Category Archives: HEMATOLOGY

SOP REQUIREMENTS IN BLOOD TRANSFUSION (PART 1)

Use of blood, blood products and blood substitutes SOPs should contain:

  • Information which must accompany a request for blood.
  • How to calculate the volume of blood to use, particularly when the patient is a child.
  • Identity checks and documentation required when collecting blood from a patient, from the blood bank and before setting up a blood transfusion at the bedside of a patient.
  • Procedure to follow when a patient is being transfused and what action to take should there be an adverse reaction to the blood.
  • System for auditing how blood is used.

Donation of blood SOPs should contain:

  • Criteria for accepting a person as a blood donor and details of medical screen and pretesting procedures.
  • Questionnaire to be used with potential donors covering personal medical history and life style.
  • Policy and procedure for counselling donors with regard to HIV screening, testing and maintaining the confidentiality of blood donor information.
  • Details of how to collect blood from a donor.
  • Labelling donor blood.
  • Care of the donor following donation and frequency of donation.
  • Special requirements of mobile blood donation and transportation of blood.
  • Blood donation records.

Storage of blood SOPs should contain:

  • Temperature requirement, checking and recording the temperature of the blood bank refrigerator.
  • Sectioning of refrigerator and location of prescreened, screened, and crossmatched blood.
  • Procedure for checking the appearance of blood for signs of contamination before it is issued and documentation checks to be performed.
  • Blood bank records.
  • Locally important procedures, pertaining to the use and security of a blood bank refrigerator.

See also:

SOP REQUIREMENTS PART 2

BLOOD SAMPLE FOR ABO CELL & SERUM GROUPING


When grouping a donor, use the blood sample collected at the time of blood donation. Test it within 24–36 hours. When grouping a patient, collect 5–7 ml of venous blood into a dry glass tube and label
clearly. When completely clotted, centrifuge the blood at about 1 000 g for 3–5 minutes to separate the cells from the serum. Also collect an EDTA blood sample. Make a 3–5% washed red cell suspension as follows:

  • Transfer about 0.5 ml of EDTA blood (or red cells from a donor blood sample) into about 5 ml physiological saline.
  • Centrifuge at about 1 000 g for 2–3 minutes.
  • Discard the supernatant fluid, resuspend the sedimented red cells in a further 5–7 ml saline and centrifuge. Discard the supernatant fluid.
  • Make a 3–5% red cell suspension by mixing 1 drop of sedimented cells in 20–25 drops of saline (hold the Pasteur pipette vertically)

See also:

Antisera for ABO grouping

RHESUS BLOOD GROUP SYSTEM

Rhesus blood group system
The Rhesus (Rh) blood group system is next in importance to the ABO system in blood transfusion practice but it is not of equal significance in every country because the frequency of the most important of the Rhesus antigens, i.e. D antigen, varies in
different populations as follows:

Examples. Rhesus (D) positive
Asian. 90–98%
African 94–95%
Nepalese 99–100%
Oriental. 99–100%
South American people: 91- 97%
Ecuador, Chile, Brazil,
Argentina, Uruguay: 82–94%
Caucasian About 85%

Rhesus antigens

The Rhesus blood group system consists of six genes: Cc, Dd, Ee. A single chromosome can carry C but not c, D but not d, and E but not e. A person inherits from each parent a set of three closely positioned Rhesus genes, e.g. CDe/cde. At least 36 Rhesus genotypes are possible based on the combinations of genes that can be inherited ).


When using the Fisher-Race derived nomenclature, Rhesus antigens bear the same name as their genes, i.e. antigens D, C, c, E and e (d gene is not expressed).

Rhesus antigens are only expressed on
red cells. They are not found in body fluids.

Medically, antigen D is the most important of the Rhesus antigens because it is the most immunogenic, capable of producing immune (IgG) anti-D antibody which can cause haemolytic reactions. A person is grouped as Rhesus (Rh) positive or negative based on the presence or absence of antigen D:

  • Rh positive: A person inherits gene D and their red cells express antigen D.
  • Rh negative: A person does not inherit gene D and their red cells do not express antigen D.

ANTIBODIES OF ABO BLOOD GROUP SYSTEM

In the ABO blood group system, naturally occurring IgM anti-A and anti-B are present in the serum in the absence of the corresponding red cell antigen.

Although described as naturally occurring (allo-) antibodies, anti-A and anti-B are not detectable in the blood of newborn infants. The antibodies become detectable at about 3 months of age following exposure to A and B like substances present in the environment e.g. in bacteria and some foods.

As a person gets older the concentration of naturally occurring anti-A and anti-B in the blood becomes less and these antibodies may be difficult to detect in the serum of some elderly patients.

Occasionally IgG hyperimmune anti-A and anti-B can be found in the serum of group O persons in response to stimulation by A and B like antigens in the environment, and following pregnancy, or the injection of some vaccines or toxoids. In tropical
countries it is common to find lytic IgG anti-A, anti-B, or both in the fresh serum of up to 50% group O persons. Lytic anti-A is also found in group B persons and lytic anti-B in group A persons (about
25% of sera).

Serious haemolytic reactions can occur when Group O whole blood containing anti-A and anti-B haemolysins is used to transfuse non-group O persons. Immune IgG lytic anti-A and anti-B can cross the placenta and cause ABO haemolytic
disease of the newborn (HDN).

