Blood and bone marrow examinations constitute the major means of determining blood disorders like anemia, leukemia, porphyrias disorders, abnormal bleeding and clotting and inflammation, infection and inherited disorders of red blood cells, white blood cells, and platelets. Specimens are obtained through capillary skin punctures of the fingers, toes, heels or dried blood samples, arterial or venous sampling, or bone marrow aspiration.
Specimen collection
Most hematology tests use liquid ethylenediaminetetraacetic acid (EDTA) as an anticoagulant. Tubes with anticoagulants should be gently but completely inverted end over end 7 to 10 times after collection. This action ensures complete mixing of anticoagulants with blood to prevent clot formation. Even slightly clotted blood invalidates the test, and the sample must be redrawn. For plasma coagulator studies, such as prothrombin time (PT) and partial thromboplastin time (PTT), the tube must be allowed to fill to its capacity or an improper blood-to-anticoagulant ratio will invalidate coagulator results. Invert 7 to 10 times to prevent clotting.
Skin Puncture
Capillary blood is preferred for a peripheral blood smear and can also be used for other hematology studies.
- Collection Procedure
Observe standard Operational Guidelines and Precautions
Obtain capillary blood from fingertips or earlobes (adults) or from the great toe or heel (infants).
Disinfect puncture site, dry the site, and puncture skin with sterile disposable lancet no deeper than 2 mm.
Wipe away the initial drop of blood.
Collect subsequent drops in a microtube or prepare a smear directly from a drop of blood.
- Patient Intervention Procedure
Instruct patient about purpose and procedure of test.
Inform patient that mild discomfort may be felt when the needle is inserted.
Ensure that there is no bleeding from the site.
Apply small dressing or adhesive strip to cover.
Slightly pressure the site if it continues to bleed.
Evaluate patient's medication history for anticoagulation or acetylsalicylic acid (ASA)-type drug ingestion.
Venipuncture
Procurement of larger quantities of blood for testing is done through Venipuncture. The antecubital veins are the veins of choice because of ease of access and the blood values remain constant no matter which venipuncture site is selected, so long as it is venous and not arterial blood.
- Collection Procedure
Use a tourniquet on the upper arm to produce venous congestion.
Tell patient to close the fist in the designated arm and select an accessible vein.
Disinfect puncture site, dry the site,
Puncture the vein according to accepted technique.
Usually, for an adult, anything smaller than a 21-gauge needle might make blood withdrawal more difficult.
Blood will fill vacuum tubes automatically because of negative pressure within the collection tube.
Remove the tourniquet before removing the needle from the puncture site.
Remove needle. Apply pressure and put a sterile dressing strip on the site.
Note that even slightly clotted blood invalidates the test and the sample must be redrawn.
- Patient Intervention Procedure
Instruct patient about purpose and procedure of test.
Inform patient that mild discomfort may be felt when the needle is inserted.
Place the arm in a fully extended position with palmar surface facing upwards.
Ensure that there is no bleeding from the site.
Apply small dressing or adhesive strip to cover.
Slightly pressure the site if it continues to bleed.
Sometimes patient may become dizzy, faint, or nauseated during the venipuncture.
The phlebotomist must be constantly aware of the patient's condition.
If a patient feels faint, immediately remove the tourniquet and terminate the procedure.
If the patient is sitting, lower the head between the legs and instruct the patient to breathe deeply.
A cool, wet towel may be applied to the forehead and back of the neck, Call the physician immediately when you feel something strange or if the patient faints.
Bone Marrow Aspiration
Bone marrow is located within cancellous bone and long bone cavities. It consists of a pattern of vessels and nerves, differentiated and undifferentiated hematopoietic cells, reticuloendothelial cells, and fatty tissue. All of these are encased by endosteum, the membrane lining the bone marrow cavity. After proliferation and maturation have occurred in the marrow, blood cells gain entrance to the blood through or between the endothelial cells of the sinus wall.
A bone marrow specimen is obtained through aspiration or biopsy or needle biopsy aspiration. A bone marrow examination is important in the evaluation of a number of hematologic disorders and infectious diseases. The presence or suspicion of a blood disorder is not always an indication for bone marrow studies. A decision to employ this procedure is made on an individual basis.
Sometimes, the aspirate does not contain hematopoietic cells. This “dry tap” occurs when hematopoietic activity is so sparse that there are no cells to be withdrawn or when the marrow contains so many tightly packed cells that they cannot be suctioned out of the marrow. In such cases, a bone marrow biopsy would be advantageous. Before the bone marrow procedure is started, a peripheral blood smear should be obtained from the patient and a differential leukocyte count done.
- Collection Procedure
Follow standard precautions. Check for latex allergy; if allergy is present, do not use latex-containing products. Position the patient on the back or side according to site selected. The posterior iliac crest is the preferred site in all patients older than 12 to 18 months. Alternate sites include the anterior iliac crest, sternum, spinous vertebral processes T10 through L4, the ribs, and the tibia in children. The sternum is not generally used in children because the bone cavity is too shallow, the risk for mediastinal and cardiac perforation is too great, and the child may be uncooperative.
Shave, cleanse, and drape the site as for any minor surgical procedure.
Inject a local anesthetic (procaine or lidocaine). This may cause a burning sensation. At this time, a skin incision of 3 mm is often made.
Remember that the physician introduces a short, rigid, sharp-pointed needle with stylet through the periosteum into the marrow cavity.
Pass the needle-stylet combination through the incision, subcutaneous tissue, and bone cortex. The stylet is removed, and 1 to 3 mL of marrow fluid is aspirated. Alert the patient that when the stylet needle enters the marrow, he or she may experience a feeling of pressure. The patient may also feel moderate discomfort as aspiration is done, especially in the iliac crest. Use the Jamshidi needle for biopsy, although you can also use the Westerman-Jansen modification of the Vim-Silverman needle.
Remove the stylet and advance the biopsy needle with a twisting motion toward the anterosuperior iliac spine.
Rotate or “rock” the needle in several directions several times after adequate penetration of the base (3 cm) has been achieved. This “frees up” the specimen. Slowly withdraw the needle once this is done.
Push the biopsy specimen out backward from the needle. Use it to make touch preparations or immediately place in fixative. Make slide smears at the bedside.
Apply pressure to the puncture site until bleeding ceases. Dress the site.
Place specimens in biohazard bags, label properly, and route to the appropriate department.
- Patient Intervention Procedure
Instruct the patient about the test procedure, purpose, benefits, and risks.
Ensure that a legal consent form is properly signed and witnessed.
Bone marrow aspiration is usually contraindicated in the presence of hemophilia and other bleeding dyscrasias.
Reassure the patient that analgesics will be available if needed.
Be aware that bone marrow biopsies or aspirations can be uncomfortable.
