Haematology Flashcards
How often can a male donor donate blood
• Male donors can donate 470 ml of blood up to four times a year
How often can females donate blood
Female donors can generally donate 470 ml of blood every 16 weeks (to reduce the risk of
developing iron deficiency anaemia)
How often can platelet donors donate blood
Platelet donors can donate up to 24 times a year (minimal interval between donations is 14 days)
what are the lower limits of hb for a man
typically 130g/L
what are the lower limits of hb for a female
115g/L
Describe a unit of red cells
180–200 ml packed red cells 100 ml optimal additive solution 20ml residual plasma *total volume >300ml* haematocrit typical 0.55 leucocyte depleted * Can be stored for up to 5 weeks at 4oC +/- 2 * can be irradiated or CMV negative
what is the transfusion threshold if
< 65 years old with no cardiovascular or cerebrovascular problems
Usually only consider transfusion when Hb < 70 g/L
What is the transfusion threshold if
> 65 years old with no cardiovascular or cerebrovascular problems
Usually only consider transfusion when Hb < 80 g/L
what’s the transfusion threshold if
Known cardiovascular or cerebrovascular history (previous myocardial infarction, angina, hypertension, heart failure, peripheral vascular disease pulmonary oedema)
Usually only consider transfusion when Hb < 90 g/L
what is the transfusion threshold if
Patients with symptoms due to anaemia
Unstable patients bleeding heavily
Impaired marrow function
Consider transfusion when Hb < 100 g/L
describe Transfusion Associated Circulatory Overload (TACO)
Usually due to rapid or massive transfusion of blood components in patients with diminished cardiac reserve or chronic anaemia
• Vulnerable patients (> 70 years old, low body weight, cardiac failure, renal failure, hypoalbuminaemia or fluid overload)
• Clinical features include dyspnoea, orthopnoea, cyanosis, tachycardia, hypertension and pulmonary oedema
what is the normal platelet count
• The normal platelet count is 150–450 × 10/L
what are the two methods of production of platelet donations
Pooled Platelets
• Four whole blood donations are separated, the buffy coats are pooled and are then re‐ suspended in donor plasma
• Pooled product = higher donor exposure
Apheresis Platelets
Platelet‐rich plasma is collected by a machine while the remaining blood constituents are returned to the donor
Single donor = lower donor exposure • Higher yields
• Greater consistency
• HLA/HPA matched donors
what’s in a pack of pooled platelets
At least 240 × 10 platelets
• 250 ml of plasma (may cause transfusion
• Can be stored for up to 5 days (7 days if bacteriologically screened) at 22°C +/− 2°C and on a special agitator rack
reactions)
• 60 ml of anticoagulant
• Total volume 310 ml
• Leucocyte depleted
• May be irradiated or CMV negative depending on the clinical indication
what is the adult therapeutic dose for platelets
One pack (apheresis or pooled) is sufficient for an adult therapeutic dose (ATD) • One ATD should increase the platelet count by at least 20 10/L (typically 20–40 × 10/L in a 70 kg adult)
what are the BCSH guidelines for the use of platelet transfusions
Prophylaxis of haemorrhage in patients with platelet count < 10 × 10/L
• Thrombocytopenia with haemorrhage
• Disseminated intravascular coagulation
• Massive transfusion
• Platelet function disorders
• Cover for surgery or invasive procedure
list some contraindications to platelet transfusion
- Platelet transfusions are usually contraindicated in:
- Thrombotic thrombocytopenic purpura (TTP)
- Heparin‐induced thrombocytopenia (HIT)
- Idiopathic thrombocytopenic purpura (ITP)
- Post‐transfusion purpura (PTP)
• But may be given in the context of life‐threatening haemorrhage
what’s in a unit of fresh frozen plasma
One donor per unit
• Typical plasma volume is 220 ml (varies)
• Anticoagulant volume 50 ml
• The unit volume can vary from 200–300 ml
• Fibrinogen concentration 20–50 g/L
• Factor VIII concentration > 0.7 IU/ml
• Stored at −25°C or below for up to 2 years
what are the BCSH guidelines for transfusion of fresh frozen plasma
Coagulation factor deficiency where no factor concentrate is available
