Practical clinical chemistry Marks Lab reports Quizzes Midterm Final Mr.Naser Abu. Sha’ban

0bjectives of this course: introduction the fundamental concepts of clinical chemistry Revision for quality control and apply it practically on the laboratory test. Training on pipette using and how to calibrate it. Understanding the clinical significant, principle, procedure and other technical skills related to chemical laboratory test.

Definition of clinical chemistry clinical chemistry is a basic science that utilizes the quantitative analysis on the body fluids such as blood, urine as well as feces, tissue, calculi in order to study human beings in various stages of health and to be used by physician in diagnosis and treatment of disease. clinical chemistry concerned with the analysis and their techniques but chemical pathology concerned with the causes and mechanism of disease and management of patient (treatment).

The results of most clinical biochemical investigations are expressed Quantitatively or as percentage In the case of enzyme measurements, as an activity

Clinical chemistry focus on

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 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). daily monitoring of quality control sera 2. External Quality Assessment (EQA). comparing of performance to other laboratories.

The reproducibility of your results 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

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 Specificity 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

Concept of clinical chemistry Analyte: The constituent or characteristic of the sample to be measured. Assay: 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

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 13s represents a control rule which is manifested when one control observation exceeds the ±3s control limits

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

Rule 12s This is a warning rule that is violated when a single control observation is outside the ±2s limits. This rule warns that random error or systematic error may be present in the test system. Must then evaluate the13S rule

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

Rule R4s This rule identifies random error only One control exceeds the mean by –2SD, and the other control exceeds the mean by +2SD 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 +2.8s above the mean and Level II is -1.3s below the mean. The total difference between the two control levels is greater than 4s (e.g. [+2.8s – (-1.3s)] = 4.1s).

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

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

Random Erorrs

Systematic Errors

Normal curve

An example of slight bias

An example of positive bias

Trend

Shift

Differentiate between control, standard and calibrators: 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 Are samples of known concentration used to adjust analyzer or instrumentation parameters. The value assigned for each constituent are to be determined by a reference method

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