Practical Clinical Chemistry: Core Concepts, Lab Techniques

Clinical laboratory science consists of various specialties such as clinical

chemistry, hematology, immunology, microbiology, serology, toxicology

and pathology

Clinical Chemistry is an exciting field that combines analytics and

instrumentation with information technology and management of workflow,

staff efficiencies and high volume automation. The field is ever-changing

and demands staff have skills in the methodologies and their limitations,

technology and troubleshooting equipment, as well as management and ability

to adapt operations to evolving clinical needs. At the heart, the laboratory is

a service to the physician providing test results that are critical to diagnosing

and managing patients. But, the laboratory is also a vital member of the

healthcare team and gets involved in utilization, operational efficiencies and

improving patient outcomes.

course contents

Introduction to clinical chemistry

analytes that are measured using clinical chemistry tests

Types of biologic specimens that may be used  for testing

How the results of tests are interpreted

Measurement principales

optical (photometric)

and electrochemical (potentiometric) – that are most often used to

determine concentrations of analytes in the clinical chemistry laboratory.

he difference between an endpoint and a rate reaction

the principle of potentiometric measurement

Chemical reactions of analytes produce products that can be detected

by using optical methods; changes in light absorbed, scattered or

emitted by these products are used to determine the concentration of

the analyte.

2.  In potentiometric methods, changes in concentrations of ions are

sensed as potential differences between two electrodes.

3.  Calibrators, solutions of known concentration, are used to establish the

relationship between the magnitude of an optical or electrical signal

and the corresponding concentration of analyte.

Quantitation of routine chemistry analytes is typically based on one

of two measurement principles – measurement of light (photometry

or spectrophotometry) or measurement of electrochemical potential

(potentiometry). There are many variations of photometry and potentiometry, but all have in common that the signal

the amount of light or electrical voltage

is predictably related to the amount of analyte

in solution.

Accurate test result is our aim

Distinguish between precision and accuracy

•  Describe how calibrator values are assigned

•  Identify the roles of proficiency testing (PT)/external quality assurance (EQA)

and quality control testing programs in ensuring accuracy of test results

1. Laboratory tests must meet precision and accuracy standards.

2. Accuracy, closeness to a true value, depends on a valid calibration process.

3. Calibrator value assignment is linked to a certified reference material,

a recognized reference method or a consensus process that provides

“traceability”.

4. Laboratories use quality control and proficiency testing to monitor the

precision and accuracy of test methods.

Test for analytes in amixtures

Measurement of one substance when it is part of a complex mixture of substances

provides special challenges. A measurement method that works well for determining

the amount of an analyte in a relatively pure form may be completely unsatisfactory

when the analyte is in a mixture of cells, proteins, lipids, carbohydrates and trace

minerals. Methods for the analysis of analytes in complex biologic mixtures require

special approaches to minimize or eliminate interference from other substances. Some

of the approaches frequently used in clinical chemistry such as blanking, rate methods,

pretreatment, reagent specificity and ion-selective electrodes are described in more

detail in the following sections.

where you can  find errors?

preanalytical, analytical and postanalytical errors

1. Patient preparation and proper collection and handling of specimens are

important preanalytical steps to ensure the validity of a test result.

2. Hemolysis, icterus and lipemia (HIL) are three of the most common sources

of interfering substances found in blood serum and plasma samples.

• Hemolyisis refers to color of hemoglobin released from destroyed red blood cells

• Icterus refers to color from bilirubin

• Lipemia refers to turbidity from high lipid concentrations, usually triglycerides

If unrecognized, their presence may cause overestimation or underestimation of

the analyte concentration.

3. Automated instrumentation includes numerous algorithms to detect potential

sources of error and alert the operator.

common  clinical chemistry tests

1. Clinical chemistry tests measure a wide variety of analytes that reflect many

different organ systems and diseases.

2. Some test results are specific indicators for a single organ system or disease;

others are general indicators of a disease or disorder, but do not pinpoint the

specific organ or disease process.

3. Tests are performed for different reasons. Some tests help diagnose a disease,

others monitor the course of the disease progression or effectiveness of

therapy, and still others are used to screen for risk of developing a disease.

Hundreds of compounds, molecules and ions circulate in body fluids. Many of

these can be measured by tests used in clinical chemistry laboratories. These tests

are valuable in the prevention, diagnosis and treatment of disease.

some disases

Diabets millitus

choronic kidney failure

cardiac heart diseases biomarkers

Anaemia