Internal quality control in blood bank testing
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Internal quality control is essential for blood bank testing to continuously monitor laboratory work and results. It involves running both quantitative and qualitative controls to check for issues like drift, dispersion, or shifts that could indicate problems. Quantitative tests have controls run to establish mean, standard deviation, and target ranges using statistical analysis. Qualitative rapid card tests have positive and negative controls run daily. Equipment and reagents also have defined internal quality checks run daily or weekly. Control values are monitored using Levy-Jennings charts and Westgard rules to ensure precision and accuracy and identify any issues requiring troubleshooting or corrective action.
Internal quality control in blood bank testing
- 1. Internal Quality Control In Blood Bank Testing Internal Quality Control (IQC) is the backbone of any quality assurance program. Internal quality control is the set of procedures undertaken by the staff of a laboratory for continuously and concurrently assessing laboratory work and the emergent results, to decide whether they are reliable enough to be released. It is meant to allow laboratory technicians to check their own performance and help them to monitor the reliability of their technique. It maintains day to day working objectively and detects any deviation very early like Drift or trend - Seen when the control value moves progressively in one direction from the mean for a minimum of three (3) days. Suggests that a problem is gradually developing, such as deterioration of a reagent or control. Dispersion – Increase in Random Errors and Lack of Precision. Suggests inconsistency of technique or fluctuations in instrumentation function. Shift – Abrupt changes observed when a problem develops suddenly. May be due to instrument malfunction or an error in technique. QUALITY MANAGEMENT in blood transfusion service is concerned with every aspect of transfusion practice and applies to all activities of a blood transfusion service. It involves identification and election of prospective blood donors, adequate ollection of blood, preparation of blood components, quality laboratory testing and ensuring the safest and most appropriate use of blood/blood components. When testing of blood & its components is performed, test may either be classified as: QUANTITATIVE: Measures the amount of substance present like in TTD (ELISA,MILUMINESCENCE), Final products and Donor selection parameters. QUALITATIVE: Determines whether the substance being tested is present or absent like in Blood rouping, rapid card tests etc.Internal quality control programme try to make things more objective than subjective and to reduce interpersonal or inter organization errors/differences. List of Qualitaive(QL) and Quantitaive (QN) tests done in blood bank TESTS FOR DONOR ELECTION TESTS OF COLLECTED BLOO PRODUCT TEST OF FINAL PRE TRANSFUSION SEROLOGICAL TESTS DONE Hemoglobin (QN) HIV(QN)/(QL-CARD TEST) Hemoglobin (QN) Bloodgrouping (QL) Platelet count (QN) HBs Ag (QN)/ (QL-CARD TEST) PCV(QN) Cross Matching (QL) SerumAlbumin HCV TEST) Platelet count (QN) Antibody screening / (QN)/ (QL-CARD (plasmaidentification (QL) Donors) (QN) VDRL/RPR(QL) pH (QN) Direct (QL) Coombs Test
- 2. MP (QL) TRBC (QN) Indirect Coombs Test (QL) TLC (QN) Factor VIII (QN) Fibrinogen (QN) PTTK (QN) Pyogenic Culture (QN) EQUIPMENT/REAGENTS WHICH NEED IN-HOUSE CHECKS (IQC) ELISA Reader/Kits Blood grouping equipment/Reagents Cross Matching cards/Antibody screening Hematology analyzer/Reagents pH meter Rapid cards/RPR/MP Coagulation analyzer Internal Quality Control for Quantitative Tests Implementing QC program for Quantitative tests operates on the following steps: Select quality controls. Collect at least 20 control values over a period of 20- 30 days for each level of control. Perform statistical analysis. Develop Levey-Jennings chart. Monitor control values using the Levey-Jennings chart and/or Westgard rules. Take immediate corrective action, if needed. Record actions taken. SELECTING CONTROL MATERIALS/CALIBRATORS A calibrator has a known concentration of the substance (analyte) being measured. Calibrator is used to adjust instrument, kit, test system in order to standardize the assay. Calibrator is not a control. A control has a known range of the analyte. Usually 2 or 3 levels of controls are used based on the number of tests run daily for a particular analyte. The controls should be run along with patient sample and are used to validate day to day reliability of the test system. Characteristics of Control materials Different values covering all Medical decision points Similar to the test specimen (matrix) Available in large quantity Stored in small aliquots Ideally, should last for at least 1 year Managing Control materials
