Haemotology Flashcards
What are the important causes of anaemia (5)
- blood loss
- haemolysis
- anaemia of chronic disease
- iron deficiency anaemia
- B12 or folate deficiency
What are some transfusion thresholds
- Don’t transfuse unless patient’s cardiovascular function is compromised
- Transfuse if Hb<70
- If above 70, assess cardio-respiratory status and then decide
How can we subdivide the causes of haemolytic anaemia
Acquired vs congential
Intravascular and extravascualr
Lab features associated with haemolytic anaemia
- Anaemia (normocytic).
- Increased serum unconjugated bilirubin (and conjugated)
- Increased urine urobilinogen
- Reduced serum haptoglobin
- Increased reticulocytes
- Increase LDH
- Urine haemosiderin (in intravascular)
What is extravascular haemolysis, where does it occur and give exmaples of its causes
Immature destruction of RBC’s due to injury to red cell membrane, opsonisation of red cells or reduced deformability.
Occurs in mononuclear phagocytic cells of spleen, liver and bone marrow.
- Hereditary elliptosis
- Heridtary spherocytosis
- G6PD (can be both)
- Sickle cell
- Auto immune (but can be both)
- Thalassemia
Causes of intravascular haemolysis
Essentially it is fragmentation haemolysis. When red cells are sheared over abnormal surfaces or the vessels are small.
MAHA
- HUS
- TTP
- Malignancy
- DIC/ infection (Malaria, Clostridium)
- HELLP/ pre-eclampsia
- Malignant hypertension
- AV malformation
Abnormal surfaces
- Prosthetic heart valves, grafts, perivalvular leaks
Misc
- G6PD (which is both)
- Mismatched blood transfusion
- Immune hemolytic anaemia (autoimmune, drug, infection)
- Unstable Hb disease
- March Hemoglobinuria
- Paroxysmal nocturnal hemoglobinuria
How do you approach investigating anaemia
MCV 80-100 - Normocytic
Reticulocytes >2
- Bleeding
- Haemolysis
Reticulocytes <2
- Bone marrow mischief
MCV >100 - Macrocytic
Presence of hypersegmented neutrophils
- B12
- Folate
- Drugs (Classically phenytoin)
Absence of hypersegmented neutrophils
- Alcohol
- Liver disease
- MDS
- Toxins
MCB <80 - Microcytic
IDA
- Reduced ferritin
- Reduced transferrin saturation (because we have increased our transferrin)
Thalassemia
- Increased ferritin
- Reduced RCC (red cell count)
Anaemia of inflammation/ anaemia of chronic disease
- Increased ferritin
- Normal/ Increased transferrin saturation (becaused we have reduced our transferrin, therefore the ratio increaseas)
Explain how iron is absorbed
Two main forms of iron
Ferris/ haem iron - Fe 2+
Ferric iron/ non haem iron - Fe3+
Non heam irone from diet (NOT MEAT) arrives in Ferric form to the small intestine.
Cannot be absorbed in Ferric form, needs to be converted to Ferris form.
DMT1 (co-transporter with hydrogen) and Vitamin C ferroreductase are present on the apical surface of the enterocyte.
Vitamin C ferroreductase reduces iron to Ferris form.
Ferris iron then enters the enterocyte by DMT1, it is then oxidised back to Ferric iron.
Iron leaves the cell through the basal surface by Ferroportin. It has to be in the Ferric form in order to be transported around the body.
Hephaectin is the enzyme that does this once through the Ferroportin transporter.
Transferrin transports ion around the body, as it cant travel by itself. It binds TWO ferric irons. Normally it is 35% saturated.
Two main fates of iron.
- Erythropoiesis in bone marrow 70%
- Goes to liver to be stored as Ferritin.
Compare hereditary elliptocytosis to spherocytosis
Similar clinical and laboratory
features to hereditary spherocytosis
except for blood film
Clinically milder disorder
Defect in horizontal interactions
What is hereditary spherocytosis and how is it passed on.
Most common hereditary haemolytic anaemia in northern Europeans
Due to abnormal red cell protein
Autosomal dominant
Structure of Hb
Each hemoglobin molecule is made up of four heme groups surrounding a globin group.
