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Unit 1 of 3 · B.Sc MLS Sem 5

Unit 1: Quality assurance and automation

Applied Haematology-I notes · PTU syllabus (BMLS501-18)

3 min read5 topics9 exam questions
On this page
  1. Unit summary
  2. Quality control in haematology
  3. Statistical analysis
  4. Safety precautions
  5. Automated blood cell counters
  6. Coagulometers
  7. Key terms
  8. Quick revision
  9. Important questions

Unit summary

Haematology results are trusted only when quality is assured and analysers are understood. This unit covers internal and external quality control, routine QA protocols, statistical analysis — SD, CV, accuracy and precision — safety precautions, and automation in blood cell counters and coagulometers.

After this unit you can

  • Apply internal and external quality control in haematology
  • Calculate SD and CV and distinguish accuracy and precision
  • Follow safety precautions
  • Explain the principles of automated cell counters and coagulometers

PTU syllabus topics

  • Internal and external quality control
  • routine QA protocol
  • statistical analysis (SD, coefficient of variation, accuracy and precision)
  • safety precautions
  • basic concepts of automation — blood cell counters and coagulometers
Key formulasQC statistics

  • Mean

    x̄ = Σx / n

  • Standard deviation

    SD = √[Σ(x − x̄)² / (n − 1)]

  • Coefficient of variation

    CV% = (SD / mean) × 100

    Measures precision

  • Levey-Jennings rule

    Value beyond ±2 SD = warning; beyond ±3 SD = reject run

1

Topic 1

Quality control in haematology

ComparisonInternal and external QC
Internal QC
External QC (EQAS)

Purpose

Daily check of precision and run acceptance

Compare accuracy with other laboratories

Material

Commercial stabilised blood controls (low, normal, high); patient duplicates; moving averages (Bull's algorithm)

Survey samples from a provider (e.g., AIIMS, CMC Vellore EQAS)

Action

Westgard rules; reject run on violation

Investigate unsatisfactory scores (SDI above 2)

Key termsRoutine QA protocol
Pre-analytical
Correct tube, fill volume, mixing, labelling, time to analysis
Analytical
Daily startup, background checks, controls, calibration with calibrators
Post-analytical
Delta checks against previous results, smear review criteria, critical values
Documentation
QC charts, corrective actions, maintenance logs
2

Topic 2

Statistical analysis

Key formulasQC statistics

  • Mean

    Sum ÷ n

  • Standard deviation

    Square root of (sum of squared deviations ÷ (n − 1))

  • Coefficient of variation

    SD ÷ mean × 100

  • Standard deviation index

    (Lab mean − group mean) ÷ group SD

ComparisonAccuracy and precision
Accuracy
Precision

Meaning

Closeness to the true value

Closeness of repeated results to each other

Affected by

Systematic error (bias, calibration)

Random error

Checked by

EQAS, reference materials

Replicate testing, CV

Example

Ten Hb measurements of one sample: mean 12.0 g/dL, SD 0.12 → CV = 1.0% (good precision). If the true value is 13.0 g/dL, the method is precise but not accurate — recalibrate.

3

Topic 3

Safety precautions

  • Universal precautions; closed-tube sampling on analysers; disinfect probes and spills; safe disposal of lancets, slides and tubes; avoid aerosols when opening tubes; analyser waste is biohazardous.
4

Topic 4

Automated blood cell counters

ComparisonPrinciples of cell counting
Principle
Measures

Electrical impedance (Coulter principle)

Cells passing through an aperture interrupt current; pulse size ∝ cell volume

RBC, WBC, platelets; MCV; 3-part differential

Flow cytometry with laser light scatter

Forward scatter (size) and side scatter (granularity), sometimes fluorescence

5-part differential, reticulocytes, nucleated RBCs

Spectrophotometry

Hb converted (cyanide-free SLS method) and read

Haemoglobin

Calculated parameters

From measured values

HCT, MCH, MCHC, RDW

  • Flags: abnormal cells, platelet clumps, blasts — require peripheral smear review. Interferences: cold agglutinins (falsely high MCV, low RBC), lipaemia (high Hb), giant platelets.
5

Topic 5

Coagulometers

Key termsClot detection methods
Mechanical
Steel ball movement stops as the clot forms
Optical (photometric)
Change in light transmission as fibrin forms
Chromogenic
Colour release from a synthetic substrate — factor assays, anti-Xa
Immunological
Latex turbidimetry — D-dimer
  • QC: normal and abnormal control plasmas each shift; record reagent ISI for INR.

Key terms

Internal QC
Daily testing of control materials
Precision
Agreement among repeated measurements
Coulter principle
Counting and sizing cells by impedance
Delta check
Comparing a result with the patient's previous result
Coagulometer
Instrument detecting clot formation

Quick revision

  • Internal vs external QC; QA protocol phases; delta checks.
  • Mean, SD, CV, SDI; accuracy vs precision.
  • Safety on analysers.
  • Impedance, flow cytometry, spectrophotometric Hb; flags and interferences.
  • Mechanical, optical, chromogenic, immunological clot detection.

Important exam questions

Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).

Short-answer questions

  1. Q1.Distinguish accuracy and precision.
  2. Q2.Define coefficient of variation.
  3. Q3.What is a delta check?
  4. Q4.State the Coulter principle.
  5. Q5.Why are smears reviewed after analyser flags?
  6. Q6.Name two methods of clot detection.

Long-answer questions

  1. Q1.Describe quality assurance in haematology.
  2. Q2.Explain the principles of automated blood cell counters.
  3. Q3.Describe coagulometers and their quality control.

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