- 3. Sufficient material from same lot number/ generation number or serum pool for one year’s testing May be frozen, freeze dried, or chemically preserved Requires very accurate reconstitution if this step is necessary Always store as recommended by the manufacturer Sources of QC samples Appropriate diagnostic sample Obtained from: Another Laboratory EQA provider Commercial product Types of Control materials ASSAYED: Mean calculated by the manufacturer Must verify in the laboratory UNASSAYED: Less expensive Must perform data analysis “HOMEMADE” OR “INHOUSE”: Pooled sera collected in the laboratory Characterized Preserved in small quantities for daily use ANALYSIS OF QC RESULTS Analytical tools are needed for the analysis of the QC data. Basic Statistical skills are required for the urpose and form an important skill for the laboratory personnel. Levy Jennings’s (LJ) chart should be used to plot daily QC values. It indicates the changes in trends and shifts of the laboratory performance. Westgard rules should be used to interpret daily QC values. The level of QC applied in the laboratory varies according to the number of specimens analyzed per day. A data set of at least 20 points should be obtained over a 30 day period. These data points are used to calculate mean, standard deviation, coefficient of variation; determine target ranges. It is made sure that all the procedural variation is represented including different operators, different times of the day. Variability in the data is determined to establish the acceptable range. MEASUREMENT OF VARIABILITY – A certain amount of variability will naturally occur when a control is tested repeatedly. Variability is ffected by operator technique, environmental conditions, and the performance characteristics of the assay method. The goal is to differentiate between variability due to chance from that due to error. The terms used to describe variability are: Range, Variance, Standard Deviation, Coefficient of Variation.
- 4. MEASUREMENT OF CENTRAL TENDENCY – Data are frequently distributed about a central value or a central location. The measures are – MEDIAN - The value at the center(midpoint) of the observations MODE – The value which occurs with the greatest frequency MEAN – The calculated average of the values CALCULATION OF MEAN – done using the standard formula keeping out of calculation the outliers (values which fall outside the manufactures supplied control range). MEAN FOR ELISA TEST The calculation of mean is especially useful for ELISA test used in blood banks. The optical density (OD) values and cut off (CO) for controls for each assay run is measured. The ratio of OD to CO (OD/CO) is calculated and considered as a single data point. This ratio standardizes the data and is used to calculate the laboratory mean. where X = OD/CO (OD- optical density; CO - cut off for control) NORMAL DISTRIBUTION; X AXIS – RATIO OF OD/CO; YAXIS – FREQUENCY MEAN FOR HEMATOLOGY PARAMETERS where X = value of test eg. Hb, Platelet count etc ACCURACY AND PRECISION The degree of fluctuation in the measurement is indicative of the “precision” of the assay. The closeness of measurements to the true value is indicative of the “accuracy” of the assay. Quality control is used to monitor both the precision and the accuracy of the assay in order to provide reliable results. RANGE Refers to the difference or spread between the highest and lowest observations. It is the simplest measure of dispersion. It makes no assumption about the sahpe of he distribution or the central tendency of the data. VARIANCE (S ) 2 Is a measure of variability about the mean. It is calculated as the average squared deviation from the mean. S= ?(X-X¯) = 2 2 mg /dl 2 2 N-1 DEGREES OF FREEDOM Represents the number of independent data points that are contained in a data set. The mean is calculated first, so the variance calculation has lost one degree of freedom (n-1). CALCULATION OF STANDARD DEVIATION The standard deviation is the square root of the variance; it is the square root of the average squared deviation
- 5. from the mean. SD is commonly used (rather that the variance) since it has the same units as the mean and the original observations. SD is the principle calculation used in the laboratory to measure dispersion of a group of values around a mean. Laboratories use the +/- 2SD criteria for the limits of the acceptable range for a test meaning that when the QC measurement falls within that range, there is 95.5% confidence that the measurement is correct. Only 4.5% of the time will a value fall outside of that range due to chance; more likely it will be due to error. S = square root of (X-X¯) = mg/dl N-1 S = square root of Variance CALCULATION OF COEFFICIENT OF VARIATION The CV is the standard deviation expressed as a percentage of the mean. Ideally it should be less than 5%. CV = SD/mean X 100 2 MONITORING OF QC DATA Levy Jennings’s (LJ) chart should be used to plot daily QC values for each run and make decisions regarding acceptability of run. Monitoring should be done to evaluate the precision and accuracy of repeated measurements. Charts needs to be reviewed at regular intervals to take necessary action and