Errors related to clinical laboratory
- 3. ERROR • AN ERROR IS THE DIFFERENCE BETWEEN THE TRUE RESULT AND THE MEASURED RESULT. • IF THE ERROR IN AN ANALYSIS IS LARGE, SERIOUS CONSEQUENCES MAY RESULT. • A PATIENT MAY UNDERGO SERIOUS MEDICAL TREATMENT BASED ON AN INCORRECT LABORATORY RESULTS.
- 4. IN OTHER WORDS • LABORATORY ERRORS ARE DESCRIBED AS DEFECTS OCCURRING AT ANY PART OF THE LABORATORY SYSTEMS, FROM ORDERING TESTS TO REPORTING RESULTS AND APPROPRIATE INTERPRETATION AND REACTION TO THESE ERRORS. • ERRORS IN LABORATORY MAY OCCUR AS A RESULT OF THE FAILURE ON THE LABORATORY SYSTEMS AND PROCESSES.
- 5. SOME COMMON LABORATORY ERRORS • PATIENT ID ERROR • LOST SAMPLE • SAMPLE DELAYED IN TRANSIT • CONTAMINATED SAMPLES • WRONG TEST PERFORMED • TEST PERFORMED INCONSISTENT WITH THE WRITTEN PROCEDURE • PROFICIENCY TESTING ERROR • NO ACTION ON OUT OF RANGE CONTROLS • FALSE NEGATIVE/POSITIVE RESULT • LATE REPORTS • MISSING REPORTS • COMPLAINTS • LABORATORY ACCIDENT • “NEAR MISS”
- 6. equipment not properly maintained QC, EQA not performed test kits not stored properly transcription errors checks not done training not done or not completed written procedures not followed no written procedures individual responsibilities unclear Common causes of error
- 7. THE PATIENT Test Sample Collection Sample Transport Laboratory Analysis (Examination Phase) Report Creation Report Transport Pre-examination Phase Result Interpretation Post-examination Phase selection
- 8. PHASES OF ERRORS IN TESTING PROCESS TOTAL TESTING PROCESS IS TYPICALLY DIVIDED INTO THREE MAIN PHASES; 1. PRE-ANALYTICAL 2. ANALYTICAL 3. POST-ANALYTICAL • STUDIES HAVE DEMONSTRATED THAT A LARGE PERCENTAGE OF LABORATORY ERRORS OCCUR IN PRE AND POST-ANALYTICAL PHASES, WITH FEWER ERRORS OCCURRING DURING THE ANALYTICAL PHASE.
- 9. PRE-ANALYTICAL ERRORS EXAMPLES INCLUDED: • WRONG SAMPLE COLLECTED • SAMPLE MISLABELED OR UNLABELED • SAMPLE STORED INAPPROPRIATELY BEFORE TESTING • SAMPLE TRANSPORTED INAPPROPRIATELY • REAGENTS OR TEST KITS DAMAGED BY IMPROPER STORAGE
- 10. ANALYTICAL ERRORS EXAMPLES INCLUDED: • ESTABLISHED ALGORITHM NOT FOLLOWED • INCORRECT TIMING OF TEST • RESULTS REPORTED WHEN CONTROL RESULTS OUT OF RANGE • IMPROPER DILUTION AND PIPETTING OF SAMPLE OR REAGENTS • REAGENTS STORED INAPPROPRIATELY OR USED AFTER EXPIRATION DATE
- 11. POST ANALYTICAL ERROR EXAMPLES INCLUDED: • TRANSCRIPTION ERROR IN REPORTING • REPORT ILLEGIBLE • REPORT SENT TO THE WRONG LOCATION • REPORT NOT SENT
- 12. RISK OF LABORATORY ERRORS Inadequate or inappropriate patient care Inappropriate public health action Wasteful of resources Death Undetected communicable disease outbreaks ERROR
- 13. ANOTHER CLASSIFICATION • ERRORS CAN ALSO BE CLASSIFIED INTO FOLLOWING CATEGORIES: 1. DETERMINATE (SYSTEMIC) ERRORS: THE ERROR IS REPRODUCIBLE AND CAN BE DISCOVERED AND CORRECTED. 2. INDETERMINATE (RANDOM) ERRORS: CAUSED BY UNCONTROLLABLE VARIABLES, WHICH CAN NOT BE DEFINED/ELIMINATED.
