Laboratory Haematology as an Aid to Clinical Decision Making Flashcards
What is haematology?
Study of blood, blood-forming organs and blood diseases
What is blood?
Specialised fluid (technically a tissue or organ) composed of cells suspended in a liquid called plasma Only moving organ in body
Why study blood?
All organs (exception is cornea) have a vascular supply
How is blood tested?
Blood sample is in tube with anti-coagulant to prevent clotting, by trapping calcium that is involved with the coagulation cascade (tubes contain calcium chelators)
Placed in machine and, eventually, sample is retrieved:
rbcs settle at the bottom (fixed elements of blood)
Plasma sits on top
Two layers are separated by a buffy coat (wbcs and platelets)
Components of blood?
Formed elements (~45%) - rbcs, wbcs and platelets
Two types of wbcs:
Granulocytes - have granules and include neutrophils, eosinophils and basophils
Agranulocytes - have no granules and are mononucleated like lymphocytes and monocytes
Plasma (~55%) - which is ~90% water and also includes proteins (mostly albumin, immunoglobins, clotting factors), nutrients and salts
How are results generated?
Important to remember that measurements of formed elements of blood and plasma are done together, not separately
How to interpret laboratory results?
In context of:
Normal range for that age, sex, hospital, etc; is the result lower or higher?
Physiology
Balance between production and destruction/loss, e.g: if trauma results in blood loss, can lead to loss of more blood cells than the bone marrow can produce
Function of different types of cells and site of production?
rbcs - transport O2
wbcs - fight infection
Platelets - prevent bleeding
Majority produced in bone marrow
Structure of red cells?
Do not have a nucleus; have Hb instead (iron-containing protein with a haem group)
At centre of haem group is iron atom
Lack of iron leads to reduction in Hb and iron-deficient rbcs are smaller
Stroage iron is reflected by a protein called FERRITIN measured in serum (if ferritin is low, iron is low)
What is anaemia and how is it detected?
Reduced total rbc mass - not easy to measure in routine practice and Hb conc. is a surrogate marker
Methods of classifying anaemia?
By pathophysiology (balance between destruction and production) By morphological characteristics (features like size and contents of rbcs)
Pathophysiological classification of anaemia?
Increased loss/destruction of rbcs via bleeding of haemolysis (breakdown of rbcs)
or
Decreased production due to maturation abnormalities from when cell had a nucleus (erythropoiesis is present but is INEFFECTIVE), or cytoplasmic defects (like impaired Haemoglobinisation, due to lack of iron), or nuclear defects (like impaired cell division)
Could be hypoproliferative - reduced amount of erythropoiesis
Classification based on cell sizes?
Look at mean cellular volume:
MICROcytic - iron deficiency (e.g: chronic blood loss)
MACROcytic - vitamin B12/ folate deficiency can cause nuclear defects when cell still has a nucleus
NORMOcytic - in acute blood loss or in anaemia of CHRONIC disease (e.g: inflammation or infection) which is associated with decreased rbcs but normal sized
What is involved with anaemia of chronic disease?
AKA inflammation Cells of the reticuloendothelial system induce chages in: Iron homeostasis Proliferation of erythroid cells Production of erythroprotein Life span of rbcs
What can associate with macrocytic cells without anaemia?
Alcohol excess
Liver disease
Hypothroidism
Staining in blood film?
Combination of dyes:
One has affinity for nucleus - stains blue
One has affinity for cytoplasm - stains pink
Thus, can see rbcs (cells with no nucleus)
Reasons for using blood films?
To confirm abnormalities identified by analysers
To identify additional abnormalities not detected by analysers:
Target cells in liver disease
Rbc fragmentation, reflecting mechanical damage to circulation rbcs
Polychromasia - reflecting an increase in immediate red cell precursors, called reticulocytes
Summary of parameters to review in an anaemic patient?
Haemoglobin
rbc bount
Mean cellular volume (MCV)
Blood film report
Causes of high Hb?
May not be true increase, e.g: dehydration can lead to increased blood conc.
Secondary causes - e.g: hypoxia driven or erythropoietin tumours
When do neutrophils increase?
