Pre-analytical quality control
Introduction
Hello, in this second class of the Hematology course, we are going to check some aspects of the Pre-analytical quality control. This Is a very Important stage in every laboratory, because all the factors that are Involved can affect and/or destroy components, properties Important to be analyzed, thus Invalidating the final report. Also, the patient management Is very Important, because they expect to be treated with respect, to have the necessary tests performed, to receive precise instructions prior to undergoing tests, to get reliable Results that reflect their clinical condition.
An Important procedure to begin with Is the blood collection, with all the technical aspects and precautions that must be considered, as well as the devices used to vein puncture, a couple of videos showing lab professionals drawing blood with these devices.
Then, some Information about anticoagulants Is going to be reviewed, since most of the hematology lab work needs the preservation of blood cells.
So, let’s get started.
Content development
Pre-analytical phase: It includes all the steps from the time the laboratory test is requested until it is executed; it is a very broad phase that includes processes both outside and inside the clinical laboratory.
The most common errors are present in the request form for the test and during the in vitro examinations.
Must be performed in agreement with the requesting physicians.
Special conditions of the patient are needed for the performance of the study. Stages of the pre-analytical phase:
- Analytical request
- Patient preparation
- Identification and collection of samples
- Handling, transport, and storage
- Reception, preparation, and distribution
- Rejection of invalid samples
- Referral to external laboratories
Specifications of the test request form:
- Complete patient identification
- Requesting Physician
- Tests requested
- Type of biological material
- Date and if necessary, time
- Priority (Emergency or routine)
- Clinical information needed (medication or drug intake, antimicrobial therapy).
- Presumptive diagnosis.
Errors in the conditions of blood collection and clinical specimen collection: These are the most frequent errors that occur in the pre-analytical phase.
The strategy to solve these errors, which mainly occur outside the clinical laboratory, is training. Training phlebotomists through courses or workshops that provide information on the conditions under which blood draws should be performed and how to question the patient about the regular intake of medications, fasting time, etc. Personnel outside the clinical laboratory should be aware of the importance of the correct performance of this phase.
Blood collection:
Since the cell count is affected by the state of the blood circulation, the conditions under which the blood samples are taken should always be the same.
Blood should be drawn at the same time of day and after an 8-hour fasting period, as both nutritional status and circadian rhythm can affect the results.
Ethical Aspects:
The person should be informed that a sample is planned to be obtained, the type of sample, the tests to be performed on the sample, and the results expected and obtained.
It is important to obtain the consent of this person.
The type of consent can be verbal or written, according to the objectives.
In the case that the intention is to know the health status, it can be verbal.
If it is for research purposes, the consent must be stated in writing, indicating the procedure and the repercussions it may have for your person (especially if it is a sample for DNA analysis or HIV identification), and the acceptance form must have a consent signature.
Sites of venous blood collection:
Materials needed:
Procedure:
Use of tourniquet for vein identification. The tourniquet should be in place for a maximum of 1 minute during the entire sample collection process.
Once the vein has been selected, clean the area with 70% alcohol using a swab and Inside Out circular or top to bottom movements, always taking care not to pass the same side of the swab more than once. Once decontamination has been performed, the puncture area should not be touched again once the asepsis of the puncture site has been performed.
An elastic band is placed around the upper arm in order to apply pressure to the area. This causes the vein to fill with blood.
A needle is inserted into the vein WITH THE BEVEL UP. The blood is collected in a vacuumed vial or tube attached to the needle. The elastic band is removed from the arm.
The needle is removed and the site is covered with a new swab to stop the bleeding and the patient is asked to bend the arm or just to apply some pressure in the punction site.
A capillary blood sample may be taken when large amounts of blood are not required.
If circulation is very poor, blood flow can be increased by warming the limb by immersing it in warm water.
The area to be punctured is cleaned with 70% alcohol without exerting pressure, after which the area is punctured firmly but gently with a sterile disposable lancet.
The first drop of blood is discarded for possible contamination, and a sample can be obtained with a capillary. Care should be taken not to exert too much pressure on the tissue from which the blood is obtained because the composition of the blood may be modified.
Extraction systems:
Butterfly
It is a very comfortable system for the blood collector as well as for the patient. The set consists of a butterfly blood collection needle attached to a flexible, transparent tube with a Luer connector, to which a blood collection system (e.g. vacutainer type) is attached.
