Chapter 1 — Introduction to Clinical Biochemistry

What is clinical biochemistry?

The study of chemical aspects of healthy and diseased individuals using laboratory methods for prevention, diagnosis and monitoring of treatment.

How can clinical biochemistry be simply defined?

The chemistry of health and disease.

What are the three phases of laboratory work?

Pre-analytical phase, analytical phase and post-analytical phase.

What is the pre-analytical phase?

The phase including sample collection, transport and preparation before analysis.

What is the analytical phase?

The actual laboratory measurement procedure.

What is the post-analytical phase?

Verification, interpretation and release of laboratory results.

Which laboratory phase causes many errors?

The pre-analytical phase.

Why is the pre-analytical phase important?

Because wrong collection, transport or preparation can produce incorrect results before the analysis even starts.

Which blood samples are used in clinical biochemistry?

Venous, arterial and capillary blood.

Which blood sample is most commonly used?

Venous blood.

When is arterial blood usually used?

Mainly for blood gas analysis.

Why is morning fasting blood collection preferred?

Because some analytes vary during the day and food intake affects glucose and triglycerides.

Which analytes show circadian variation?

Serum iron and cortisol.

Why can glucose decrease after blood collection?

Blood cells continue glycolysis and consume glucose.

Why can potassium increase if plasma stays in contact with cells?

Potassium can leak from blood cells into plasma.

What is hemolysis?

Rupture of erythrocytes with release of their intracellular contents into serum or plasma.

Why is hemolysis a problem?

It can falsely increase analytes found in red blood cells and can interfere photometrically because of hemoglobin color.

Which analytes can increase due to hemolysis?

Potassium, magnesium, LDH and transaminases.

How should serum tubes be handled after blood collection?

Invert once, let clot for 20–30 minutes, then centrifuge.

How are serum and plasma different?

Serum is obtained after clotting and does not contain fibrinogen; plasma is obtained with anticoagulant and contains fibrinogen.

How are anticoagulant tubes mixed?

They are gently inverted 2–3 times.

Why should tubes be closed during centrifugation?

To prevent aerosols, infection risk and sample evaporation.

What is EDTA used for?

Mainly hematology tests such as complete blood count.

How does EDTA prevent coagulation?

It chelates calcium ions.

What is citrate used for?

Coagulation tests and erythrocyte sedimentation rate.

How does citrate prevent coagulation?

It binds calcium in a soluble non-ionized form.

What is heparin used for?

Often for blood gas analysis and some plasma biochemical tests.

How does heparin prevent coagulation?

It inhibits the conversion of prothrombin to thrombin.

What is sodium fluoride used for?

It inhibits glycolysis and stabilizes glucose.

Which enzyme does fluoride inhibit in glycolysis?

Enolase.

Why is fluoride not used for all biochemical tests?

It can interfere with enzyme assays and some other biochemical parameters.

What is first morning urine used for?

Complete urinalysis, including chemical test strip analysis and sediment microscopy.

Why is first morning urine useful?

It is the most concentrated urine sample and is best for sediment examination.

How quickly should complete urinalysis be performed?

Immediately, or within 2 hours.

How is 24-hour urine collected?

The first morning urine is discarded, then all urine is collected until and including the first morning urine of the next day.

Why is 24-hour urine stored at 4°C?

To reduce bacterial growth and chemical degradation.

What is centrifugation?

A procedure that separates heavier from lighter components using centrifugal force.

What is RCF?

Relative centrifugal force, expressed as multiples of g.

What is a supernatant?

The clear liquid above a precipitate after centrifugation.

What is a precipitate?

The solid material collected at the bottom after centrifugation.

Where is centrifugation used in the HDL protocol?

To separate precipitated LDL/VLDL/chylomicrons from HDL-containing supernatant.

What is lipemic serum?

Cloudy or milky serum caused mainly by high triglycerides.

Why does lipemia interfere with tests?

It causes light scattering and sample non-homogeneity.

What is icteric serum?

Yellow serum caused by high bilirubin concentration.

Why does icterus interfere with tests?

Bilirubin can cause optical interference in visible photometric methods.

What is a sample blank?

A correction measurement used when the sample itself has color or turbidity.

What is internal quality control?

Daily testing of control materials with known target values inside the laboratory.

What is external quality control?

Comparison of results with other laboratories using unknown control samples from an external organization.

What does internal QC mainly check?

Daily precision and routine analytical performance.

What does external QC mainly check?

Accuracy and comparability between laboratories.

What is reagent grade water type 1 used for?

Analyses requiring maximum accuracy, such as trace elements, enzymes and electrolytes.

What is reagent grade water type 3 used for?

Washing laboratory glassware.

Why must pipettors be calibrated?

Because wrong pipetting volumes cause wrong analytical results.

What is phlebotomy?

The process of collecting blood for analysis.

What is the most common venipuncture site?

The medial cubital vein in the antecubital fossa.

Why should the patient sit before venipuncture?

Body position affects some analyte concentrations.

Why should blood not be drawn above an active infusion?

The sample can be contaminated or diluted by the infusion fluid.

Why should disinfectant dry before venipuncture?

Remaining disinfectant can cause hemolysis.

How long should a tourniquet usually stay applied?

Less than one minute if possible.

Why should fist pumping be avoided?

It can increase potassium, phosphate and lactate.

Why must anticoagulant tubes be filled to the mark?

To keep the correct blood-to-anticoagulant ratio.

What is capillary blood collection?

Open blood sampling by skin puncture with a lancet.

Where is capillary blood collected from?

Fingertip, heel in infants or earlobe.

Why is the first drop of capillary blood wiped away?

It may contain tissue fluid and contaminants.

Where should contaminated needles be disposed?

In a rigid single-use plastic sharps container.

Why must mouth pipetting not be used?

It creates infection and chemical exposure risk.

When should gloves be worn?

Whenever exposure to blood or body fluids is expected.