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ANALYTICAL PROCESS CONTROL QC for QUALITATIVE TESTS John Elliot WHO Collaborating Centre PPTC, Wellington, NZ Laboratory Sections that use Qualitative Tests • Microbiology • Blood Transfusion • Infectious Diseases Serology PPTC, Wellington, NZ INTERNAL QUALITY CONTROL (IQC) IQC REFERS TO THE SET OF PROCEDURES UNDERTAKEN BY THE LABORATORY STAFF FOR THE CONTINUOUS AND IMMEDIATE MONITORING OF LABORATORY WORK IN ORDER TO DECIDE WHETHER THE RESULTS ARE RELIABLE ENOUGH TO BE RELEASED. PPTC, Wellington, NZ What is IQC? • The regular testing of quality control [QC] material along with the patient samples • Comparison of the QC results to specific statistical limits [ranges] • Rejection of patient results if QC is outside of limits But does this apply to qualitative tests? If not, Why not? PPTC, Wellington, NZ WHAT IS THE MOST COMMON LABORATORY ERROR? TRANSCRIPTION Not technical PPTC, Wellington, NZ Microbiology Quality Control Accuracy and clinical value of results depend on: • Quality of specimen • Validity of test method • Performance of test procedure, reagents and media • Reports and interpretation • Staff • Equipment PPTC, Wellington, NZ In Microbiology how do we QC • The Quality of the specimen • The Performance of test procedures, reagents and media PPTC, Wellington, NZ 1. Specimen • Appropriate specimen • Collection method • Delivery system PPTC, Wellington, NZ Gram Stain PPTC, Wellington, NZ PPTC, Wellington, NZ PPTC, Wellington, NZ IDENTIFICATION SYSTEM PPTC, Wellington, NZ 2. Specimen Processing: Test Methods • • • • • Staining and Microscopy Culture Media Incubation Organism Identification Antimicrobial Susceptibility Testing PPTC, Wellington, NZ Culture Media: Both Solid and Liquid • • • • • • • • Dating when received and when opened Weighing Dissolving Sterilizing Storage of prepared media Addition of enrichments [eg Blood] Sterility Testing Incubation of inoculated media PPTC, Wellington, NZ QC of Media • Agar Plates » Haemolysis controls » Selective media controls • Liquid broths » Positive and negative reactions – Therefore Stock Cultures PPTC, Wellington, NZ Stock QC organisms • Organisms to be maintained must be adequate to check all media and test systems. – E. coli – MacConkey, XLD, susceptibility tests – Staphylococcus aureus – Blood agar, Mannitol Salt, susceptibility tests – Neisseria gonorrhoeae – chocolate, Thayer-Martin PPTC, Wellington, NZ QC of Stains and Reagents • Gram stain QC – Use gram positive and gram negative organisms to check regularly [at least once a week] • ZN QC – Use positive and negative AFB slide with every batch stained. • Other Stains – Check as used – positive and negative reactions • Reagents – Check as used with known positives and negatives. PPTC, Wellington, NZ Temperature Chart:Incubator PPTC, Wellington, NZ Temperature Chart: Refrigerator PPTC, Wellington, NZ Antimicrobial Susceptibility Testing • Storage of antibiotic disks • Correct concentration of antibiotic in disk • Joan Stokes Method • NCCLS Method – Detailed QC Procedures to ensure reproducability of results – Depth of agar!! PPTC, Wellington, NZ Antimicrobial Susceptibility Testing PPTC, Wellington, NZ Detecting Errors • Many organisms have predictable antimicrobial test results – Staphylococcus spp. are usually susceptible to vancomycin – Streptococcus pyogenes are always susceptible to penicillin – Klebsiella pneumoniae are resistant to ampicillin PPTC, Wellington, NZ Sources of Error • If you encounter an unusual pattern – rule out error by checking identification of organisms – repeat antimicrobial susceptibility test • Report if repeat testing yields same result, or refer the isolate to a reference laboratory for confirmation PPTC, Wellington, NZ QC in Blood Transfusion Service PPTC, Wellington, NZ Blood Transfusion Service Blood Bank Recipients Donors Safety Precautions Recruit – Screen – Bleed test – process – Xmatch transfuse – follow up PPTC, Wellington, NZ QC in Blood Bank Technology • • • • Donor services Blood grouping Crossmatch & antibody screening Transfusion PPTC, Wellington, NZ QC in Blood Bank • Positive and negative controls on all tests • Reverse grouping • Good documentation, SOPs etc • Equipment monitoring, calibration, maintenance PPTC, Wellington, NZ QC of Rapid Tests for Infectious Diseases PPTC, Wellington, NZ Infectious Diseases Serology QC of Rapid Methods • IQC • Positive controls • Negative controls » How often? » Where do you get the controls from? PPTC, Wellington, NZ PPTC, Wellington, NZ Qualitative vs.Quantitative • Quantitative test – measures the amount of a substance present • Qualitative test – determines whether the substance being tested for is present or absent PPTC, Wellington, NZ What is Quality Control? • Process or system for monitoring the quality of laboratory testing, and the accuracy and precision of results • Routinely collect and analyze data from every test run or procedure • Allows for immediate corrective action PPTC, Wellington, NZ Designing a QC Program – • Establish written policies and procedures – Corrective action procedures • Train all staff • Design forms • Assure complete documentation and review PPTC, Wellington, NZ