section 18 - hgb. op Flashcards
define hemoglobinopathy
a defective amino acid sequence in globin chain
list the normal adult hgb, composition and ratios
- hgb A (alpha2 beta2): >95%
- hgb A2 (alpha2 delta2): ~2%
- hgb F (alpha2 gamma2): 1-2%
describe hgb S
- defect
- consequences of hgb S
- beta chain defect at 6th glutamic acid substituted for valine
- at low O2 environments forms long, stiff, less soluble bundles that deform RBC
how can hgb S result in infraction
occludes microvasculature (bundle and block)
list the two main promoters of sickling
- hypoxia
- low pH - decreases O2 affinity
describe why hgb S does not manifest until after 6 months of life
by six months hgb F will attempt to transfer to beta family hgb with defective beta chain
describe vaso-occlussive crisis (VOC)
- sickle cell crisis
- inflammation via over expression of P-selectin (adhesion mediator) on endothelial cells and PLTs
- formed cellular clusters damage tissues
how does VOC effect the spleen
can cause autosplenectomy via infarcts - plts attach to spleen
describe lab findings of sickle cell anemia (homozygous)
- sickle, target, baso stipp, HJ
- often neutrophilia/shift left
- often thrombocytosis
- BM erythroid hyperplasia
- tube sol test +
- hgb electropheresis: hgb S +, Hgb A =, inc Hgb F, norm hgb A2
what test must be run to confirm hgb. op
hgb electrophoresis
describe lab findings of sickle cell trait (heterozygous)
- generally asymptomatic
- occ sickling in extreme hypoxia
- norm rbc morph
- tube sol +
- 20-40% hgb S
- > 60% hgb A
describe hgb C
- second most common hgb. op
- beta chain defect 6th glutamic acid swapped for lysine
describe lab findings of hgb C disease
- hemolytic anemia
- target, crystal, envelope
- may become micro hypo anemia
describe lab findings of hgb C trait
- asymptomatic
- confirmed on hgb electrophoresis
describe hgb SC
- most common double heterozygous hgb structure
- amino acid subs on 2 globin chains
- resembles mild sickle cell disease
describe lab findings of hgb SC
- mild to mod norm anemia
- few sickle cells
- elongated boat shape cells
- target
- SC crystals
- tube sol +
- no hgb A, Hgb S +, hgb C +
list reagents of sickledex tube solubility test
- saponin: lyse rbc to create hgb soln
- sodium hydrosulphite: reducing agent
- buffers
describe principle of sickledex tube solubility
when hgb S is reduced (deoxygenated) it crystallizes and creates cloudy red suspension while normal hgb remains clear
list what can cause tub sol false pos
- hyperproteinemia
- hyperlipidemia
- polycythemia
- other abnormal hgb
list what can cause tube sol test false negatives
- anemia <7g/dL hgb present
- low hgb S (infant/heterozygote)
- reagent deterioration (light sensitive)
describe hgb electrophoresis principle
hgb carry electric charge based on amino acid composition and pH of medium. Each hgb has characteristic migration pattern based on amino acids that allow them to be differentiated
describe hgb electrophoresis procedure
- hemolysate applied to end of strip at 8.4-8.6 pH
- hgb will migrate
- comigratory hgb needs diff media/pH to separate
list other abnormal hgb
- D
- G
- o-arab
- D-Punjab
- C-Harlem
- E
- M
how does hgb E differ from other hgb op
beta chain defect with decreased production making it a hgb. op and thal
describe hgb M
- unstable hgb
- sub in alpha or beta chain
- iron not oxidized and prevents O2 binding
- pt hav 30-50% methemoglobin
- heinz bodies present
