pre analytical phase of laboratory phases ,steps and biochemistry how to run a test

1. Laboratory Medicine

2. Pre-analytical phase
Procedure of blood collection –
•A blood sample is taken by a
phlebotomy in a laboratory
•Blood samples are taken in the arm,
hand and finger(in some cases)
•Collection takes place from the
median cubital vein

3. The first step to the collection is to:
• Ask the patient to state and spell his/her
name
• Give you his/her birth date
• Check these against the requisition
• Put the gloves

4. The second step
• Identify the Vein
• Put a tourniquet on patients arm
• Clean the vein area with alcohol swab and allow
to air dry for 30 seconds
• Insert the needle at a 15 to 30-degree angle
• If properly inserted, blood should flash into
the tube or syringe

5. • Remove the proper volume of blood
• Release the tourniquet within one minute
• Remove the needle from the patient's arm
• Press down on the vessel with cotton

6. The third step
• Dispose of contaminated materials and needles in the
hospital approved containers
• Shake the tubes 3-4 times
• Wright the name of patient on the tubes
• Stand the tubes 5 minutes before centrifuging
• Put the tubes in the centrifuge
• Deliver blood specimens to the laboratory

8. Effects of pre-analytical phase
• Age
• Sex
• Diet
• Drugs
• Exercise
• Diagnostic procedures(endoscopy)
• Pregnancy
• Timing of collection
• Hemolysis, lipemia, jaundice
• anti-coagulants

9. Hemolysis
May easily occur during blood sampling:
• very intense aspiration of blood
• too hard mixing of sample
• too long time putting a tourniquet
• transferring blood from the syringe to the
tube with needle
• cooling down the sample on <0°C

10. potassium measurement will be highly
affected by hemolysis.

11. lipemia occurs when patient don’t fast 12
ours before sampling

12. Hemolysis, lipemia, jaundice

13. Anti-coagulants
when taking blood gases
and electrolytes
• Heparin binds all positive ions in blood, especially
calcium ions
• Dilution with liquid heparin cozies decreased results of
electrolytes
• Therefore dry heparin is recommended
That’s why:
• Exclusive use of preheparinized syringes are
recommended for electrolyte measurements on a
blood gas analyzer

14. Sampling from catheters
should avoid
• dilution or contamination by flush solution(0.9
% NaCl)
• it is important to remove an adequate amount
of fluid (also called the discard volume,
consisting of flush solution and blood) before
sampling to avoid interference and dilution
from/by the flush solution on the electrolyte,
pH, and blood gas parameters.