Vacuum blood sampling technique

Vacuum systems: equipment and purpose

A standard vacuum blood collection system consists of three components:

Double-edged needle for venipuncture.
Holder (adapter) for fixing the needle.
Vacuum tube with reagent.

All components of the system are intended for one-time use only.

The principle of operation of the system: under the influence of a vacuum, blood is drawn into a test tube with a reagent and immediately mixed with it. A certain amount of reagent and the volume of blood required for the study provide the exact ratio of components for the study.

Factor No. 7. I worked hard and got nervous

Physical activity, especially intense or unusual for the patient, can increase the CBC indicators, namely the number of red blood cells, white blood cells and hematocrit. Psycho-emotional stress will also affect the number of leukocytes. In this case, chronic severe stress is considered as a basic pathological condition, and acute stress is taken into account, for example, with sensitivity to service in municipal institutions.

How it affects: For biological variation, the most sensitive indicator is leukocytes. Physical overexertion in combination with deviations in the time of sampling can change the number of leukocytes by ± 4 × 109/l.

Needles

The wall of the blood collection needle is ultra-thin, which increases its internal lumen. The outer and inner surface of the needle wall is coated with silicone to reduce trauma to the patient and improve free blood flow. The V-shaped laser sharpening of the cut facilitates painless, smooth entry of the needle into the vein through the skin.

On the tip side for piercing the test tube, the needle is equipped with a thread and a protective rubber membrane. The needles are sealed in two plastic cases (caps) and sealed with a label to prevent their reuse. The color coding of the caps helps in choosing the needle diameter.

Factor No. 8. “Casual” smoking

A mandatory point that must be taken into account by the clinician is smoking. The condition where the patient is a chronic smoker is regarded as the basic condition. If a person was forced to quit smoking and this fact is unknown to the attending physician, then the number of erythrocytes, platelets and hematocrit are subject to changes in the CBC, and the changes can be of a different nature. Particular attention should be paid to adolescents - a group of patients who smoke rarely and irregularly.

How it affects: “Sudden” smoking before taking a blood test can overestimate the number of red blood cells by 10%.

Preparation for the procedure

Check that all necessary equipment is available.
Check the expiration date and integrity of the vacuum system packaging.
Check the expiration date and tightness of antiseptic wipes.
Take the needle by the long colored cap in one hand, and with the other hand remove the short colored cap from the side of the rubber membrane.
Insert the freed end of the needle with the rubber membrane into the holder and screw it until it stops.
Place the needle and holder on the tray.
Prepare the necessary test tubes in sufficient quantity.
Wear sterile gloves.

Factor No. 6. “Easy”

It is recommended that blood collection be done early in the morning after a 12-hour fast and no changes in diet for 24 hours. The patient should go to bed at the usual time the day before and get up no later than an hour before blood collection (baseline).

How it affects: Important for hemoglobin levels. Sample turbidity, even slight, distorts photometric data. Hemoglobin is likely to be elevated, which will affect the control of anemic patients. The MCHC indicator can serve as a control over the correctness of hemoglobin measurement.

Carrying out manipulation

Ask the patient to make room for the upcoming venipuncture (most often the elbow, possibly the forearm, the back of the hand).
Place an oilcloth pillow under the venipuncture site.
Apply a tourniquet 7-10 cm above the venipuncture site on top of clothing or a diaper. The tourniquet is applied so that the pulsation of the nearby artery is maintained.
Ask the patient to make a fist.
Inspect and palpate the vein for venipuncture.
Treat the venipuncture site with antiseptic wipes.
Hold the vacuum system in one hand and remove the protective cap from the needle with the other hand.
With your free hand, stretch the skin below the venipuncture site at a distance of 4-5 cm to secure the vein.
Puncture the vein at an angle of 10-15º, insert the needle along the vein no more than 1/2 of the length.
Take the test tube and insert it into the holder until it stops.
Once the blood begins to flow into the tube, remove or loosen the tourniquet.
Ask the patient to unclench his fist.
Draw the required amount of blood into a test tube.
Remove the tube from the holder when blood stops flowing into it.
Carefully invert the tube several times to mix the blood with the filler. Do not shake the test tube!
Place the test tube in a rack.
If necessary, connect the next test tube to the system and repeat all steps.
Draw the required amount of blood into all tubes.
Apply a sterile napkin with an antiseptic to the venipuncture site and remove the needle.
Ask the patient to press down on the tissue with his free hand.
Place the needle in a sharps container - Class B waste.
Place the holder in another container for collecting Class B waste.
Apply a pressure bandage or adhesive bandage over the napkin.
Inquire about the patient’s well-being and make sure everything is okay.
Label the tubes containing the collected blood samples with the patient's last name and initials.
Place used consumables in Class A and B waste containers.
Make the necessary notes in medical documentation on paper and electronic media.
Send the collected material with accompanying documents to the laboratory.

Factor #1: Finger or Vein?

Comparisons of two CBCs collected under different conditions/from different sources (from a vein and from a finger) should be done with caution. Indicators of capillary and venous blood may differ.

The ulnar vein is the optimal place for blood collection for general analysis, taking into account the requirements of standardization and the exclusion of preanalytical influences. However, the choice of material for testing the CBC remains with the laboratory. The only way to reduce the occurrence of interpretation errors associated with the selection of study material is to adhere to a uniform preanalytical methodological framework offered by the laboratory.