- 14. PRECISION AND ACCURACY • TWO TERMS ARE COMMONLY ASSOCIATED WITH ANY DISCUSSION OF ERROR: "PRECISION" AND "ACCURACY". • PRECISION REFERS TO THE REPRODUCIBILITY OF A MEASUREMENT. • ACCURACY IS A MEASURE OF THE CLOSENESS TO TRUE VALUE. • THE CONCEPTS OF PRECISION AND ACCURACY ARE DEMONSTRATED BY THE SERIES OF TARGETS BELOW. • IF THE CENTER OF THE TARGET IS THE "TRUE VALUE", THEN A IS NEITHER PRECISE NOR ACCURATE. TARGET B IS PRECISE (REPRODUCIBLE) BUT NOT ACCURATE. THE AVERAGE OF TARGET C'S MARKS GIVE AN ACCURATE RESULT BUT PRECISION IS POOR. TARGET D DEMONSTRATES BOTH PRECISION AND ACCURACY - WHICH IS THE GOAL IN LAB.
- 17. DETERMINATE ERROR • DETERMINATE ERRORS ARE CAUSED BY FAULTS IN THE ANALYTICAL PROCEDURE OR THE INSTRUMENTS USED IN THE ANALYSIS. • THE NAME DETERMINATE ERROR IMPLIES THAT THE CAUSE OF THIS TYPE OF ERROR MAY BE FOUND OUT AND THEN EITHER AVOIDED OR CORRECTED. • DETERMINATE ERRORS ARE SYSTEMATIC ERRORS; THAT IS, THEY ARE NOT RANDOM. • A PARTICULAR DETERMINATE ERROR MAY CAUSE THE ANALYTICAL RESULTS PRODUCED BY THE METHOD TO BE ALWAYS TOO HIGH OR TOO LOW. SOMETIMES THE ERROR IS CONSTANT. • ALL RESULTS ARE TOO HIGH (OR TOO LOW) BY THE SAME AMOUNT.
- 18. • DETERMINATE ERRORS CAN BE ADDITIVE OR THEY CAN BE MULTIPLICATIVE. IT DEPENDS ON THE ERROR AND HOW IT ENTERS INTO THE CALCULATION OF THE FINAL RESULT. • THIS DETERMINATE ERROR COULD BE THE RESULT OF AN INCORRECTLY CALIBRATED BALANCE. • IF THE BALANCE IS SET SO THAT THE ZERO POINT IS ACTUALLY 0.5 MG TOO HIGH, ALL MASSES DETERMINED WITH THIS BALANCE WILL BE 0.5 MG TOO HIGH. • THE ERROR IS REPORTED AS THE ABSOLUTE ERROR, THE ABSOLUTE VALUE OF THE DIFFERENCE BETWEEN THE TRUE AND MEASURED VALUES.
- 19. • DETERMINATE ERRORS ARISE FROM SOME FAULTY STEP IN THE ANALYTICAL PROCESS. • THE FAULTY STEP IS REPEATED EVERY TIME THE DETERMINATION IS PERFORMED. WHETHER A SAMPLE IS ANALYZED 5 TIMES OR 50 TIMES, THE RESULTS MAY ALL AGREE WITH EACH OTHER (GOOD PRECISION) BUT DIFFER WIDELY FROM THE TRUE ANSWER (POOR ACCURACY).
- 20. INSTRUMENT ERRORS • FAILURE TO CALIBRATE, DEGRADATION OF PARTS IN THE INSTRUMENT, POWER FLUCTUATIONS, VARIATION IN TEMPERATURE, ETC. • IT CAN BE CORRECTED BY CALIBRATION OR PROPER INSTRUMENTATION MAINTENANCE. METHOD ERRORS • ERRORS DUE TO NO IDEAL PHYSICAL OR CHEMICAL BEHAVIOR-COMPLETENESS AND SPEED OF REACTION, INTERFERING SIDE REACTIONS, SAMPLING PROBLEMS • IT CAN BE CORRECTED WITH PROPER METHOD DEVELOPMENT. PERSONAL ERRORS • OCCUR WHERE MEASUREMENTS REQUIRE JUDGMENT, RESULT FROM PREJUDICE, COLOR ACUITY PROBLEMS. • IT CAN BE MINIMIZED OR ELIMINATED WITH PROPER TRAINING AND EXPERIENCE.
- 21. • ANALYST ERROR : THE PERSON PERFORMING THE ANALYSIS CAUSES THESE ERRORS. • THEY MAY BE THE RESULT OF INEXPERIENCE, INSUFFICIENT TRAINING, OR BEING “IN A HURRY”. • AN ANALYST MAY USE THE INSTRUMENT INCORRECTLY, • PERHAPS BY PLACING THE SAMPLE IN THE INSTRUMENT INCORRECTLY EACH TIME. • SETTING THE INSTRUMENT TO THE WRONG CONDITIONS FOR ANALYSIS. • IMPROPER USE OF PIPETTES, SUCH AS “BLOWING OUT” THE LIQUID FROM A VOLUMETRIC PIPETTE.
