section 18 - hgb. op

Question 1

define hemoglobinopathy

Answer 1

a defective amino acid sequence in globin chain

Question 2

list the normal adult hgb, composition and ratios

Answer 2

• hgb A (alpha2 beta2): >95%
• hgb A2 (alpha2 delta2): ~2%
• hgb F (alpha2 gamma2): 1-2%

Question 3

describe hgb S
- defect
- consequences of hgb S

Answer 3

• beta chain defect at 6th glutamic acid substituted for valine
• at low O2 environments forms long, stiff, less soluble bundles that deform RBC

Question 4

how can hgb S result in infraction

Answer 4

occludes microvasculature (bundle and block)

Question 5

list the two main promoters of sickling

Answer 5

• hypoxia
• low pH - decreases O2 affinity

Question 6

describe why hgb S does not manifest until after 6 months of life

Answer 6

by six months hgb F will attempt to transfer to beta family hgb with defective beta chain

Question 7

describe vaso-occlussive crisis (VOC)

Answer 7

• sickle cell crisis
• inflammation via over expression of P-selectin (adhesion mediator) on endothelial cells and PLTs
• formed cellular clusters damage tissues

Question 8

how does VOC effect the spleen

Answer 8

can cause autosplenectomy via infarcts - plts attach to spleen

Question 9

describe lab findings of sickle cell anemia (homozygous)

Answer 9

• 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

Question 10

what test must be run to confirm hgb. op

Answer 10

hgb electrophoresis

Question 11

describe lab findings of sickle cell trait (heterozygous)

Answer 11

• generally asymptomatic
• occ sickling in extreme hypoxia
• norm rbc morph
• tube sol +
• 20-40% hgb S
• > 60% hgb A

Question 12

describe hgb C

Answer 12

• second most common hgb. op
• beta chain defect 6th glutamic acid swapped for lysine

Question 13

describe lab findings of hgb C disease

Answer 13

• hemolytic anemia
• target, crystal, envelope
• may become micro hypo anemia

Question 14

describe lab findings of hgb C trait

Answer 14

• asymptomatic
• confirmed on hgb electrophoresis

Question 15

describe hgb SC

Answer 15

• most common double heterozygous hgb structure
• amino acid subs on 2 globin chains
• resembles mild sickle cell disease

Question 16

describe lab findings of hgb SC

Answer 16

• mild to mod norm anemia
• few sickle cells
• elongated boat shape cells
• target
• SC crystals
• tube sol +
• no hgb A, Hgb S +, hgb C +

Question 17

list reagents of sickledex tube solubility test

Answer 17

• saponin: lyse rbc to create hgb soln
• sodium hydrosulphite: reducing agent
• buffers

Question 18

describe principle of sickledex tube solubility

Answer 18

when hgb S is reduced (deoxygenated) it crystallizes and creates cloudy red suspension while normal hgb remains clear

Question 19

list what can cause tub sol false pos

Answer 19

• hyperproteinemia
• hyperlipidemia
• polycythemia
• other abnormal hgb

Question 20

list what can cause tube sol test false negatives

Answer 20

• anemia <7g/dL hgb present
• low hgb S (infant/heterozygote)
• reagent deterioration (light sensitive)

Question 21

describe hgb electrophoresis principle

Answer 21

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

Question 22

describe hgb electrophoresis procedure

Answer 22

• hemolysate applied to end of strip at 8.4-8.6 pH
• hgb will migrate
• comigratory hgb needs diff media/pH to separate

Question 23

list other abnormal hgb

Answer 23

• D
• G
• o-arab
• D-Punjab
• C-Harlem
• E
• M

Question 24

how does hgb E differ from other hgb op

Answer 24

beta chain defect with decreased production making it a hgb. op and thal

Question 25

describe hgb M

Answer 25

• unstable hgb
• sub in alpha or beta chain
• iron not oxidized and prevents O2 binding
• pt hav 30-50% methemoglobin
• heinz bodies present