G6PD deficiency Flashcards
What is G6PD and how does it arise?
o Sex-linked mutations causing a deficiency in the enzyme G6PD.
o This means there is less NADPH being produced, and therefore less reduced glutathione.
o As there are decreased levels of reduced glutathione, the RBCs are susceptible to oxidative stress. This causes them to lyse and release their haemoglobin intravascularly, following intravascular haemolysis where the free Hb binds to haptoglobin. This complex is then removed by RES macrophages, and excess haemoglobin is directed to the kidneys to be excreted in urine.
What are the symptoms and their explanations?
o Mostly asymptomatic when there are no oxidative stresses present. Oxidative stresses include eating fava beans (have an oxidative chemical in), being on antibiotics, aspirin, or anti-malarial drugs
o Neonates show hyperbilirubinemia and jaundice – increased bilirubin due to breakdown of RBCs.
o Anaemia, fatigue, pallor, breathlessness – haemolysis of RBCs.
o Jaundice – increased bilirubin due to breakdown of RBCs.
o Splenomegaly – increased removal of haptoglobin-haemoglobin complexes via RES macrophages.
o Dark coloured urine – excess haemoglobin is excreted in the urine.
What are the laboratory findings?
o Normal parameters when not in oxidative stress
o Anaemia – low RBC and low Hb
o Decreased MCV – decreased Hb
o Increased reticulocyte count
o Possible increased WBC if there is an infection causing the oxidative stress
o Blood film shows bite cells – RES macrophages bite the RBCs to remove the damaged Hb
o Blood film shows blister cells – damaged Hb contracts to one pole of the cell
o Blood film shows Heinz bodies in reticulocytes – oxidised denatured Hb
What further tests should be carried out?
o Biochemistry tests: LDH (increased), bilirubin (increased) and haptoglobin (decreased), urine bilirubin and haemoglobin (increased)
o Measure the rate of NADPH production
o G6PD screen
o Repeat all tests when WBC and reticulocyte count is normal (as these falsely raise G6PD levels)
How is G6PD deficiency treated?
o Removal of the oxidative stress trigger – e.g., antibiotics, aspirin
o Underlying cause treated – e.g., infection
o Transfusions
o Neonatal phototherapy and exchange transfusion
