Immunohematology Laboratory

CHAPTER 10


Immunohematology Laboratory



Objectives


At the end of this chapter, the reader should be able to do the following:


1. Determine the approximate increase in hematocrit and hemoglobin in patients receiving packed red blood cells.


2. Calculate the expected decrease in prothrombin and partial thromboplastin time in patients receiving fresh frozen plasma.


3. Calculate the approximate increase in platelet count in patients receiving pooled platelet concentrate or a platelet pheresis pack.


4. Calculate the appropriate dose of Rh-immune globulin to be given to Rh-negative patients.


5. Determine the percentage of compatible (or incompatible) units of blood in 100 random donors when patients have multiple antibodies.



CALCULATIONS ASSOCIATED WITH THE MEDICAL EFFECTS OF TRANSFUSION SERVICES


Immunohematology is the science of blood group serology and transfusion medicine. A more common name for the immunohematology laboratory is the blood bank. The primary function of the immunohematology laboratory is to supply the safest and most suitable blood and blood products to patients as quickly as possible. Surgical, trauma, maternity, and orthopedic patients are only a few of the types of patients that may require transfusion services. Routine blood products provided by the laboratory include packed red blood cells (RBCs), fresh frozen plasma, and platelet concentrates. When individuals donate a pint (or approximately 450 mL) of whole blood, that blood is referred to as a “unit.” The average adult body’s total blood volume is between 7 and 10 pints or units of blood. The whole blood unit may be processed to provide three or more components, including packed RBCs, plasma, and platelets. The whole blood is centrifuged, and the plasma is expressed into an attached satellite bag. The RBCs left behind are referred to as a “unit” of packed RBCs. The plasma may be further centrifuged, and the platelets are expressed into a second satellite bag. In this manner, both a unit of fresh plasma and a unit of platelet concentrate are formed. The immunohematology laboratory performs tests to determine the compatibility between the patient’s (recipient) blood and donor blood. Only when a unit has been extensively tested for compatibility with the patient is it transfused into the patient.



Determining Therapeutic Effects of Transfusions


In this era of HIV and other blood-borne pathogens, the decision to transfuse blood into a patient is not made lightly. In most cases, the patients are severely anemic, profusely bleeding, or undergoing major surgery. Patients who are severely anemic may require an infusion of packed RBCs to increase the oxygen-carrying capacity of the blood. Plasma may be given to patients who require an infusion of coagulation factors, whereas platelets may be given to patients with decreased platelet quantity or function. Patients on chemotherapy frequently require the transfusion of platelets. Determining the actual therapeutic effect of a unit of packed RBCs, plasma, or platelet concentrate on the patient can assist the physician in determining the number of units of blood or components to be transfused.



Determining Hemoglobin Increments


Because a unit of packed RBCs is highly concentrated with RBCs for each unit of packed cells that is transfused into a patient who is not bleeding, the patient’s hemoglobin concentration can be expected to increase by 1 g/dL. This ratio does not hold true if the patient is actively bleeding.





Example 10–1

An 87-year-old patient was admitted to the medical unit of a hospital while suffering from chronic renal failure. The patient was severely anemic, with a hematocrit of 12% and hemoglobin of 4.0 g/dL and received five units of packed RBCs. What would be the patient’s expected hemoglobin concentration posttransfusion?


The hemoglobin concentration is expected to rise 1 g/dL for every unit of packed RBCs in nonbleeding patients. As this patient received 5 units of packed RBCs, it is expected that the posttransfusion hemoglobin concentration should be approximately 9.0 g/dL.




Determining Hematocrit Increments


One unit of packed RBCs has a hematocrit of approximately 79%. For every unit of packed RBCs, the hematocrit can be expected to rise 2 to 3 percentage points in a patient who is not bleeding. As with hemoglobin, this ratio does not apply if the patient is actively bleeding.





Example 10–2

A woman delivered a child by cesarean section, during which she bled quite heavily. Three days after delivery, the hematocrit was 18%. Her physician ordered 3 units of packed RBCs to be administered. How will this affect the hematocrit?


For every unit of packed RBCs transfused, the hematocrit is expected to increase by 2 to 3 percentage points. As this patient received 3 units of packed RBCs, her hematocrit should rise to between 24% and 27%.




Determining Fresh Frozen Plasma Increments


The plasma that is expressed from a unit of packed RBCs is further centrifuged to remove the platelets into a separate unit. The units of plasma are frozen within 8 hours of collection to preserve all coagulation factors. Before they are used, the fresh frozen units are thawed in a 37° C water bath or FDA-approved microwave or other approved device specifically designed to thaw plasma. The fresh frozen plasma units contain all coagulation factors, and 2 units are usually sufficient to increase clotting factor activity by 15% to 20% in a patient with diminished clotting capacity.





Example 10–3

A patient with a history of spontaneous bleeding and bruising had an increased prothrombin time. Two units of fresh frozen plasma were transfused. What effect will this have on the prothrombin time?


For every 2 units of fresh frozen plasma, the clotting factors are elevated by 15% to 20%. By transfusing 2 units, the prothrombin time should be approximately decreased 15% to 20%.




Determining Platelet Increments


The normal concentration of platelets in a healthy person is between 150,000 and 450,000/μL of whole blood. Patients with bone marrow abnormalities, such as leukemia, may have diminished platelet production and may develop life-threatening drops in their platelet counts. Platelet concentrates are formed when plasma components are further centrifuged at high speed. All but approximately 50 mL of plasma are expressed off to form the plasma concentrate. The remaining 50 mL is the newly formed platelet concentrate that contains approximately 5.5 to 7.0 × 1010 platelets. Each unit will increase the platelet count by an increment of approximately 10,000/μL, which is not sufficient to provide a significant platelet increment in the patient. Routine practice advocates the administration of 6 to 10 platelet concentrates that have been pooled. The expected increment will vary depending upon the number of platelet concentrates pooled and the product transfused. A valid posttransfusion platelet count cannot be performed sooner than 6 hours after the completion of an active bleeding episode.


Platelet donors are persons who donate their platelets to patients by the process of apheresis. The apheresis instrument separates the platelets from the blood. All other constituents of the blood, except approximately 200 to 400 mL of plasma and a small number of RBCs, are returned to the donor. In this manner, large quantities of platelets may be harvested without harm to the donor. One pheresis pack is equivalent to approximately 10 to 12 platelet concentrate units. Therefore the total number of platelets donated is approximately 5.5 × 1011 to 8.4 × 1011 per pheresis pack.




Related posts:

  1. Quality Assurance and Quality Control in the Clinical Laboratory
  2. Urinalysis Laboratory
  3. Dilutions and Titers
  4. Calculations Associated with Solutions

Stay updated, free articles. Join our Telegram channel
Tags:
Nov 18, 2017 | Posted by in PHARMACY | Comments Off on Immunohematology Laboratory

Full access? Get Clinical Tree
Get Clinical Tree app for offline access