OFT Flashcards
is a moasure of the abily of
the red cells to take up fluid without being destroyed.
osmotic fragility test (OFT)
It demonstrates increased fragility of red cells with decreased
surface area-to-volume ratio
OFT
OFT is a tost to help in the diagnosis of anemia, particularly of___origin.
hemolytic
• The primary factor aflecting the OFT is the________ &_________
shape of the red blood cells and its
surfaco area-to-volume ratio
Blood is added to a series of tubes with increasingly________
hypotonic sodium chloride solutions
In each tube, water either enters or leaves the red cells until…
equilibrium is achieved
In 0.85% NaCl…. (exolsin osmolarity)
the amount of water entering the cell is equivalent to the water leaving the cell because the intracellular and extracellular osmolarity is the same.
NORMAL BICONCAVE
• RBCs show initial hemolysis at_____
• Complete hemolysis generally occurs between______&______
0.45% NaCl
0.35% and 0.30% NaCl
• CURVE(Shifted to the______)
• Increased osmotic fragility with initial hemolysis at a NaCl concentration greater than 0.5%
LEFT
• CURVE (Shifted to the_____)
• decreased OFT
RIGHT
The Osmotic Fragility Test (OFT) is a laboratory test used to assess….
how well red blood cells (RBCs) can withstand swelling before they break (hemolyze).
This test evaluates the stability of_____ when exposed to varying concentrations of sodium chloride (NaCl) solution.
RBC membranes
• RBCs with a low surface area-to-volume ratio (e.g.,______) are more fragile and rupture easily in less dilute solutions.
• RBCs with an increased surface area-to-volume ratio (e.g.,_____) are more resistant and can tolerate more swelling before bursting.
spherocytes
target cells
The OFT helps in diagnosing hemolytic anemias, especially those caused by membrane defects, such as:
• Hereditary spherocytosis (increased fragility due to loss of membrane)
•bHereditary elliptocytosis (mildly increased fragility)
• Thalassemia (decreased fragility due to target cells)
Blood Sample Preparation
• A small amount of whole blood is added to a series of test tubes containing different concentrations of sodium chloride (NaCl) solution, ranging from_______-________
0.85% (isotonic) to 0.1% (highly hypotonic).
In isotonic solution (0.85% NaCl):
• The osmolarity (solute concentration) inside and outside the RBCs is the same.
• Water moves in and out of the cells at equal rates, maintaining normal cell shape.
Hereditary Spherocytosis (HS)
• RBCs are spherocytes (round, without the normal biconcave shape).
• They have less membrane surface area, meaning they cannot expand as much before bursting.
• Even in mild hypotonic solutions, they quickly take in water and hemolyze.
A____ shift of the curve indicates decreased osmotic fragility, meaning that RBCs resist hemolysis even in highly hypotonic solutions.
rightward shift
Key Findings
• RBCs take longer to hemolyze and do so at a lower NaCl concentration than normal.
• Initial hemolysis occurs at a lower-than-normal NaCl concentration.
Rightward shift
How the OFT is Performed
- Blood Sample Preparation
• A standard volume of fresh,______ blood is used to prevent clotting. - Testing with Different NaCl Concentrations
• The blood is added to a series of test tubes containing NaCl solutions ranging from____ to____
• The concentration of NaCl decreases in increments (e.g., 0.05% or 0.1% per tube).
heparinized
0.85% (isotonic) to 0.0% (distilled water).
- Incubation and Centrifugation
• The tubes are incubated at____ temperature for_____.
• After incubation, they are____ to separate the intact RBCs (pellet) from the free hemoglobin in the supernatant (plasma portion).- Measuring Hemolysis
• The absorbance of the supernatant is measured using a spectrophotometer at____ (to detect hemoglobin release).
- Measuring Hemolysis
room temp
30 minutes
centrifuged
540 nm
• ____= Absorbance in the test tube being measured.
• ____= Absorbance in the 0.85% NaCl tube (no hemolysis control).
• ____= Absorbance in the 0.0% NaCl tube (complete hemolysis control).
Aₓ%
A₀.₈₅%
A₀.₀%
Plotting the______
• The percentage of hemolysis is plotted against NaCl concentration to create an osmotic fragility curve.
• This curve helps determine whether RBCs lyse earlier or later than normal.
Osmotic Fragility Curve
Left shift conditions
• Hereditary spherocytosis (HS)
• Autoimmune hemolytic anemia (AIHA)
• Severe burns (thermal RBC injury)
Right shift conditions
• Thalassemia (target cells present)
• Liver disease (causing target cells)
• Iron deficiency anemia
