytical

The preanalytical phase includes all steps taken prior to the specimen being analyzed by the instrument. Studies suggest that up to 70% of laboratory errors occur during this phase. In Hematology, specimen integrity is paramount because the analytes are whole cells that can degrade, lyse, or clump

Patient Preparation & Identification

  • Patient Identification: This is the single most critical step. Two unique identifiers (typically name and date of birth/medical record number) must be verified. Mislabeling constitutes a sentinel event
  • Physiologic Variables: Factors such as hydration status, altitude, and smoking can alter baseline hematology values. For example, dehydration causes spurious polycythemia (elevated RBC/Hct due to decreased plasma volume), while chronic smoking may elevate WBC and Hgb levels
  • Diurnal Variation: Certain cells, particularly eosinophils and cortisol-dependent leukocytes, show daily fluctuations. Standardization of collection times is preferred for serial monitoring

Specimen Collection

  • Order of Draw: To prevent cross-contamination of additives, Hematology (EDTA/Lavender) tubes are generally drawn after Serum and Citrate tubes but before Fluoride/Oxalate tubes
    • EDTA Contamination in Chemistry: Causes falsely low Calcium (chelation) and falsely high Potassium
    • K2 vs. K3 EDTA: K2 (spray-dried) is preferred as K3 (liquid) can cause RBC shrinkage, artificially lowering the Hematocrit and increasing MCHC
  • Venipuncture Technique: Prolonged tourniquet application (greater than 1 minute) causes hemoconcentration, elevating cellular indices. Traumatic venipuncture activates the coagulation cascade, leading to microclots that clog hematology analyzer apertures and falsely lower platelet counts
  • Capillary Collection: Skin punctures often contain interstitial fluid. Compared to venous blood, capillary blood usually has a slightly lower platelet count and higher hemoglobin/hematocrit

Specimen Handling & Transportation

  • Mixing: Immediate and gentle inversion (8–10 times) is required to mix the blood with the EDTA anticoagulant. Inadequate mixing leads to microclots; vigorous shaking causes hemolysis
  • Storage and Stability
    • CBC specimens are generally stable for 24 hours at room temperature, though WBC morphology begins to degrade causing “necrobiosis” (vacuolation, pyknosis)
    • Slides for manual differentials should be made within 2 to 3 hours of collection to avoid EDTA-induced artifacts (e.g., echinocytes, necrobiotic neutrophils)
    • Platelets are the most unstable parameter and can swell over time, potentially altering the MPV (Mean Platelet Volume)

Analytical

The analytical phase covers the actual testing of the specimen. This includes instrument maintenance, calibration, quality control (QC), and the identification and resolution of interfering substances

Internal Quality Control (IQC)

  • Commercial Controls: Laboratories run three levels of controls (Low, Normal, High) at least once every 24 hours (or per shift/run)
  • Levey-Jennings Charts: Data is plotted to visualize precision and accuracy
    • Shift: Abrupt change in the mean (e.g., new reagent lot, lamp replacement)
    • Trend: Gradual drift in data (e.g., deteriorating reagent, aging laser, dirty aperture)
  • Westgard Rules: Statistical rules used to accept or reject a run (e.g., 1-2s is a warning; 1-3s or 2-2s indicate rejection)
  • Moving Averages (Bull’s Algorithm): An automated QC method that averages RBC indices (MCV, MCH, MCHC) of consecutive patient samples (batches of 20). Because indices remain stable in a population, a drift in the moving average indicates instrument error rather than patient pathology

Common Hematology Interferences & Troubleshooting

A competent laboratory scientist must recognize when analyzer results “don’t add up.” This is primarily done by reviewing the Rule of Three (Hgb x 3 ≈ Hct ± 3) and the MCHC

Cold Agglutinins

  • Cause: IgM antibodies causing RBC agglutination at room temperature
  • Presentation: Visibly grainy blood on the side of the tube
  • Analyzer Data: Drastically elevated MCHC: (often >37 g/dL), decreased RBC count, falsely high MCV (clumps measured as single large cells)
  • Resolution: Warm the specimen to 37°C for 15–30 minutes and re-run immediately. If corrected, report warmed results and comment on the presence of cold agglutinins