• Acute disseminated intravascular coagulation with evidence of bleeding
• Thrombotic thrombocytopenic purpura (TTP)
• It may also be indicated in some other conditions with abnormal bleeding and coagulopathy, e.g. massive transfusion, liver disease and cardiopulmonary bypass
• FFP should never be used for the reversal of Warfarin anticoagulation when there is no evidence of severe bleeding
• FFP should not be used in the management of hypovolaemia
normal plasma fibrinogen level
• The normal plasma fibrinogen level is 1.9–4 g/L
describe the preparation of cryoprecipitate
Cryoprecipitate is prepared from fresh frozen plasma by thawing at 2–6°C
• It is a pooled component (5 donations)
• It is stored at −25°C or below for up to 2 years
• An adult dose consists of 2–4 units
• Methylene blue‐treated and removed cryoprecipitate, made from imported FFP, is available for patients born after December 1995
BCSH Guidelines for Transfusion of Cryoprecipitate
The most common indication for transfusion of cryoprecipitate is to enhance fibrinogen levels in:
• Dysfibrinogenaemia
• Acquired hypofibrinogenaemia as seen in massive transfusion and disseminated intravascular coagulation
• Treatment is usually indicated if the plasma fibrinogen level is < 1 g/L
what temperature are platelets stored at
22oC
what temperature is fresh frozen plasma stored at
-4 oC
Indications for the Coagulation Screen
• Clinical suspicion of a bleeding disorder
• Note that Von Willebrand Disease, factor XIII deficiency and platelet dysfunction can give rise to a
normal coagulation screen • Acutely bleeding patient
• Paracetamol overdose
• Liver disease
• Monitoring transfusion requirements
what are some problems with blood samples that can affect blood screen
- Stress, exercise
- Can shorten the APTT due to elevated factor VIII levels
- Blood taken from in dwelling line
- Dead space from a butterfly line
- Delay in transport to the laboratory
- Patient haematocrit
- Excessive venous occlusion
- Traumatic venepuncture
list some causes of prolonged APTT
• Intrinsic pathway
- DIC
- Liver disease
- Massive transfusion
- Unfractionated heparin therapy monitoring
- Heparin contamination from line locks
- Oral warfarin therapy (APTT less affected than PT)
- Lupus anticoagulant (antiphospholipid syndrome)
- Deficiency of VIII, IX, XI, XII
- Factor XII deficiency does not cause bleeding unlike the other factors
what is the APTT correction study
Patient plasma mixed with normal plasma, which contains all clotting factors at their normal level
• If APTT result ‘corrects’ suggestive of underlying clotting factor deficiency
• If APTT result fails to correct, need to exclude the presence of a lupus anticoagulant
indications for d-dimer
Suspected DIC
• Assessment of thrombolytic therapy
• Suspected VTE when used with a clinical prediction model, e.g. Wells score
describe forward grouping
Forward grouping is used to test for the presence of A and B antigens on patient red cells • 3–5% suspension of patient red cells is prepared
• Monoclonal anti‐sera (anti‐A, anti‐B) added
• Haemagglutination indicates presence of antigen
describe reverse grouping
Reverse grouping is used to test patient plasma for anti‐A and anti‐B
• It is a valuable confirmation of forward grouping
• Patient plasma is added to suspensions of group A1 red cells and group B red cells
• Haemagglutination indicates presence of antibody
describe antibody screening test
Used to screen patient plasma for clinically significant red cell antibodies other than anti‐A and anti‐B
• Patient plasma is incubated with a panel of screening reagent red cells which is known to express the range of clinically significant blood group antigens (indirect anti‐globulin test – IAT)
• Haemagglutination indicates the presence of a red cell antibody
• The screening test is not designed to identify the specificity of the antibody/antibodies
what is the universal recipient blood group
AB
what is the universal donor blood group
O
what is alpha thalassaemia
a thalassaemia occurs when there is a genetic defect in one or more of the a globin genes leading to failure of production of the globin protein.
