Paeds - Haematology Flashcards
what makes up adult haemoglobin?
4 protein sub-units made of two pairs of sub-units
2 alpha and 2 beta sub-units
what makes up foetal haemoglobin?
4 protein sub-units made up of 2 alpha and 2 gamma sub-units
why does foetal Hb need to be different?
adult Hb picks up O2 in the lungs
foetal Hb picks up O2 in the placenta and has to steal it from mothers Hb
which has a greater affinity for O2, adult or foetal Hb?
foetal (o2 binds easier and is more reluctant to let go basically)
adult vs foetal Hb on oxygen dissociation curve?
foetal has a steeper upward slope
(ie adult Hb needs a higher partial pressure of O2 to “fill up” with oxygen wherease foetal Hb will “fill up” with O2 at lower concentrations of O2)
how does Hb change during development?
production of foetal Hb decreases from 32-36 weeks gestation
during this time, production of adult Hb increases
over time there is a gradual transition from HbF to HbA
how does Hb change after birth?
at time of birth, total Hb is 50% foetal and 50% adult
by 6 months old very little HbF is produced and eventually all RBCs will contain only HbA
how is foetal HB affected in sickle cell disease?
sickle cell disease is a genetic abnormality in area coding for beta subunit of Hb
foetal Hb doesnt have a beta subunit so there is no sickling of RBCs (until adult Hb is the prominent type of Hb)
what can be used to increase production of HbF in patients with sickle cell anaemia?
hydroxycarbamide
has protective effect against sickle cell crises and acute chest syndrome
what is sickle cell anaemia?
genetic condition causing sickle (crescent) shaped RBCs which makes them more fragile and easily destroyed leading to a haemolytic anaemia
what causes sickle cell anaemia?
autosomal recessive condition where there is an abnormal gene for beta globin on chromosome 11
patients with sickle cell have an abnormal variant of Hb called HbS which causes RBCs to be abnormal sickle shape
sickle cell trait vs disease?
one cope of abnormal gene for beta globin = sickle cell trait (usually asymptomatic)
two copies = sickle cell disease (symptomatic)
how is sickle cell disease related to malaria?
more common in patients from areas traditionally affected by malaria
having one cope of the gene (sickle cell trait) reduces severity of malaria
how is sickle cell diagnosed?
pregnant women at risk of being carriers of the gene are offered testing in pregnancy
sickle cell disease is also tested for on the newborn screening heel prick test at 5 days old
possible complications of sickle cell disease?
anaemia increased risk of infection stroke avascular necrosis of large joints (eg hip) pulmonary hypertension painful and persistent penile erection (priapism) chronic kidney disease sickle cell crises acute chest syndrome
general management of sickle cell disease?
avoid dehydration and other triggers of crises
ensure vaccines up to date
antibiotic prophylaxis (usually with penicillin V)
hydroxycarbamide can stimulate HbF production
blood transfusion for severe anaemia
bone marrow transplant can cure
what is a sickle cell crisis?
umbrella term for a spectrum of acute crises related to the condition
range from mild to life threatening
can occur spontaneously or triggered by stresses
what can trigger sickle cell crisis?
infection
dehydration
cold
significant life events
how is sickle cell crisis managed?
supportively
- treat any infection
- keep warm
- keep hydrated (may need IV fluids)
- simple analgesia
- treat priapism with penile aspiration
4 types of sickle cell crisis?
vaso-occlusive crisis (AKA painful crisis)
splenic sequestration crisis
aplastic crisis
acute chest syndrome
what is a painful crisis?
causes by sickle shaped RBCs clogging capillaries and causing distal ischaemia
symptoms of painful crisis?
pain
fever
symptoms of triggering infection (if present)
can cause priapism in men by trapping blood in penis
what can cause painful crisis?
dehydration
infection
high haematocrit
what is splenic sequestration crisis?
where RBCs block blood flow within the spleen
causes acutely enlarged and painful spleen
pooling of blood in the spleen can lead to severe anaemia and circulatory collapse
how is splenic sequestration crisis managed?
emergency
supportive management
blood transfusions and fluid resuscitations used to treat anaemia and shock
splenectomy used as preventative measure in cases of recurrent crisis