6. Venous blood and capillary blood collection for clinical laboratory investigation - basic procedures, sources of errors. Collection-associated interference. Serum or plasma? Advantages and disadvantages.

Venous blood collection clinical laboratory investigation – basic procedures and sources of errors.

Basic Procedures:

1. Prepare the patient. The most important step is to properly identify the patient. Reassuring the patient. At each step the patient should be told exactly what is going to happen.
2. Assemble supplies.
3. Verify paperwork and tubes.
4. Position in patient. In order to avoid problems with hemo concentration and hemo dilution, the patient should be seated in a supine position for 15 to 20 minutes before the blood is drawn.
5. Apply tourniquet. The tourniquet should be applied enough to restrict venous flow, but not tight enough to occlude arterial flow.
6. Select vein site. Hand and wrist veins should only be used after checking both arms.
7. Cleanse venipuncture site with antiseptic (70 % alcohol).
8. Perform the venipuncture.
9. Release the tourniquet when blood begins to flow. Never withdraw the needle without removing the tourniquet!
10. Fill in the tubes. The proper order of draw is: hemoculture > serum > plasma for hemostasis > ESR and heavy metals > whole blood for hematology tests
11. Gently mix and invert tubes with anticoagulant; Do not shake the tube!
12. Check condition of the patient. Dispose of contaminated material in designated containers
13. Bandage patient arm
14. Identify specimen
15. Chill or warm specimen (if indicated)
16. Eliminate diet restrictions
17. Record collection time.

Errors before venous puncture:

• Misidentification of the patient.
• Patient not properly prepared for testing (e.g. without 12h nutrition starving)
• Change in the position of the body before the procedure

Errors during venous puncture:

• Using needles which are too small (hemolysis)
• The tourniquet should never be left on the arm more than 1 min. After 2 min. local stasis with hemoconcentration and acidosis are observed. This influences the results for albumin, K+, number of Erys, HCT, HGB, WBC, PLT
• Venipuncture in improper vein site (hematoma )
• Tapping on the vein (hemolysis/аctivation of the coagulation factors)
• pumping” with fingers while the tourniquet is applied (local acidosis and hemolysis – K+ and lactate are increased with 20%)

Errors after venous puncture:

• Not loosening the tourniquet after “entering” the vein (stasis) and during the drawing of blood
• Wrong tubes/ wrong anticoagulant
• Wrong order of the evacuated collection tubes (for example first for coagulation )
• Short draw - wrong ratio blood/anticoagulant
• Mislabeling of specimen