Clinical manifestations of hereditary spherocytosis(4)
Jaundice fluctuates
Most patients have some
splenomegaly
Pigment gallstones common
Aplastic crises can occur if contracts parvovirus B19 infection
Treatment of hereditary spherocytosis
Splenectomy if symptomatic
anaemia, gallstones
Diagnosis of hereditary spherocytosis
(film, flow and DAT)
Film: spherocytes and reticulocutes
Flow cytometry: less eosin-5-
maleimide
DAT negative
How many types of Hb do we have and what chromosmes are they on
Normal adult blood has 3 types of
haemoglobin
A, A1 and F
A
- 2 alpha 2 beta
A1
- 2 alpha 2 delta
F
- 2 alpha
- 2 gamma
Alpha is coded for on chromosome 16 and is duplicated – 2 on each chromosome
Beta, gamma and delta occur on
chromosome 16
Describe the coagulation cascade (dont need to include degredation)
Composed of the extrinsic and intrinsic pathway which both lead onto the common pathway resulting into an organised clot.
The extrinsic pathway (PT) is activated by exposed TF and is considered the primary initating event of the clotting cascade.
7>7a
The small amount of thrombin made by the extrinsic pathway activates the intrinsic pathway which amplifies the whole clotting cascade.
APTT (intrinsic) (tenet)
12 > 12a
11 > 11a>
9 > 9a
8 > 8a
- Carried by vWF, because it increases factor 8 half life
- Factor 2 (Thrombin) release 8 from vwf
Common pathway
- 10a + cofactor 5a = 2> 2a (pothrombin to thromrbin)
- 1> 1a (fibrinogen to fibrin)
- Fibrin reinforces the platelet plug.
Calcium is involved in a few of the steps.
How do we break down a clot i.e describe fibrinolysis. and how do we switch off the clotting cascade (anti thrombotic pathway).
Fibrin broken down to fibrin degradation products including D-dimer this is done by the eznyme plasmin.
Plasminogen is converted to Plasmin by T-PA. Thrombin activates t-PA (essentially by turning off the break).
Thrombin binds to Thrombomodulin (protein on endothelial cell surface). This complex activates Protein C (and its co-factor Protein S). These work to inhibit factor 5 and 8.
Antithrombin inhibits proteases 9, 10, 2
What is our daily requirment for iron
How much do we lose
10-20mg
Men lose 0.6 mg/d of iron - in stools
Women lose twice as much due to menstruation
When do transferrin levels go up and down
Down in inflammation and infection - a way of hiding iron from bugs
Up in Iron deficiency - as a means to try to achieve homeostatis
What is transferrin saturation, when would it be increased.
The amount of iron that is bound to transferrin.
Increased in haemochromatosis and post transfusion.
What things improve absorption of iron and what reduces it
Improved by
- Vitamin C
- Ferrous Form
- Low iron stores in the body
- Low pH (changes Fe3+ to Fe2+)
Reduced by
- Tannins
- inflammation
- Calcium
- Phytic acid in cereals
- High pH (i.e pH of panc juice)
- Phosphates
- Oxalates
How do we regulate our iron levels (and what stimulates it)
Hepcidin is a peptide hormone produced by the liver, its main function is to inhibit Ferroportin. It prevents iron being released into circulation i.e it decreases plasma iron conc. It also prevents Hepcidin being absorbed.
Stimulated by
- inflammtory cytokines like IL-6
- increased plasma iron conc/ iron bound to transferrin
- LPS.
- HFE protein (made by the haemochromatosis gene).
What is G6PD (clinically, what is seen on film)
X linked disorder that makes the RBC more susceptible to oxidative stress (i.e ROS), because G6PD is the only way that RBC’s get NADPH. Makes the cell membrane susceptible to damage.
Wee see Heinz bodies as the ROS also damages the Hb denaturing it. These Heinz bodies attach to the membrane of the RBC reducing its flexibility.
The macrophages in the spleen see this Heinz body and take a “bite out of the erythrocyte”. See reticuloytsosis. See blister cells too.
Heinz bodies also damage membrane directly so we get intravascular and extravscaular haemolysis (extra vascular being from spleen macrophages)
Only older RBC’s are targeted therefore the haemolytic episode of self limiting and stops when only young RBCs are present.
What is G6PD protective against
It is protective against falciparum malaria (I.e the parasite infected RBC is also killed by the oxidative stress).