Main circulating phagocytes that increase with:
Stress - physiological/ pathological (acute infection, trauma, infarction and inflammation)
Steroids - cause de-margination (to centre of blood vessel, not to peripheries) so are more easily detected; this is NOT A TRUE CHANGE in neutrophils
Sometimes, will see “toxic”c changes in neutorphils on blood film comment (can occur in pneumonia)
When do eosinophils increase?
Parasitic infections
Hypersensitivity/allergic reactions
When do basophils increase?
Hypersensitivity reactions
When do mononuclear wbcs increase?
Monocytes - CHRONIC infection, malignancy, autoimmune disorders
Lymphocytes (numerous types and functions) - in viral infections (like glandular fever: reactive or activated lymphocytes
What is haemostasis?
Arrest of bleeding AND maintenance of vascular patency
Requirements for haemostasis?
Permanent state of readiness
Prompt response
Localised response
Protection against unwanted thrombosis
Steps in normal haemostatic system?
Formation of platelet plug - primary haemostasis
Formation of fibrin clot - secondary haemostasis
Fibrinolysis
Anticoagulant defences
Describe platelets, their structure and function
Small anucleate discs with a mean life span of 7-10 days
Damage to endothelial vessel wall cells exposes collagen
Platelet ADHESION occurs at injured site
Then SECRETION of various chemicals from platelets, leading to AGGREGATION of platelets at site of injury
Screening tests for primary haemostasis?
Platelet count
No simple screening tests for other components of primary haemostasis
Causes of low platelet count?
Is it genuine first of all?
Could be:
Liver disease
Rapid consumption of platelets (acute blood loss, coagulopathy), drug-induced, autoimmune destruction
Causes of high platelet count?
Generally, do not alter haemostasis (when between 450-1000 x 10 to power 9 platelets per litre) Could be: Acute blood loss Iron deficiency Inflammatory states Malignancies
How does fibrin clot formation occur?
AKA secondary haemostasis
Via an intrinsic or extrinsic pathway (come together to form factor X) that use calcium
Main points are:
Plasma = water + proteins (inc coagulation proteins/clotting factors)
Complex set of reactions involving different proteins/clotting factors is responsible for haemostasis
Clotting factors GENERALLY exist as an inactive protein, unless proteolytically activated
Activated clotting factors activate further coagulation reaction in presence of calcium
Reactions ultimately convert fibrinogen, soluble protein, to INSOLUBLE strands of fibrin, which, together with platelets, forms a stable thrombus
Brief version of how fibrin clot forms?
Initiation - tissue factor VIIa comes together with V/Xa, along with VIII/IXa
Causes propagation of prothrombin to thrombin (amplification via thrombin forming more VIII/IXa)
Fibrinogen is converted to the thrombus
Screening tests for fibrin clot formation?
Measure integrity of coagulation pathways:
Prothrombin time - measure TF/VIIa)
Activated partial prothrombin time - measures factor VIII and IX)
Causes of failure to form fibrin clot?
Multiple clotting factor deficiencies (usually acquires, e.g: Disseminated Intravascular Coagulation, liver disease or anticoagulant drugs, like warfarin
or
Single clotting factor deficiency - usually hereditary, e.g: haemophilia
What occurs in fibrinolysis?
Plasminogen converted to plasmin by tissue Plasminogen Activator (tPA)
Plasmin converts fibrin to FDPs (Fibrin degradation production), including D-dimers
What are D-dimers?
Fibrin degradation products measured in haematology lab
If increased, suggests an increase in fibrinolysis (following increased fibrin deposition, e.g: post-surgery, heart failure, malignancy and abnormal thrombus)
Use of D-dimer measurements?
D-dimer measurement can be combined with clinical scores to determine need for further investigation in patients with suspected thrombosis
Always use D-dimers with clinical score
What is plasma viscosity?
Index of changes in plasma proteins (reactant fibrinogen and some globulins)
Changes in plasma viscosity can reflect systemic inflammation and, less commonly, haematological malignancies producing an abnormal protein