You can watch the following video where a professional uses the butterfly device: https://ugtomx-my.sharepoint.com/:v:/g/personal/c_albabetancourt_ugto_mx/EZ7XCbb2_xZEmrRshp6yaqEBCzeZyTlmbSQMmv3mUbaBmA?e=aQMPzG.
Vacuum system
It is widely used because its use is simple and practical. The vacuum tube is hooked into an adapter which is attached to the needle. The vacuum fills the tubes by themselves. The use of vacuum systems is not recommended for babies and elderly people because of the fragility of their blood vessels. The advantage of this system Is that a several blood samples can be obtained with just one puncture.
You can watch the following video where a professional uses the multi sample needle: https://ugtomx-my.sharepoint.com/:v:/g/personal/c_albabetancourt_ugto_mx/ETBeLSAK1DFIpiGlG60KDyEBwNKlRmEIJ1ptABSFOf-cGg?e=VAlZAM
Syringe
Most common and used technique. Secure the needle and loosen the plunger. Immediately empty the blood into the appropriate collection tube. With this device the phlebotomist can easily visualize If the vein has been correctly punctured.
Possible complications:
- From the patient:
- Excessive movement (especially in children)
- Excessive bleeding at the puncture site (e.g., patients taking anticoagulants).
- Infections (at the puncture site)
- Hematoma
- Fainting or Dizziness
From the phlebotomist:
- Change the position of the needle (it comes out of the vein)
- Inserting the needle at an improper angle or inserting it too deeply.
- Needle lumen sticks to the vein wall (solution: turn the needle slightly)
- Vein collapsed
- Multiple punctures to locate a vein
Accessing an artery
- After the blood collection, It Is also really Important to discard all the material In proper containers.
- Special attention must be paid to the activation of needles, as the previous videos have already mentioned.
Please watch the following this video where some health care professional talk about their experience with accidental needle puncture: https://ugtomx-my.sharepoint.com/:v:/g/personal/c_albabetancourt_ugto_mx/EUDvVzvpCyxNmclmQ_5vaXcBq1hKhWJinxlC0J3fyh3t0g?e=em3j8Q
Anticoagulants
Unclotted blood is required for all hematological work and for many biological analyses.
BASIC CHARACTERISTICS OF THE MOST COMMONLY USED ANTICOAGULANTS IN HEMATOLOGY
- Do not alter the size of red blood cells.
- Do not produce hemolysis.
- Avoid platelet aggregation as much as possible.
- Do not alter the morphology of leukocytes.
Four are the most frequently used anticoagulants:
Oxalate mixture
Citrates EDTA
Heparin
Anticoagulants can be used in solid or liquid form.
SODIUM OXALATE (Liquid)
Frequently used as an anticoagulant in biochemistry.
Can be used for the determination of hemoglobin, erythrocyte and leukocyte count and hematocrit.
It is not used in transfusions because it is toxic.
Blood smears should be done immediately because after a few minutes, oxalate causes nuclear degeneration in leukocytes and plasmolysis in red blood cells.
TRISODIUM CITRATE (Liquid)
3.8% sodium citrate, precipitates calcium.
Used to obtain citrated plasma.
Used in blood coagulation and platelet function tests.
Preservation of the sample for 1 hour.
EDTA (sodium, potassium salt of ethylene diamine tetra acetic acid)
Chelates blood Ca2+. Used for blood cell morphology studies.
Does not alter erythrocyte sedimentation rate.
Preserves samples for up to 24 hours or for 48 hours at 4°C.
The recommended concentration of EDTA is 1.5 mg/mL of blood.
A higher quantity of anticoagulant can produce cellular retraction, with a decrease in hematocrit, and an increase in the mean hemoglobin concentration.
An excess of blood in relation to the anticoagulant leads to the formation of microaggregates that can alter the results.
Heparin
Natural anticoagulant
Interferes with the conversion of prothrombin to thrombin.
Used for plasma collection in blood chemistry, hormone profiling and blood gas analysis.
Preserves samples for 8 to 10 hours.
Minimizes hemolysis but is not suitable for blood smears as it produces a diffuse blue coloration.
It is also not suitable for leukocyte or platelet counts as it produces cellular aggregation.
Conclusion
The pre analytical phase comprises everything necessary prior to analyzing the blood sample.
It Is a very important phase because any error could Invalidate the whole laboratory process and the results.
The blood sample collection Is one of the most Important part of this phase.