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QC for Cobas 6000

Introduction and analysis of quality control for six analytes processed using Cobas 6000 instrument
by

Akshay Deshpande

on 1 December 2013

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Transcript of QC for Cobas 6000

Quality Control For
Cobas 6000
Akshay Deshpande
2011A9PS275U
Glucose
Cholesterol
Alkaline Phosphatase
CRP
Sodium ion
Ferritin
The e601 module is a multi-test immunoassay analyser with random access capability. It has a capacity to carry out up to 170 tests per hour. It can be used to analyse samples such as hormones. It works on the principle of electrochemiluminescence
Electrochemiluminescence is a process in which highly reactive species are generated from stable precursors at the surface of an electrode. These highly reactive species react with one another, producing light
This light which is emitted can be analysed with the help of spectroscopy and compared with standard values to measure the quantity of a particular analyte in the test sample
It is made up of two subunits. One is the photometric subunit and the other is the ISE subunit.
The photometric subunit provides the analyser with a flexible photometric method based on the principle of bichromatic analysis. It can process up to 600 in vitro tests per hour.
The ISE subunit provides the analyser with a potentiometric method for assaying of Na+, K+ and Cl- ions from samples. It can process up to 200 samples per hour

It has two different modules available namely, c501 and e601 modules

c501 module is a chemistry analyser
The e601 module is an immunoassay analyser

Cobas 6000

Shifts in QC data represent a sudden and dramatic positive or negative change in test system performance. Shifts may be caused by:
Sudden failure or change in the light source
Change in reagent formulation
Change of reagent lot
Major instrument maintenance
Sudden change in incubation temperature (enzymes only)
Change in room temperature or humidity
Failure in the sampling system
Failure in reagent dispense system
Inaccurate calibration/recalibration

A trend indicates a gradual loss of reliability in the test system

Trends are usually subtle and causes of trending may include:
Deterioration of the instrument light source
Gradual accumulation of debris in sample/reagent tubing
Gradual accumulation of debris on electrode surfaces
Aging of reagents
Gradual deterioration of control materials
Gradual deterioration of incubation chamber temperature (enzymes only)
Gradual deterioration of light filter integrity
Gradual deterioration of calibration


Systematic errors occur by a deviation of QC results from the mean of the control values

The change in the mean may be gradual and demonstrated as a trend in control values or it may be abrupt and demonstrated as a shift in control values


When quality control results are plotted on a Levey-Jennings chart, an assessment of the runs can be made from the chart itself. Errors can be spotted more easily and can also be classified more easily into systematic errors or random errors

For example, consider the mean for a particular potassium control to be 4.1 mmol/L and the standard deviation to be 0.1 mmol/L. The ranges for ±1s, ±2s and ±3s quality control limits in the Levey-Jennings chart can be calculated as follows

Coefficient of variance or simply CV, is defined as the ratio between the standard deviation and the mean of given data
CV is independent of the unit in which the measurements are taken
Hence, CV can be used to compare data with different measurement units from each other and also data with greatly varying means

Imprecision may result due to the chemistry involved or due to a malfunction
If it is a malfunction, steps must be taken to correct the problem
It is desirable to get precise results, especially for tests that are repeated regularly on the same patient to track treatment or disease progress

Quantifies how close numerical values (i.e. QC values) are in relation to each other
Standard deviation is calculated from the same data used to calculate the mean
It provides the laboratory an estimate of the precision of the testing method in use
The repeatability of a test may be consistent (low standard deviation, low imprecision) or inconsistent (high standard deviation, high imprecision)

Quality control in the medical laboratory is a statistical process used to monitor and evaluate the analytical process that produces patient results
QC results are used to validate whether the instrument is operating within pre-defined specifications, inferring that patient test results are reliable

Quality Control

A random error is any deviation away from an expected result
For QC results, any positive or negative deviation away from the calculated mean is defined as random error
There can be acceptable random errors as defined and quantified by standard deviation
There can also be unacceptable random errors that are any data points outside the acceptable limits of the data (e.g., a data point outside the ±3s limits)

The Levey-Jennings chart is used to graph successive (run-to-run or day-to-day) quality control values
A chart is created for each test and level of control
The first step is to calculate decision limits. These limits are ±1s, ±2s and ±3s from the mean.

How well a series of measured values agree with each other

The repeatability of a particular result
The result of an individual measurement of a quantifiable property

The known and accepted value of a quantifiable property

Accuracy
How well a measured value agrees with a the true value

Precision
True Value
Measured Value
Mean
The mean (or average) is the laboratory’s best estimate of the analyte’s true value for a specific level of control
To calculate a mean for a specific level of control, we first add all the values collected for that control. Then we divide the sum of these values by the total number of values
Quality Control

To ensure accuracy and precision of results:

Daily quality control runs
Constant monitoring of instrument
Routine calibrations
Routine maintenance

Accuracy vs. Precision
Mean
Standard Deviation
Standard Deviation
Coefficient of Variance
Levey-Jennings Chart
Levey-Jennings Chart
Levey-Jennings Chart
Levey-Jennings Chart
Levey-Jennings Chart
Systematic Errors
Trends
Shifts
Random Errors
Cobas 6000
c501 module
e601 module
Analytes I have chosen…
Standard Deviation
Standardising the Instrument
Manufacturer
Machine Calibration
Levey-Jennings Charts
Optics
Stability of light source
Pipetting
Carryover
Voltage
{
Precision
Accuracy
Internal Quality Control
External Quality Assessment
Westgard Rules
Got quality control related data from the instrument for each analyte
My work...
Calculated the unbiased population mean and standard deviation for the data collected
Using the analysed data, I prepared Levey-Jennings charts for each of the analytes
Analysed the same and cross referenced the abnormalities to check for the corrective actions taken
Mean
S.D.
CV
Glucose
Cholesterol
Alkaline Phosphatase
CRP
Ferrittin
106
246.66
92.97
179.46
25.34
196.20
14.17
40.95
92.33
213.71
113.55
137.05
Na
+
4.2
11.23
3.96
4.55
3.38
6.86
3.64
3.82
5.9
11.65
6.39
5.45
0.377
0.927
2.66
2.26
3.36
1.53
2.96
1.11
1.67
14.74
6.59
7.51
Thank You
Full transcript