Clinical specimen collection, Lecture notes of Clinical chemistry

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Specimen Collection and

Handling for Biochemical

Analysis

Zakayo Thaimuta

Human Pathology

School of Medicine

Why are laboratory tests ordered

• Diagnosis
• Monitor progression of disease
• Monitor effectiveness of treatment
• Screening population for diseases
• To identify complications of treatment
• For predicting survivability, employability - To check the accuracy of an unexpected data - To conduct research - To prevent malpractice - For educating residents - To assess nutritional status and health of an health individual - Responding to total 9/19/2014 2

The Test Highly Specific marker: Troponin I. It is a marker of Myocardial infarction (Heart Attack) Found predominately in Cardiac Tissue Released into the blood stream following cell death Non specific marker: low blood pH (acidosis) Very important to know but can be caused by a hosts of events Drugs Respiratory problems Renal problems

Biological Specimens

• Blood
• Urine
• Cerebrospinal Fluid
• Amniotic Fluid
• Duodenal Aspirate
• Gastric Juice
• Gall stone
• Kidney Stone Comprise the majority of all specimens analyzed

Blood Composition Plasma Plasma is fluid component of blood. Comprises ~55% of total volume of whole blood. Contains proteins, sugars, vitamins,minerals, lipids, lipoproteins and clotting factors. 95% of plasma is water Red Blood cells (RBC) Whole Blood Whole Blood after centrifugation Note: clotting has been prevented White Blood cells (WBC) & Platelets Cellular Components

Blood Composition Serum Plasma is fluid component of blood. Comprises ~55% of total volume of whole blood. Contains proteins, sugars, vitamins,minerals, lipids, lipoproteins No clotting factors 95% of plasma is water Blood Clot

• comprised of clotting factors (Fibrin,platets etc)
• RBCs Whole Blood Whole Blood after clotting and centrifugation If blood is collected and allowed to stand it will clot. Formation of an insoluble fibrin clot. If blood is then centrifuged the fluid portion is known as SERUM

Blood Analysis

• Testing can be done on whole blood, serum or plasma. Choice depends on a number of factors
• Analyte to be measured
  • Most hematology tests requires whole blood
• Instrumentation used for analysis
  • Most automated instruments are not set up for whole blood analysis

• The way the test was developed.
  • Tests are often only validated on either plasma or serum
• Turn around time
  • Analysis of whole blood is the quickest. No waiting for clot or spinning
  • Plasma requires centrifugation prior to analysis
  • With serum, the blood must clot then you have to centrifuge Blood Analysis

Blood specimen

• Serum is a specimen of choice for

electrophoresis.

• Plasma forms fibrin clots when it is

stored. This can pose interpretation

difficulties on electrophoretic patterns

• Serum is useful in analyte which have

carrier proteins. Examples of carrier

proteins are thyroid binding globulin,

cortisol binding globulin, albumin

Blood specimen

• For example, heparin affect binding of

T3 and T4 to their carrier protein (TBG)

thus producing higher free

concentration of the free component

Heparin

• Causes least interference with the tests
• Contains antithrombin which prevents

transformation of prothrombin to

thrombin thus formation of fibrin from

fibrinogen

• Demerits include:
  • High cost and temporary action
  • Inhibition of acid phosphatase activity
  • Inactivation of hydroxybutyrate DH and LDH 9/19/2014 16

EDTA

• Useful in hematological examinations

because it preserves the cellular

components of blood

• Inhibits activities of: creatine kinase,

leucine aminopeptidase, alkaline

phosphatase

• Chelating agent for divalent cations e.g.

calcium, magnesium

Blood Analysis in the Chemistry

• Since most tests in the chemistry lab involve analytes that are dissolved in the fluid portion of blood, serum or plasma are the specimens of choice.
• Important exceptions include
  • Hemoglobin, Red blood cell (RBC) Folate
  • Blood gases
• Protein electrophoresis was developed based on the analysis of serum. Not done on plasma because of the presence of the protein fibrinogen which distorts the electrophoretic pattern.
• Many tests can use either serum or plasma

Collection Tubes

• The most widely used tubes for blood collection are evacuated tubes (Vacutainers) - Negative pressure facilitates collection - Easy to use - Sterile - Universally used colour-coded rubber stoppers to denote tube type. - Tubes can contain various anticoagulants for the collection of whole blood or plasma. - Tubes can have additives for specific tests (glucose, metals)