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
Shift – Abrupt changes observed when a problem develops suddenly. May be due to instrument malfunction or
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
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
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 OF COLLECTED BLOO
TEST OF FINAL PRE
SEROLOGICAL TESTS DONE
Platelet count (QN)
HBs Ag (QN)/ (QL-CARD
Cross Matching (QL)
Antibody screening /
Indirect Coombs Test
Factor VIII (QN)
Pyogenic Culture (QN)
EQUIPMENT/REAGENTS WHICH NEED IN-HOUSE CHECKS (IQC)
Blood grouping equipment/Reagents
Cross Matching cards/Antibody screening
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
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:
Types of Control materials ASSAYED:
Must verify in the laboratory
Must perform data analysis
“HOMEMADE” OR “INHOUSE”:
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.
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.
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 )
Is a measure of variability about the mean. It is calculated as the average squared deviation from the mean.
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
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
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
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
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
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.
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
1 Refers to a control rule that is commonly used with a Levey-Jennings chart when the control limits are set as
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
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 control limit.
R Reject when 1 control measurement in a group exceeds the mean plus 2s and another exceeds the mean
4 Reject when 4 consecutive control measurements exceed the same mean plus 1s or the same mean minus
1s control limit.
10 Reject when 10 consecutive control measurements fall on one side of the mean.
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
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:
Frequency Of Testing
Appearance, Reactivity And Specificity
And Appearance , ReactivityAnd Specificity
Positive And Negative Control (External)
Normal Salinee Appearance, Nacl Content, Ph, Haemolysisl
1. Temperature Recorder
Compare against thermometer
Compare against thermometer
3. Gen Centrifuge
4. Blood bag
Frequency Of Testing
Standardize speed before initial
9. Platelet Agitator
10. Laminar Flow hood
Calibration Reference sample
Frequency of agitation
Air pressure, clean
IMPLEMENTATION OF INTERNAL QUALITY CONTROL PROGRAM
Establish written policies and procedures
Assign responsibility for monitoring and reviewing
Obtain control materials
Set target values (mean, SD)
Establish and implement troubleshooting and corrective action protocols
Establish and maintain system for documentation