documented. LEVEY-JENNINGS CHART It is a graphical method for displaying control results and evaluating whether a procedure is in-control or out-ofcontrol. The control values are plotted versus time. Lines are drawn from point to point to accent any trends, shifts or random excursions. An example of a Levey-Jennings chart with upper and lower limits of one and two times the standard deviation. The control values in a L-J chart should be ideally clustered about the mean (+/- 2SD) with little variation in the upward or downward direction. IMPRECISION – large amount of scatter about the mean usually cause by error in the technique INACCURACY – may be seen as a trend or a shift, usually caused by change in the testing process. RANDOM ERROR - No pattern. Usually poor technique, malfunctioning equipment. WESTGARDRULES Multirule QC uses a combination of decision criteria, or control rules, to decide whether an analytical run s incontrol or outof- control. The well-known Westgard multirole QC procedure uses 5 different control rules to judge the acceptability of an analytical run. By comparison, a single-rule QC procedure uses a single criterion or single set of control limits, such as a Levey-Jennings chart with control limits set as either the mean plus or minus 2 standard deviations (2s) or the mean plus or minus 3s. “Westgard rules” are generally used with 2 or 4 control measurements per run, which means they are appropriate when two different control materials are measured 1 or 2 times per material, which is the case in many chemistry applications. Some alternative control rules are more suitable when three control materials are analyzed, which is common for applications in hematology, coagulation, and immunoassays. 1 Refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as 3s the mean plus 3s and the mean minus 3s. A run is rejected when a single control measurement exceeds the mean plus 3s or the mean minus 3s control limit. 1 Refers to the control rule that is commonly used with a Levey-Jennings chart when the control limits are set 2s
- 6. as the mean plus/minus 2s. In the original Westgard multirule QC procedure, this rule is used as a warning rule to trigger careful inspection of the control data by the following rejection rules. 2 Reject when 2 consecutive control measurements exceed the same mean plus 2s or the same mean minus 2s 2s control limit. R Reject when 1 control measurement in a group exceeds the mean plus 2s and another exceeds the mean 4s minus 2s. 4 Reject when 4 consecutive control measurements exceed the same mean plus 1s or the same mean minus 1s 1s control limit. 10 Reject when 10 consecutive control measurements fall on one side of the mean. x When a rule is violated; in case of WARNING RULE use other rules to inspect the control points. In case of REJECTION RULE (Out of control) immediately stop testing – identify and correct the problem – repeat testing on patient samples and controls – do not report patient results until problem is solved and controls indicate proper performance. For solving out of control problems there should be definite policies and procedures for remedial action; troubleshooting guides and alternatives to run rejection Internal Quality Control for Qualitative Tests Qualitative test (rapid card) for transfusion transmitted disease with built in controls are adequate rovided the kit has been qualified with at least one positive and one negative control from external sources (can e in-house also). These shall be validated by two qualified personnel and documented. Qualitative test in blood group serology is carried out daily and documented as follows: Sr. No Reagents Performance Frequency Of Testing Anti Human Appearance, Reactivity And Specificity 1. Serum Blood Grouping Appearance,Specificity,Avidity,Reactivity,Potency 2. Serum Antibody 3. Screening 4. 5. And Appearance , ReactivityAnd Specificity Daily Daily Lot Reverse Grouping Cells Syphilis (Rapid Positive And Negative Control (External) Card) Normal Salinee Appearance, Nacl Content, Ph, Haemolysisl Each TestN Daily Daily Equipment/Reagents Sr. No Equipment Performance 1. Temperature Recorder 2. Refrigerator Compare against thermometer Compare against thermometer 3. Gen Centrifuge RPM 4. Blood bag Centrifuge Every Frequency Of Testing Temperature Daily Daily Standardize speed before initial use RPM Fortnight
- 7. 5. 6. 7. 8. Water bath Auto-Clave Cell counter Balance Weights 5mg-100g 9. Platelet Agitator 10. Laminar Flow hood Gen/Electronic thermometer Observe temp Observe temp Calibration Reference sample Analytical control. 6 Monthly Frequency of agitation Air pressure, clean Observe temperature Daily Daily Daily Monthly Monthly Daily IMPLEMENTATION OF INTERNAL QUALITY CONTROL PROGRAM Establish written policies and procedures Assign responsibility for monitoring and reviewing Train staff Obtain control materials Collect data Set target values (mean, SD) Establish and implement troubleshooting and corrective action protocols Establish and maintain system for documentation