• a thalassaemia trait is the usually symptomless carrier state
• It is common amongst people whose origins are South east Asian or eastern Mediterranean
• If both parents have a0 thalassaemia trait, the foetus can inherit the severe disease Hb Barts or Hydrops Foetalis which leads to death of the baby ‘in utero’ or soon after birth and can cause serious clinical problems for the mother during her pregnancy
describe Beta thalassaemia
B thalassaemia occurs when there is a defect in the B‐globin gene resulting in failure of production of the B‐globin protein
• B thalassaemia trait (the symptomless carrier state of beta thalassaemia major) is common in many parts of the world particularly the Mediterranean, the Middle East, many parts of the Indian subcontinent, Southeast Asia and Pacific Island populations
• If both parents have B thalassaemia trait the foetus can inherit the serious condition B thalassaemia major, which requires a life‐long treatment of monthly blood transfusions and nightly infusion of an iron chelator for survival
what are some issues for parents if their child is born with thalassaemia
Microcytic but not necessarily iron deficient – need ferritin measured for assessment of iron status
• Carrier and therefore inheritance for future generations
• Protection against malaria
describe sickle cell disorder
Sickle cell disease is caused by a single mutation in the B‐globin gene at position 6 leading to an amino acid change of glutamic acid to valine
• Sickle cell trait (the symptomless carrier state of sickle cell disorder) is common in many parts of the world particularly tropical Africa, West Africa, the Middle East, India and parts of the world such as the Caribbean islands and South America with large numbers of migrants from these islands
• If both parents have sickle cell trait, the foetus can inherit sickle cell anaemia
- enlarged spleen
bony lesions
cerebral infarcts
what is the neonatal screening test for sickle cell anaemia
heel-prick test
describe flow cytometry
Cells in suspension pass in single‐file through a laser beam at an appropriate wavelength
• The cell momentarily breaks the beam and scatters the light
• Ifafluorochrome‐conjugatedantibodyis bound to the cell, light is also emitted
• Light is collected by a combination of filters, mirrors and detectors and data collected
Cells populations can be identified by: - Physical characteristics (Scatter): • Size • Complexity, e.g. Cytoplasm granularity - Antigen expression (Fluorescence): • Surface • Cytoplasmic
describe the process of cytogenetics
- Culture cells (bone marrow/blood)short‐ term
> Stimulate cells to divide (mitosis)
• Arrest cell division in metaphase stage
> Colcemid (spindle poison)
> Chromosomes attached to the spindle and lined up in the middle of the cell
• Giemsa staining
> Produces specific banding patterns along the chromatids
• Examine under high power microscope to identify chromosomes –> karyotype
Describe Fluorescence In Situ Hybridization (FISH)
Single‐stranded DNA probe anneals to its complementary sequence in the target genome: to detect and localise specific DNA sequences
• Fluorescence microscopy examines the location of the probe bound to the chromosomes
describe some advantages of FISH
Advantages of FISH
• Can visualise abnormalities in non‐dividing cells as well as metaphases (interphase analysis)
• Can be performed on directly prepared samples
• More rapid results
• More cells can be analysed
• Cryptic rearrangements can be detected
• Complex rearrangements can be characterised
• Can be performed on tissue sections, e.g. Bone marrow trephine biopsies
what are primers in PCR
Primers: short segments of nucleotides (20–30 bases) which are complementary to target sequences of DNA flanking the region to be amplified. Provide the initiation site for elongation
what is tax polymerase in pcr
Taq polymerase: the thermostable enzyme which extends the primers by sequential addition of nucleotides to synthesise a complementary DNA strand from the template
what is Deoxynucleoside triphosphates (dNTPs) in PCR
Deoxynucleoside triphosphates (dNTPs): the building blocks used by Taq polymerase to synthesise the new DNA strand (dATP, dCTP, dGTP, dTTP)
what temperature does denaturing occur in PCR
95oC
what temperature does taq polymerase work at in PCR
72oC
describe the clinical applications of PCR in haematology
assessment of clonality of lymphoid proliferations
Molecular monitoring
