Hematology: Red Cell Membrane Defects

What is the principle of the osmostic fragility test?

tests the fragility of cells by placing them in a range of hypotonic to hypertonic solutions of NaCl and seeing when they lyse

What is the normal range for osmotic fragility?

0.35 - 0.5

What does an increased osmotic fragility test imply? give examples.

cells are more fragile

spherocytes, burn patients, OHS

What does a decreased osmotic fragility test imply? give examples.

cells are less fragile, tougher

Sickle cells, Target cells, DHS

Are red cell membrane defects and deficiencies congenital or aquired?

congenital

hereditary spherocytosis: autosomal dominant

hereditary elliptocytosis: autosomal dominant

OHS and DHS: autosomal dominant

hereditary pyropoikilocytosis: autosomal recessive

Which protein is responsible for the exoskeleton made up of filaments?

spectrin

What are the layers of the RBC?

inner: spectrin

middle: cholesterol, glycoprotein

outer: glycolipids, phospholipids

What are the 3 components that are responsible for stabilization of the RBC membrane?

1) protein 2.1= ankyrin

2) GP= glycophorin

3) Sp= spectrin

What is SA/V?

surface area to volume ratio

decreased when cell has more volume than surface area

increased when cell has more surface area than volume

What are the 3 deficiencies in hereditary spherocytosis?

deficiency in spectrin, ankyrin, and Band 3 deficiencies

How are spherocytes formed?

uncoupling between skeletal proteins and outer lipid bilayer. shedding of lipid bilayer in the form of microvesicles. central pallor is lost

Is the SA/V ratio increased or decreased in hereditary spherocytosis?

decreased (membrane lost=surface area lost, too much volume)

What are the clinical S/S of hereditary spherocytosis?

jaundice and splenomegaly, older patients may develop bile stones

**homozygous dominant may be lethal

What are the lab features of hereditary spherocytosis?

hgb

retics

MCV

MCHC

OF

Autohemolysis

hgb low

retics elevated

MCV decreased or normal

MCHC increased

OF increased (more fragile)

Autohemolysis abnormal, but corrects with glucose

Describe the autohemolysis test.

draw 2 clot tubes (with and without glucose)

check for hemolysis after 60 minutes

hemolysed= abnormal reaction, glucose should correct it by fortifying the cell membrane.

What is the test of choice for hereditary spherocytosis?

osmotic fragility (will be increased)

In the osmostic fragility test, which concentration is isotonic? All solutions below this concentration are considered hyper or hypotonic?

isotonic is 0.8%

anything less is hypotonic

What is the morphology in hereditary spherocytosis?

spherocytes, microspherocytes

What is the normal flow of the sodium/potassium pump? How does it change in hereditary stomatocytosis?

normal flow: sodium pumps out, potassium pumps in

HS: opposite

What 4 specialized tests can be performed to determine the exact protein defect of a red cell. Which is used to detect Band 3?

SDS-PAGE

ELISA

PCR

EMA (can detect Band 3)

Which membrane defects are vertical, horizontal, and both?

vertical: hereditary spherocytosis

horizontal: hereditary elliptocytosis

both: pyropoikilocytosis

What are the 3 defects/deficiencies in hereditary elliptocytosis?

*defective* spectrin chains

deficiency in Band 4.1

deficiency in glycophorin C

What is the SA/V ratio in hereditary elliptocytosis?

unchanged, nothing is removed from the cell (OF also normal)

What does the defect in spectrin chains of hereditary elliptocytosis cause?

skeletal disruption-- they become elliptical after traveling through microcirculation but still have a normal lifespan

What is the lifespan of RBCs in hereditary elliptocytosis?

normal

What are the clinical S/S of hereditary elliptocytosis (normal and severe)?

normal/most common form: none

severe form: jaundice, splenomegaly, severe anemia

What are the lab findings of hereditary elliptocytosis (normal and severe)?

normal: >25% elliptocytes, >12g/dL hgb, mildly elevated retic (4%), normal OF

severe: elliptocytes, poik, schistocytes, decreased hgb, elevated retic (up to 20%), increased OF

What is the treatment for hereditary elliptocytosis (normal and severe)?

normal: none

severe: splenectomy

What are the 2 deficiencies in pyropoikilocytosis?

deficiency in alpha spectrin and a mutant spectrin

How does the deficiency in alpha spectrin and mutant spectrin affect the cell membrane in hereditary pyropoikilocytosis?

causes skeletal lattice disruption and cell destabilization

What are the clinical S/S of hereditary pyropoikilocytosis?

at birth: jaundice, *hepatosplenomegaly*, anemia

later in life: bilirubin stones

What morphologies are present in hereditary pyropoikilocytosis?

elliptocytes, microspherocytes, schistocytes

What is the hemoglobin of hereditary pyropoikilocytosis?

decreased (it is hemolytic)

What specific test can be performed to determine if the patient has hereditary pyropoikilocytosis?

thermal stability test: one regular smear made, one made after incubating blood for 10 minutes at 46C and cells will look "melted"

What will the retic count, OF, and autohemolysis test be for hereditary pyropoikilocytosis?

retic elevated

OF increased

autohemolysis test is abnormal with NO correction with glucose

What do OHS and DHS stand for? What are some other names for the two?

OHS: overhydrated stomatocytosis (aka hereditary hydrocytosis, stomatocytosis)

DHS: dehydrated stomatocytosis (herediatary xerocytosis)

What is the deficiency in OHS?

deficiency of stomatin secondary to an unknown protein mutation

What is the permeability and resulting SA/V ratio for OHS?

Na and water into the cell = decreased SA/V ratio = too much volume = high OF (fragile)

What is the permeability and resulting SA/V ratio for DHS?

Loss of K and water out of the cell = increased SA/V ratio = to little volume = low OF (tough)

What are the clinical features of hereditary stomatocytosis?

mild to severe hemolytic anemia

periodic episodes of jaundice

What are the lab features of OHS?

hgb

retic

MCHC

MCV

hgb mild/mod decrease

retic mod increase

MCHC decreased

MCV may be increased

What is the morphology of OHS?

10-50% stomatocytes on peripheral smear

What are the lab features of DHS?

hgb

MCHC

MCV

hgb puddling

MCHC increase

MCV slightly increase

What is the morphology of DHS?

Target cells, hgb puddling

What is the therapy of DHS?

treat symptoms (fluids, transfusions)