Lipemia

  • Cause: High triglycerides or presence of lipids (TPN) in the plasma creates turbidity
  • Presentation: Plasma appears milky white
  • Analyzer Data: Elevated MCHC: and Elevated Hgb. The analyzer measures Hgb via spectrophotometry (turbidity = false high absorbance). The RBC count and Hematocrit are usually correct (measured by impedance/pulse detection)
  • Resolution: Saline replacement (plasma replacement) procedure. Spin down the specimen, remove lipemic plasma, replace with an equal volume of saline, mix, and re-run. Report the original RBC/Hct/Plt and the corrected Hgb/MCH/MCHC

Hemolysis (In Vitro)

  • Cause: Traumatic draw or rough handling
  • Analyzer Data: Decreased RBC count and Hct; MCHC may be elevated
  • Resolution: This creates a “Rule of Three” failure. Specimen must be rejected and redrawn

Lysis-Resistant RBCs

  • Cause: Hemoglobinopathies (Sickle Cell, Hb C) or severe liver disease make RBCs difficult to lyse in the WBC mixing chamber
  • Analyzer Data: Unlysed RBCs are counted as WBCs, leading to a falsely elevated WBC count
  • Resolution: Perform a manual WBC count or use a stronger lytic agent/extended lyse cycle if the instrument allows

Platelet Clumping (Pseudothrombocytopenia)

  • Cause: In vitro phenomenon where EDTA induces platelet clumping or platelet satellitism (platelets adhering to neutrophils)
  • Analyzer Data: Falsely decreased Platelet count: and Falsely increased WBC count (large clumps counted as lymphocytes). Reviewing the scatterplot/histogram will often show interference in the origin of the WBC or PLT curves
  • Resolution: Review the peripheral smear to confirm clumps. If clumps are present, redraw the patient using a Sodium Citrate (Light Blue) tube. Analyze the citrate tube and multiply the platelet result by 1.1: (to correct for the liquid anticoagulant dilution)

Nucleated RBCs (nRBCs) & Megakaryocyte Fragments

  • Problem: Most analyzers count cells based on size. nRBCs are roughly the size of lymphocytes
  • Analyzer Data: Falsely elevated WBC count
  • Resolution: Most modern analyzers automatically correct for nRBCs. If not, correct the WBC count using the manual differential count formula:
    • Corrected WBC = (Uncorrected WBC x 100) / (nRBCs + 100)

Postanalytical

The postanalytical phase involves the verification, reporting, and interpretation of the results after analysis. This phase ensures that the data released to the clinician is accurate and clinically actionable

Result Verification & Delta Checks

  • Delta Checks: The Laboratory Information System (LIS) compares the current result with the patient’s most recent previous result. Significant discrepancies (Deltas) flag the laboratory scientist to investigate
    • Example: An MCV jumping from 82 fL to 98 fL in 24 hours is physiologically impossible and likely indicates a mislabeled specimen or sample mix-up
  • Autoverification: Algorithms allow the LIS to automatically release results that fall within defined normal ranges and pass all instrument flag checks, allowing the laboratory scientist to focus on abnormal samples

Critical (Panic) Values

  • Critical values represent results that are life-threatening and require immediate intervention
  • Common Hematology Criticals
    • Hemoglobin < 7.0 g/dL (risk of hypoxia/heart failure)
    • Platelets < 10,000 - 20,000 /uL (risk of spontaneous hemorrhage)
    • INR > 5.0 (risk of bleeding)
    • Presence of Blasts on a differential (new diagnosis of Leukemia)
    • Presence of bacteria or malaria on a smear
  • Protocol: Confirm the result (repeat testing if necessary), call the appropriate caregiver, read back the information to verify accuracy, and document the call, time, and person notified in the LIS

Data Reporting & Archiving

  • Manual Differential Reporting: Ensure standard nomenclature is used. Comments regarding morphology (e.g., “Anisocytosis,” “Polychromasia,” “Dohle Bodies”) must be standardized and graded (1+, 2+, etc.) according to laboratory SOP
  • Correction Notations: When interfering substances are corrected (e.g., “Result corrected for Lipemia”), a comment must be appended to the final report so the physician understands the manipulation performed
  • Turnaround Time (TAT): Monitoring TAT is a postanalytical quality indicator. Delays in reporting critical hematology results can negatively impact patient safety