What is pre-analysis?

Pre-analysis consists of everything that is done before the actual analysis of the blood sample. The time of day, patient's position during the venipuncture, the kind of the venipuncture, time between blood drawing and testing, storage and transportation of the blood, etc. can all influence the outcome of a blood test.

Venipuncture

Blood films are usually prepared using blood drawn by venipuncture and anticoagulated with EDTA. Mistakes that lead to artifactual results can occur when the blood is being drawn (pre-analytic error). For example, vein compression should only be maintained during the venipuncture. No compression should occur during the actual venipuncture. If compressed too long (> 2 mins.), the plasma:cell ratio is modified. Injury to the vessel wall during the venipuncture also leads to alteration of blood composition. A venipuncture proximal to a sight of infusion cannot be analyzed because the blood has been diluted by the infusion solution (values too low) on the one hand, and by substances in the infusion (e.g. Heparin) that can change the qualities of the blood on the other. The blood tube must be well-mixed immediately after the venipuncture by repeatedly inverting the tube. After completing the venipuncture, all tubes are labeled with the patient's personal data, never before.

If a venipuncture is difficult or even impossible (babies, children, bad veins), capillary blood drawing is an alternative. For the extraction of capillary blood, the skin is pricked with a sterile lancet. Places for puncture include the heel, the big toes and the fingertips III-V. The prick must be at least 1.5 mm deep. Blood withdrawal is increased with gentle pressure. The first drop of blood is discarded due to the proportion of tissue fluid. Blood is then collected with pipettes or capillaries, in which the latter ideally already contains EDTA.

Storage and transportation

After the venipuncture, further alterations of the blood can occur (artifacts). In order to limit these influences, the blood should be kept sterile and, for blood films, at room temperature (avoid heat) and should be processed within two hours.

The following is a list of different hematological investigations and their tolerance time. The tolerance time is the amount of time which may elapse between venipuncture and testing that will not influence the investigation results. These tolerance times are only valid if the specified storage temperatures are adhered to.

For the these investigations,  the blood should be stored at 4°C:			For the these investigations,  the blood should be stored at room temperature:
Investigation	Tolerance time		Investigation	Tolerance time
Hematocrit	24h		Blood film for differential blood count	2h
Hemoglobin	48h		Erythrocyte sedimentation rate	2h
Erythrocyte count	12h		Platelet count	12h
Leukocyte count	24h
Reticulocyte film	24h