Quality Control in the Laboratory PDF

Quality Control in the laboratory Quality Control is the process of detecting errors. Errors will occur even in the best of laboratories. Good quality control will provide the clinician with a high degree of confidence in the clinical data generated by...

Quality Control in the laboratory Quality Control is the process of detecting errors. Errors will occur even in the best of laboratories. Good quality control will provide the clinician with a high degree of confidence in the clinical data generated by the laboratory. Diagnostic testing accounts for 60 – 70% of all medical decision making. Consequently, the quality of laboratory work is of the utmost importance in ensuring patients are correctly diagnosed and administered the appropriate treatment. Therefore, it is a routine requirement for a lab to perform quality control checks alongside each batch of patient samples tested. Consequences of Unreliable Performance – Patient misdiagnosis – Delays in treatment – Increased costs Labs use two complementary systems for controlling quality these two forms are complementary activities: Internal Quality Control (IQC) involves the daily monitoring of the precision and accuracy of the analytical method of quality control sera with known values. External Quality Assessment (EQA) is a comparison of performance to other laboratories, using sera with unknown concentrations. Maintaining the long-term accuracy of the analytical methods. Quality Assurance Quality Assurance refers to the systems or procedures in place to prevent errors occurring. The term should not confused with quality control. A good laboratory will have both these systems working together to ensure the reliability of the test results, to give the best patient care. Error Classification Error defined as deviation from accepted true values. – Pre-analytical: Errors occurring before the sample reaches the laboratory directly affect the quality and usefulness of the result – Analytical: Errors occurring during the analysis of the sample – Post-analytical: Errors occurring after the analysis Pre-analytical error types: Patient preparation. For example, fast prior to a blood glucose test, stress and anxiety can cause elevations in urinary protein levels. Improper collection of the blood sample can lead to erroneous results For example, Sample haemolysis will affect tests such as LDH, potassium and inorganic phosphate, Collection of insufficient volume of sample may mean that the lab is not be able to carry out all tests requested, Collection timing is also important, particularly when looking at analyte levels in a 24 hour urine sample Container for the preparation of serum and plasma samples, EDTA tubes are unsuitable for calcium tests, Fluoride tubes for blood glucose tests to inhibit glycolysis stored appropriately prior to testing For example, if a sample is left out overnight at room temperature, then falsely elevated levels of potassium, phosphate and red cell enzymes, such as LDH and AST, may occur due to leakage of intracellular fluid into the plasma Unstable analytes (NEFA) require fast handling and analysis Other Factors such as the age and sex of the patient for which the normal levels are different in males and females and in paediatric / adult / geriatric samples. Dietary effects, For example, the amount of carbohydrate and fat in the diet can affect the levels of blood lipids while a diet high in protein can place stress on the kidneys, affecting the results of kidney function tests. When the sample is taken For example, an early morning urine sample is advised for early pregnancy testing. Patient posture as Urinary protein levels tend to be lower in bed-ridden patients. The effects of exercise strenuous exercise can cause elevations in levels of inflammatory markers such as CK and CRP. a patient’s medical history, Any existing heart disease, diabetes or medication should be made known. Pregnancy, Physiological changes that occur during pregnancy can alter the normal ranges for many lab tests. The effects of drugs and alcohol, Levels of liver enzymes may be affected. Analytical error types: Samples may be incorrectly labelled (barcoded) or a liquated, processed for the wrong test profile, prepared / centrifuged incorrectly, stored inappropriately. May also involve the use of glassware, pipettes and balances incorrectly, contaminated, and poorly calibrated, In addition, the reuse of pipette tips can also lead to errant results. May also occur as a consequence of the reagents, calibrators or controls in use of poor quality, used outside the shelf-life / working stability period, prepared incorrectly (e.g. reconstitution of lyophilised materials),stored inappropriately, At the incorrect temperature In poorly maintained fridges / freezers. May also occur because of an incorrect application / assay protocol used. May also be due to the instrument in use, there may be operational limitations of the system, involving temperature control, read times, mixing, carry-over. On the other hand, instruments may be badly maintained worn tubing, optics, cuvettes, and probes. In addition, several other factors can result in analytical errors such as calculation errors and Dilution errors (the assay linearity), human factor tiredness / carelessness / stress. Post-analytical Errors This phase involves the prompt and correct delivery of the correct report on the correct patient to the correct doctor and how that doctor interprets the data to the full benefit of the patient. How often should we run QC? How often a laboratory should run QC will be very much dependent on the individual lab and their processes. Many factors will determine this, such as: The quantity of tests run per day Which tests are higher risk and have a higher impact if results are erroneous Experience and competency of laboratory staff The instrument, reagent and method in use Available time between QC evaluations Which assays are more stable compared to others? It is often recommended that QC is run at the beginning and end of each analytical run or when a batch of reagents is changed. ISO 15189 regulations however do not state a recommended QC frequency but they do recommend that: “Quality Control materials shall be periodically examined with a frequency that is based on the stability of the procedure and the risk of harm to the patient from an erroneous result.” Laboratories must therefore consider all of the above factors and determine how often they should be running QC to ensure confidence in the results produced.