Geographic distrubtion of G6PD (and compare severities/ variants)
West African (mild)
South-East Asia (more severe)
Mediterranean, the Middle East (most severe due to much lower levels of GPPD)
G6PDA - only occurs in older RBC’s
What causes a haemolytic episode in G6PD
Exacerbated by anything that increases ROS and puts us under oxidative stress
Infections and severe acute illness (e.g DKA)
Drugs
- Antimalarias (Primaquine, chloroquine, Pam Aquino)
- Sulphonamides (TMP, co-trimox)
- Abx - Chlorampenicol, Probenicid
- Aspirin
- NSAIDS
Moth balls (naphthalene)
Fava beans
Explain the role of G6PD enzyme
Glutathione is an antioxidant that helps mop up free radicals.
To do this it needs to be in a reduced state so that it can donate an electron.
Donation of this electron leaves Glutathione in an oxidised state unable to work.
The glutathione reductase enzyme uses NADPH to give an electron to glutathione.
NADPH is now NADP+. G6PD is the enzyme that reduces NAP+ to NADPH (it uses G6P ie glucose to do this which is a very reliable energy source)
What is DIC
Widespread inflammation (and therefore endothelial damage) which causes widespread activation of the clotting cascade.
This results in inappropriate fibrin deposition and consumption of clotting factors.
Resulting in bleeding and clotting.
Biochemical features of DIC (including film)
Low platelets
Low fibrinogen
Prolonged thrombin time
High D-Dimers
+/- prolonged PT and APTT
Red cell fragmentation (schistocytes) on blood film
Causes of DIC
Infections
- Clostridium
- Malaria
- Gram negative and meningococcal sepsis
- Gram positive sepsis
- Viral infections
Malignancy
- Acute promyelocytic leukemia
- Widespread mucin secreting adenocarcinoma
Hypersensitivity
- Anaphylaxis
- ABO incompatibility
Obstetric complications
- AFE
- Preeclampsia
Misc
- Panc
- Snake bites
- Heat stroke
- Massive blood loss
Consequences of DIC
Haemolytic anaemia (deposition of fibrin within microvasculature)
Renal failure
- Thrombi in renal glomeruli
- Microinfarcts
- Bilateral renal cortical necrosis
- Oliguria
- ARF
Haemorrhagic diathesis
- Circulatory failure and shock
Circulating anticoagulant substances
- fibrinogen breakdown products
Lungs
- microthombi in alverolar capillaries
- ARDS
- Dyspnea
- Cyanosis
- Extreme resp. difficulty
Brain
- Microinfarcts
- Fresh bleeding
- Convulsions
- Coma
Adrenals
- Massive haemorhage
- waterhouse-friderichsen syndrome (seen in meningococcemia)
Placenta
- Widespread thombi
- Atrophy of cytotrophoblast and syncytiotrophoblast
What is the only cause of a short APTT
Due to a bad draw
Does DIC cause neutropenia
Neutropenia has nothing to do with DIC
WBC not consumed in the process
Factors which tend to localise and limit thrombocoagulation are
- clearance of activated prothombocoagulants
- local degradation of clotting factors
- secretion of protease inhibitors by adjacent intact endothelium
Antithrombin III
- Function
- Clinical mafiestation of deficiency
- Treatment
- deficiency causes recurrent phlebothrombosis
- antagonizes the actions of a wide spectrum of activated serum proteases
- deficiency may be successfully treated with low dose aspirin
List 5 acquired coagulation disorders
- vitamin K deficiency and warfarin overdosage
- liver disease
- inhibitors of blood coagulation
- massive transfusion
- DIC
Who gets Vit K deficiency and how do we treat it
- People who havent eaten in days (but more likely if starvation has extended for a week or 2).
- Patients with nausea, vomiting or anorexia, or those in an intensive care situation .
- Obstructive jaundice
Can be given PO, IV or IM
- Has to be given IV/IM in obstructive jaundice
- IM not always effective, may be lost in a haematoma formed in the muscle at the site of injection.
- Has to be mixed with saline if given IV and administered slowly (no faster than 1mg/min)
Is Vit K helpful in liver disease
No unless there is a component of biliary obstruction
What coags are derranged in severe liver disease as well as on CBC
- PT, INT and APTT
- Fibrinogen level may be reduced
- Thrombocytopenia common
What improves haemostasis in liver disease
FFP