When taking blood from a finger, a number of features are possible that are difficult to standardize: cold, cyanotic, swollen fingers, the need to dilute the blood being tested, and others. Tissue fluid, which inevitably ends up in capillary blood, contains thromboplastin, which promotes the formation of microclots.

If the laboratory works with venous blood to study the cellular composition, then it is recommended to take capillary blood in the following cases:
the need for daily monitoring of blood counts, for example in cancer patients undergoing chemotherapy;
for burns of a large surface area of the body;
in the presence of hard-to-reach veins;
with severe obesity;
with an established tendency to venous thrombosis;
in newborns.

How it affects: There may be a significant scatter in the results obtained, which are leveled out in repeated samples. The number of erythrocytes, hematocrit, qualitative composition of the leukocyte formula and ESR in an analysis performed under different conditions in the same patient may change regardless of the course of the underlying pathological condition. Capillary blood contains a higher content of leukocytes and a lower content of platelets compared to venous blood.

Basic blood test indicators

Hemoglobin is a protein found in red blood cells. Its main function is to provide the body with oxygen. Both increased and decreased hemoglobin levels may indicate serious disorders: problems with the gastrointestinal tract, iron deficiency anemia, heart failure, etc.

Erythrocytes are red blood cells. Their excess can lead to thickening of the blood and the appearance of frequent headaches, dizziness, and nosebleeds. A low red blood cell count often leads to fatigue and tinnitus.

Reticulocytes are the precursors of red blood cells that are formed in the bone marrow. If their content is reduced, this may indicate a disruption in the formation of red blood cells. An increased content of reticulocytes may indicate the presence of blood loss.

Platelets are blood platelets responsible for blood clotting. A deviation of the platelet level from the norm may indicate the presence of serious diseases, such as tuberculosis, cancer of the liver and kidneys, bone marrow lesions, and leukemia.

ESR is the erythrocyte sedimentation rate. It may indirectly indicate the presence of an inflammatory process in the body.

Leukocytes are white blood cells. Their deficiency may indicate, among other things, the presence of an infectious disease.

Neutrophils are one of the types of leukocytes. Help the body fight bacteria. Their reduced content may indicate the presence of a severe infection in the body. If other blood parameters are normal, an increase in the level of neutrophils does not indicate the presence of serious problems in the body.

Lymphocytes are cells of the immune system. An increase in the level of white blood cells can be observed in children during the period of recovery from infectious diseases. A decrease in the content of lymphocytes in the blood is observed at the onset of the disease.

Monocytes are a type of white blood cell. Their function is to cleanse the body and support the immune system. An increase in their content may indicate an inflammatory or oncological disease.

Eosinophils are white blood cells responsible for destroying foreign protein in the body. They are elevated in allergic diseases.

Basophils are white blood cells, an increase in the content of which may indicate the presence of an inflammatory process or a foreign body in the body, as well as inflammation in the digestive organs and disruption of the thyroid gland.

Plasmocytes are cells that are part of the immune system and are responsible for the production of immunoglobulins (antibodies). They may appear in the blood during infectious diseases such as chickenpox, rubella, and measles.

Factor No. 9. Drugs/medicines

Medicines and their metabolites can change OAC parameters due to a physicochemical effect on the procedure or due to their interaction with the device and reagents.

If the patient takes medications, especially in large dosages, such as antipyretics, analgesics, antibiotics, antispasmodics, it is necessary to take into account the effect of their metabolites on blood pH. The more medications a patient takes immediately before donating blood, the higher the likelihood of distorting the result. In addition, the presence of active metabolites significantly reduces the standardized time available for analysis. For UAC, the optimal execution time is considered to be 2 hours, within which the material remains as stable as possible. For CBC calculated on a hematology analyzer, this time is 6 hours. For OAC, if the patient has taken a large amount of medications, the time can be reduced to 30 minutes for any type of study.

Life-saving medications should be taken as usual! Their presence in the blood is the basic state from which dynamics are assessed.

How it affects: When a blood test with drug metabolites is carried out later than the established time interval, the volume of leukocytes changes, the volume of erythrocytes increases, which leads to errors in the morphological differentiation of leukocytes and calculated erythrocyte indices.

The platelet count when taking antiplatelet agents (NSAIDs, acetylsalicylic acid) may be underestimated by the analyzer. Falsely elevated MCV index can occur with hyperglycemia and ketoacidosis due to plasma hyperosmolarity.

If there is an excess of medicinal metabolites in the blood, the morphological characteristics of neutrophils and monocytes will change, the volumes will decrease and the form of other elements of the blood test will change. In practically healthy people, changing the basic parameters of cells will not cause significant changes in the count. The state of pathological elements in severe diseases cannot be standardized; the only requirement is to minimize the time before starting the analysis.

Doctors will find it useful

If you see that “the laboratory is lying,” check: where the material was taken from, by whom and under what conditions. Comparison of indicators performed under the same conditions (laboratory, personnel, methodology) is considered correct.

Find out from the patient what happened before the analysis: physical activity, stress, taking medications, smoking. Warn patients that before the test, if there is no urgent need, it is better to postpone taking medications. It is ideal to withhold medication for 12 hours - this is the standard half-life for most medications. Warn the patient to maintain a state of psycho-emotional and physical rest before the blood collection procedure.

And only by eliminating factors that could influence the preanalytical stage can the obtained changes be compared with the patient’s clinical indicators in order to provide him with quality medical care.