Quality Assessment The goal of laboratory analysis is

Quality Assessment The goal of laboratory analysis is to provide the accurate, reliable and timeliness result Quality assurance The overall program that ensures that the final results reported by the laboratory are correct. QA involves in every step in the analysis process from the initial ordering of a test and the collection of the patient sample (pre analytic), analysis of the sample (analytic), and finally the distribution of result to the proper destination ( post analytic). Quality control A statistical process used to monitor and evaluate analytical process that produces patient results

How can Analytical Quality be Controlled? 1. Internal Quality Control (IQC). T daily monitoring of quality control sera 2. External Quality Assessment (EQA). T comparing of performance to other laboratories.

Quality Control used to monitor the accuracy and precision of the assay Accuracy The closeness of the estimated value to the true mean Precision The reproducibility of your results

Specificity Sensitivity the ability of a diagnostic test to detect very small amounts of the analyte The other is the ability of a test to detect truly infected individuals. Ability to exclude false negatives It is the ability of a method to identify all samples which do not contain the substance being detected (identify non-infected individuals correctly). Ability to exclude false positive

Linearity A quantitative analytical method is said to be linear when: the measured value from a series of sample solutions is linearly proportional to the actual concentration or content of the analyte (true value) in the sample solutions

Standard deviation: the dispersion of a set of data from its mean. X: is the mean Xi: is an individual measurement ∑: is the operation of summation Mean: the average values (the central point).

The coefficient of variation (CV) Ø Is the SD expressed as a percentage of the mean (average) and is more reliable means for comparing the precision at different concentration level of units. The precision of method varies inversely with the CV; the lower the CV the greater the Precision. Range of CV < 5 -10% to consider the method is precise.

Levey Jennings Chart (L-J chart) A Levey Jennings Chart, is plotted with lines representing the mean and the SDs above and below, against a suitable time interval. Most laboratories will run a series of quality control sera, covering the full clinical range(Put up the IQC specimen for at least 20 or more assay runs) and not rely on a single control with only normal values. A chart will be established for each analyte and each level of control run. The values obtained are plotted on the chart allowing a rapid visual assessment of performance to be made.

L-J chart When the results are plotted, an assessment can be made about the quality of the run. The technologist/technician performing the test should look for systematic error and random error

Westgard Rules ¤ There are six basic rules in the Westgard scheme. ¤ These rules are used individually or in combination to evaluate the quality of analytical runs. ¤ Most of the quality control rules can be expressed as NL where N represents the number of control observations to be evaluated and L represents the statistical limit for evaluating the control observations. ¤ Thus 13 s represents a control rule which is manifested when one control observation exceeds the ± 3 s control limits

Rule 13 s ¤ One QC result outside ± 3 s ¤ This rule identifies unacceptable random error or possibly the beginning of a large systematic error.

Rule 12 s ¤ This is a warning rule that is violated when a single control observation is outside the ± 2 s limits. ¤ This rule warns that random error or systematic error may be present in the test system.

Rule 22 s ¤ This rule identifies systematic error only. ¤ The criteria for this rule are: • Two consecutive QC results Greater than 2 s on the same side of the mean • Or Both controls in the same run exceed ± 2 SD ¤ Patient results cannot be reported. ¤ Requires corrective action

Rule R 4 s ¤ This rule identifies random error only ¤ One control exceeds the mean by – 2 SD, and the other control exceeds the mean by +2 SD ¤ The difference between the two results will therefore exceed 4 SD. ¤ For example, assume both Level I and Level II have been assayed within the current run. Level I is +2. 8 s above the mean and Level II is -1. 3 s below the mean. The total difference between the two control levels is greater than 4 s (e. g. [+2. 8 s – (-1. 3 s)] = 4. 1 s).

Rule 41 s ¤The criteria which must be met to manifest this rule are: • Four consecutive QC results for one level of control are outside ± 1 SD on the same side of the mean, or • both levels of control have 2 consecutive results that are outside ± 1 SD. ¤This allows the detection of systemic error

¤These rules are violated when there are: ¤Ten consecutive QC results for one level of control are on one side of the mean, or ¤both levels of control have five consecutive results that are on the same side of the mean (no requirement for SD size). ¤This allows the detection of systemic error.

Normal curve

Systematic Errors within the test system of methodology Affect the accuracy of result Include: incorrect instrument calibration Reagent that lost their activity Ex: Shift and Trend Random Errors Occur without prediction or regularity Affect measurement of precision and causes data to be scattered more. Occure as the result of carelessness and when taking short cuts in procedures Unprecise pipetting

Random Erorrs

Systematic Errors

Shift: Is defined as a drift of values from one level of the control chart to another, which may be sudden or gradual and may be due to failure to recalibrate when changing lot numbers of reagent during an analytical process.

Shift

Trend: Is the continuous movements in one direction over six or more consecutive values. Trends are difficult to detect without continual charting, and may start on one side of the mean and move across it or it can occur entirely on one side of the mean this problem is usually due to deterioration of reagents or light source of the instrumentations.

Trend

Differentiate between control, standard and calibrators: Controls A solution that contain the same constituent as those being analyzed in the patient sample Most are commercially produced from pooled sera Samples of known concentration that are used to monitor the accuracy and precision of an analyzer and assay Range Calibrators and standards Are samples of known concentration used to adjust analyzer or instrumentation parameters. It is used to calculate the concentration of an analyte/s in the sample. Value

Concept of clinical chemistry Analyte: The constituent or characteristic of the sample to be measured. Assay: to analyze a sample of a specimen to determine the amount, activity, or potency of a specific analyte or substance. Run: A series of measurements Range: The difference between the largest and smallest observed value of a quantitative characteristic or statistical limits. Lyophilization: Freeze- dried. Concentration: A measure of the amount of dissolved substance per unit of volume. Out of control: indicates that the analysis of patient samples is unreliable.

Analytical methods used in clinical chemistry Spectrophotometry Electrochemistry photometry Other Chromatography Electrophoresis