Practical Flashcards
What is the erythrocyte sedimentation rate?
Definition:
It is the rate of sedimentation of RBCs in anticoagulated blood kept in a vertical narrow tube. RBCs sedimented to the
bottom of the tube, leaving a layer of clear plasma above it.
Why do the RBCs sediment?
The RBCs sediment because their density is greater than that of plasma; this is particularly
so, when there is an alteration in the distribution of negative charges on the surface
of the RBC (which normally keeps them separate form each other) resulting in their gathering to form large aggregates known as rouleaux
What are the determinants of ESR?
1) Plasma proteins:
- Increased globulins or fibrinogen…helps rouleaux
formation and increases ESR
-Decreased globulins or fibrinogen….. decreases ESR
- Decreased albumin….. helps rouleaux formation
2)Viscosity:
Increased viscosity retards ESR, whereas decreased viscosity
enhances it.
↑ Temperature → ↓ viscosity→ ↑ ESR and vice versa.
3) RBCS count:
* Anemia ………..fast sedimentation… increased ESR
* Polycythemia …..slow sedimentation…decreased ESR
4) Shape of the RBCs:
- Normal biconcave shape of RBCs facilitates rouleaux formation.
- In sickle cell anemia and in
spherocytosis, the shape of the cells tends to prevent rouleaux formation and hence decreases ESR.
- In iron deficiency anemia, the microcytes resist rouleaux formation and sedimentation is retarded.
How is ESR determined?
Determination of ESR:
Westergren’s method
Requiremets:
1. Westergren’s tube:Graduated 0-200 mm from
above downwards.
2. Stand for westergren’s tube.
3. Timer or watch
Procedure:
1. Mix 2 ml of venous blood to 0.5 ml of 3.8% sodium citrate solution. This will give a blood : citrate ratio of 4 : 1
- Fill the Westergren’s pipette with blood - citrate mixture by sucking till bringing the
blood column to exact zero mark. - Transfer it to the Westergren’s stand and press its lower end firmly into the rubber cushion, then slit the upper end of the pipette under the screw cap. Confirm that there’s no
leakage of blood. - Leave the pipette for one hour & then calculate the ESR by measuring the distance between the top of the plasma and the top of the sedimented red blood cells.
Express your results as: ……….. mm/h
How is the test performed?
Take a tube
Fill with blood
Leave it for an hour
Sedimentation occurs
* N.B: ESR can be calculated after 2 hours using the following equation:
Reading of 1st hour + ½ reading of 2nd hour
What are the normal values for male and female
Normal values:
✔ Males: 4-6 mm/h
✔ Female : 8-10 mm/h.
What are the factors affecting ESR?
Increase ESR:
Physiological: Females during pregnancy, menstruation and lactation
Pathological: Infection, Inflammation, malignancy, fractures (elevated gamma globulins or fibrinogen)
Decrease ESR:
Polycythemia
Low protein: fibrinogen or gamma-globulins
Spherocytosis
Sickle cell
What is the clinical significance of ESR?
- Many factors affect the ESR making it extremely non-specific.
- So, ESR is not diagnostic
but it is prognostic - That helps in monitoring disease activity or
response to therapy
What is RBC fragility?
RBCs fragility is the lack of resistance of RBCs to hemolysis when exposed to hypotonic
saline solutions (osmotic fragility) or when subjected to mechanical trauma (mechanical
fragility).
Normally, the RBC has high surface area to volume ratio (due to its biconcave shape) which allows it to increase in volume before being rupture when placed in hypotonic saline, but spherical RBCs hemolyze easily because of low surface area to volume ratio.
What is osmotic fragility?
Osmotic fragility: is a test to detect red blood cells that are more fragile than normal.
It is determined by placing RBCs in hypotonic NaCl solutions with different levels of dilution and
measuring the amount of hemolysis.
What is the method of determining osmotic fragility?
- Prepare a series of hypotonic solutions with NaCl content
ranging from distilled water to 0.8 %, to which a small amount of fresh heparinized blood is added. - After 30 min. of incubation followed by centrifugation, the
saline concentrations at which start of hemolysis and complete hemolysis occur are determined. - Start of hemolysis is determined by recording the pink coloration (hemoglobin color) of the supernatant.
- As the osmotic lysis progressively increases, the
supernatant color gradually darken from pink to red till
complete hemolysis is reached and the red color of the
supernatant is fixed.
What are the normal values for this test?
Normally red blood cells begin to hemolyze at 0.48% saline, 50% lysis occur at 0.4-0.42 and lysis completed at 0.35% saline
What is the significance of this test?
To detect hereditary spherocytosis (hemolysis starts at 0.7% and completed
at 0.5% saline solution
What are the causes of RBC hemolysis?
corpuscular:
-Defect in cell
wall (congenital
spherocytosis)
-Defect in Hb
(sickle cell anemia)
extra corpuscular:
-drugs
-Chemical poisons
-infections
-Antibodies against Rbcs
as incompatible blood
transfusion)