BACTERIALLY CONTAMINATED BLOOD

Bacterially contaminated blood
Transfusion of bacterially contaminated blood can cause fever, shock, collapse and death.

Blood most commonly becomes bacterially contaminated at the time it is collected when the venepuncture site is not
cleansed sufficiently or when a non-sterile blood collection set or blood collecting bag is used.

Blood must always be examined for signs of contamination at the time of use, i.e. when collected from the blood bank and at the patient’s bedside.

When grossly contaminated, blood appears haemolyzed and dark in colour. Some bacteria also cause clotting.

Bacteria which commonly contaminate blood are able to multiply in refrigerated blood.

HEALTH CHECK BEFORE DONATING BLOOD

● Basic physical examination: To include a check for swollen glands, skin rashes, signs of intravenous drug use or abnormal bleeding (purpura).

● Weight of the person: Persons weighing 45–50 kg or more can safely donate 450 ml of blood.

● Temperature of the person (to exclude any febrile disease e.g. malaria): A donor should not give blood when their temperature is raised.

● Measurement of blood pressure: A donor should not have an abnormally low blood pressure nor a high blood pressure. The upper acceptable limits are a diastolic pressure of 100 mm Hg and systolic pressure of 180 mm Hg. The minimum acceptable blood pressure is 90/50 mm Hg.

● Pulse rate of the person: The pulse rate should be regular and less than 100 beats/minute (counting for at least 30 seconds).

● Test to check for anaemia: For example, measurement of haemoglobin or PCV or an estimate of haemoglobin level using the Haemoglobin Colour Scale. In most countries persons are accepted as blood donors with a haemoglobin of 120 g/l (12 g/dl) or more and haematocrit of 380 g/l (38%) or more. In some countries the lower limit for men is set at 130 g/l (13 g/dl). Higher haemoglobin levels will be
required at high altitudes.

OBJECTIVES OF QUALITY ASSURANCE (QA) IN BLOOD TRANSFUSION


• To prevent unnecessary blood transfusions.

● To provide blood that is consistently safe and effective, traceable, and available when it is needed.

● To obtain blood from low risk healthy donors and promote non-remunerated voluntary blood donation.

● To ensure appropriate tests and controls are used to screen blood for transfusion transmissible pathogens, and to type (group) and compatibility test blood.

● To minimize errors by implementing concise easy to follow standard operating procedures (SOPs) and monitoring staff compliance.

● To prevent patient misidentification and errors in blood labelling, documentation, and blood records.

● To ensure personnel are well motivated and trained to the standard required with sufficient on-site experience and continuing education to perform blood transfusion related techniques competently and safely

D-DIMER AND FIBRINOLYTIC SYSTEM


Fibrinolysis is the enzymatic process used by the body to remove a fibrin thrombus to restore normal blood flow once damaged endothelium is repaired.
During the clotting process, tissue plasminogen activator (t-PA) released from the blood vessel wall and the plasma proenzyme plasminogen bind to the fibrin thrombus. When activated, plasminogen is converted to plasmin which degrades the
fibrin network, causing the clot to dissolve. During this process, fibrin degradation products (FDPs), i.e. fragments called D-Dimers are produced.

Raised FDP levels in DIC

In Disseminated intravascular coagulation (DIC), activated procoagulants are released into the circulation. Platelets and coagulation factors are consumed and fibrin is deposited in small vessels, activating the fibrinolytic system. The plasmin formed degrades the fibrin (also some fibrinogen), resulting in a build-up of FDPs in the circulation. The FDPs act as anticoagulants interfering with platelet function and fibrin stabilization.
Laboratory tests are available to semi-quantify D-DIMER in plasma.

THROMBIN TIME (TT) TEST PROCEDURE

(Courtesy of Diagen Thrombin Test Time Kit. Test )

Test the patient’s plasma and
control plasma in duplicate.

  1. Pipette 200 l (0.2 ml) of plasma into a small glass tube. Incubate at 37°C for 1–2 minutes.
  2. Add (0.1 ml) of thrombin, mix and start the stop-watch. Hold the tube in the water bath and tilt the mixture back and forth, looking for clot formation. When a clot forms, stop the stopwatch and record the time in seconds.
  3. Report the patient’s TT (average of the duplicate tests) providing the TT of the control plasma is satisfactory.

What are the normal ranges for TT?

12–15 seconds

What are causes of prolonged TT?

  • DIC and other conditions which produce a low fibrinogen level
  • Abnormal fibrinogen
  • Treatment with heparin
  • Liver failure
  • Presence of inhibitors of thrombin such as FDPs

See also:

TT test principle

THROMBIN TIME (TT) TEST

Thrombin time (TT) test
The TT test is sensitive to a deficiency of fibrinogen or inhibition of thrombin. It measures the formation of a fibrin clot by the action of thrombin on fibrinogen.

Principle of test
Thrombin is added to citrated plasma at 37°C. The time taken for the mixture to clot is measured and the appearance of the
clot noted.

Reagent
The use of a thrombin time test kit is recommended.
This provides the correct concentration of thrombin to use in the test, i.e. that which gives a clotting time of 12–15 seconds with pooled normal plasma.

Collect venous blood into citrate
anticoagulant and centrifuge to obtain platelet poor plasma as described for the APTT test. Perform the test with as little delay as possible.

See also:

Procedure for TT test