Highlights on the monitoring and control of preanalytical variables By Mohamed Osama Ali Assistant lecturer of clinical pathology Faculty of medicine Suez canal university

Types of preanalytical variables Test selection. Patient preparation. Patient identification. Specimen collection. Specimen transport.

A) Appropriate test selection Clinical practice committees: limitation of kind and volume of requests available for emergency. Guidelines for appropriate use of laboratory tests. Careful monitoring of appropriateness of test requests.

B) Patient preparation Laboratory tests are affected by many factors (food, alcohol, drugs, smoking, exercise, stress, and posture) The laboratory must define the instructions and procedures for patient preparation and specimen acquisition. These should be included in hospital procedure manuals Instructions should be transmitted to the patient both oral and written. Compliance with these instructions can be monitored directly by the laboratory phlebotomist.

C) Patient and specimen identification The highest frequency of errors occurs with the use of handwritten labels and request forms. These can be eliminated by: – The phlebotomist should confirm patient’s identifiers (name, medical record number, date of birth, room location or address) – The integration of barcode technology.

D) Specimen collection Posture. Site. Timing. Tourniquet. Syringes. Anticoagulant (additives) Hemolysis.

1- posture: The patient should be comfortably seated or supine for 20 minutes. The patient arm should be extended in a straight line from the shoulder to the wrist. 2- collection site. The median cubital vein is the preferred site. Veins on the hand or at ankle be used. Avoid the arm with: Extensive scarring or hematoma. Containing I.V. access for I.V. infusion. On the side of mastectomy.

Preparation of the collection site: The area around the intended collection site should be cleaned with alcohol swab. The skin should be allowed to dry in air. 3- timing of sampling: Timing is important for analytes that undergo diurnal variation and for monitoring drug therapy.

4- venous occlusion (tourniquet): cm above the collection site. Shouldn’t be left in place for more than 1 min. Should be released with starting of blood flow into the syringe. Prolonged stasis causes hemoconcentration. Avoid pumping of the fist before venipuncture. 5- syringes: Vigorous suction by the syringe or forceful transfer from the needle to the tube may cause hemolysis. After blood collection needle is removed and blood is transferred to the collection tubes by gentle ejection. Tubes should be capped and if they contain anticoagulant they should be gently mixed (10 inversions at least)

6- Anticoagulants: Heparin. EDTA. Citrate. Oxalate. 7- hemolysis: Affects analytes that are present at higher concentrations in erythrocytes than in plasma (ACP, LD, AST, K, Mg, P) Hemolysis may also affect unblanked analytical methods.

E) Specimen transport Temperature Light

F) Specimen separation and transport These are under the control of the laboratory. The main variables are: Centrifuges. Containers. Personnel.

conclusion Preanalytical variables can dramatically affect the results of laboratory tests. Paying close attention to control the preanalytical variables will help to ensure accurate test results in clinical laboratory.