- 22. • SOME OTHER ANALYST-RELATED ERRORS ARE • CARELESSNESS • TRANSCRIPTION ERRORS, THAT IS, COPYING THE WRONG INFORMATION INTO A LAB NOTEBOOK OR ONTO A LABEL • CALCULATION ERRORS. • PROPER TRAINING, EXPERIENCE, AND ATTENTION TO DETAIL ON THE PART OF THE ANALYST CAN CORRECT THESE TYPES OF ERRORS.
- 23. INSTRUMENTATION ERRORS • NUMEROUS ERRORS INVOLVING INSTRUMENTATION ARE POSSIBLE, INCLUDING • USE OF IMPROPER OR EXPIRED STANDARD SOLUTIONS TO CALIBRATE INSTRUMENTS • INCORRECT INSTRUMENT ALIGNMENT • INCORRECT WAVELENGTH SETTINGS • INCORRECT READING OF VALUES, AND • INCORRECT SETTINGS OF THE READOUT (I.E., ZERO SIGNAL SHOULD READ ZERO). ANY VARIATION IN PROPER INSTRUMENT SETTINGS CAN LEAD TO ERRORS. • THESE PROBLEMS CAN BE ELIMINATED BY A SYSTEMATIC PROCEDURE TO CHECK THE INSTRUMENT SETTINGS AND OPERATION BEFORE USE. SUCH PROCEDURES ARE CALLED STANDARD OPERATING PROCEDURES (SOPS) IN MANY LABS. • THERE SHOULD BE A WRITTEN SOP FOR EACH INSTRUMENT AND EACH ANALYTICAL METHOD USED IN THE LABORATORY.
- 24. DETECTION OF SYSTEMATIC ERRORS 1. ANALYSIS OF STANDARD SAMPLES 2. INDEPENDENT ANALYSIS: ANALYSIS USING A "REFERENCE METHOD" OR "REFERENCE LAB“ 3. BLANK DETERMINATIONS 4. VARIATION IN SAMPLE SIZE: DETECTS CONSTANT ERROR ONLY
- 25. RANDOM (INDETERMINATE) ERROR • IT OCCURS ACCIDENTALLY OR RANDOMLY SO CALLED AS INDETERMINATE OR ACCIDENTAL OR RANDOM ERROR. ANALYST HAS NO CONTROL IN THIS ERROR. • NO IDENTIFIABLE CAUSE • ALWAYS PRESENT • CANNOT BE ELIMINATED • THE ULTIMATE LIMITATION ON THE DETERMINATION OF A QUANTITY. • EX. READING A SCALE ON AN INSTRUMENT CAUSED BY THE FINITE THICKNESS OF THE LINES ON THE SCALE; ELECTRICAL NOISE
- 26. INDETERMINATE ERRORS • INDETERMINATE ERRORS ARE NOT CONSTANT OR BIASED. • THEY ARE RANDOM IN NATURE • THEY ARE THE CAUSE OF SLIGHT VARIATIONS IN RESULTS OF REPLICATE SAMPLES MADE BY THE SAME ANALYST UNDER THE SAME CONDITIONS. • SOURCES OF RANDOM ERROR INCLUDE THE LIMITATIONS OF READING BALANCES, SCALES SUCH AS RULERS OR DIALS, AND ELECTRICAL “NOISE” IN INSTRUMENTS. • FOR EXAMPLE, A BALANCE THAT IS CAPABLE OF MEASURING ONLY TO 0.001 G CANNOT DISTINGUISH BETWEEN TWO SAMPLES WITH MASSES OF 1.0151 AND 1.0149 G.
- 27. • THESE RANDOM ERRORS CAUSE VARIATION IN RESULTS, SOME OF WHICH MAY BE TOO HIGH AND SOME TOO LOW. • INDETERMINATE ERRORS ARISE FROM SOURCES THAT CANNOT BE • CORRECTED • AVOIDED • IDENTIFIED, IN SOME CASES. • HOWEVER, BECAUSE INDETERMINATE ERROR IS RANDOM, THE ERRORS WILL FOLLOW A RANDOM DISTRIBUTION. • THIS DISTRIBUTION CAN BE UNDERSTOOD USING THE LAWS OF PROBABILITY AND BASIC STATISTICS. THE EXTENT OF INDETERMINATE ERROR CAN BE CALCULATED MATHEMATICALLY.
- 28. IN OTHER WORDS • ACCURATE MEASUREMENTS HAVE LITTLE DETERMINATE ERROR. • DETERMINATE ERROR DEGRADES ACCURACY BUT HAS NO EFFECT ON PRECISION. • PRECISE MEASUREMENTS HAVE LITTLE INDETERMINATE ERROR. • INDETERMINATE ERROR DEGRADES PRECISION BUT IT DOES NOT INFLUENCE ACCURACY.