Osmotic Fragility Test Flashcards

*Question: What does the Osmotic Fragility Test (OFT) primarily measure?
A) The ability of RBCs to carry oxygen
B) The ability of RBCs to take up fluid without being destroyed
C) The hemoglobin concentration within RBCs
D) The rate of RBC production in bone marrow

*Answer: B) The ability of RBCs to take up fluid without being destroyed

*Question: What is the primary factor affecting the result of the Osmotic Fragility Test?
A) Hemoglobin type and concentration
B) RBC count and reticulocyte index
C) RBC shape and surface area-to-volume ratio
D) Plasma osmolality and pH

*Answer: C) RBC shape and surface area-to-volume ratio

*Question: Why are hypotonic solutions used in OFT instead of hypertonic solutions?
A) Hypertonic solutions destroy the cell membrane chemically
B) Hypertonic solutions cause crenation, not hemolysis, so fragility cannot be tested
C) Hypotonic solutions stabilize RBC shape for easier visualization
D) Hypertonic solutions interfere with spectrophotometric readings

*Answer: B) Hypertonic solutions cause crenation, not hemolysis, so fragility cannot be tested

*Question: At what NaCl concentration do normal RBCs show INITIAL hemolysis?
A) 0.85%
B) 0.60%
C) 0.50%
D) 0.30%

*Answer: C) 0.50%

*Question: At what NaCl concentration is COMPLETE hemolysis expected in normal RBCs?
A) 0.50%
B) 0.45%
C) 0.40%
D) 0.30–0.35%

*Answer: D) 0.30–0.35%

*Question: What is the isotonic concentration used as the reference in OFT?
A) 0.45% NaCl
B) 0.65% NaCl
C) 0.85% NaCl
D) 1.00% NaCl

*Answer: C) 0.85% NaCl

*Question: What happens to RBCs in a hypotonic solution?
A) They shrink due to water leaving the cell
B) They remain unchanged due to osmotic equilibrium
C) They swell due to water entering the cell and may lyse
D) They become crenated and more resistant to hemolysis

*Answer: C) They swell due to water entering the cell and may lyse

*Question: Which direction does the osmotic fragility curve shift in Hereditary Spherocytosis?
A) Rightward shift
B) No shift
C) Leftward shift
D) Bimodal shift

*Answer: C) Leftward shift

*Question: A leftward shift of the OFT curve indicates what?
A) Decreased osmotic fragility
B) Increased osmotic fragility
C) Normal osmotic fragility
D) Bimodal cell population

*Answer: B) Increased osmotic fragility

*Question: Which condition is associated with a RIGHTWARD shift of the OFT curve?
A) Hereditary Spherocytosis
B) Immune hemolytic anemia
C) Thalassemia
D) Thermal RBC injury

*Answer: C) Thalassemia

*Question: Why do spherocytes have increased osmotic fragility?
A) They have excess surface membrane that ruptures easily
B) They have a decreased surface area-to-volume ratio and limited capacity to accommodate water influx
C) They lack hemoglobin to maintain membrane stability
D) They have an abnormally high intracellular osmolarity

*Answer: B) They have a decreased surface area-to-volume ratio and limited capacity to accommodate water influx

*Question: What anticoagulant is used in the Osmotic Fragility Test?
A) EDTA
B) Sodium citrate
C) Heparin
D) Oxalate

*Answer: C) Heparin

*Question: How much blood is added to each tube in the OFT procedure?
A) 0.10 mL (100 µL)
B) 0.04 mL (40 µL)
C) 0.02 mL (20 µL)
D) 0.50 mL (500 µL)

*Answer: B) 0.04 mL (40 µL)

*Question: What blood-to-solution ratio is maintained in the OFT?
A) 1:10
B) 1:50
C) 1:100
D) 1:200

*Answer: C) 1:100

*Question: What is the total volume of solution in each OFT tube?
A) 1 mL
B) 2 mL
C) 4 mL
D) 10 mL

*Answer: C) 4 mL

*Question: How long are the OFT tubes incubated and at what temperature?
A) 15 minutes at 37°C
B) 30 minutes at room temperature
C) 60 minutes at 4°C
D) 45 minutes at 37°C

*Answer: B) 30 minutes at room temperature

*Question: At what speed and duration are OFT tubes centrifuged?
A) 1,000 rpm for 10 minutes
B) 3,000 rpm for 3 minutes
C) 2,000 rpm for 5 minutes
D) 500 rpm for 15 minutes

*Answer: C) 2,000 rpm for 5 minutes

*Question: At what wavelength is the supernatant read spectrophotometrically in OFT?
A) 450 nm
B) 490 nm
C) 520 nm
D) 540 nm

*Answer: D) 540 nm

*Question: What does the spectrophotometric reading of the supernatant measure after centrifugation?
A) NaCl concentration remaining in solution
B) Hemoglobin released due to hemolysis
C) RBC count in the supernatant
D) Osmolality of the solution

*Answer: B) Hemoglobin released due to hemolysis

*Question: In the % Hemolysis formula, what does A0.0% represent?
A) Absorbance at isotonic saline (baseline)
B) Absorbance at the tube being tested
C) Absorbance at 0% NaCl (complete lysis reference)
D) Absorbance at 0.45% NaCl (normal lysis point)

*Answer: C) Absorbance at 0% NaCl (complete lysis reference)

*Question: What is the correct formula for calculating % hemolysis in OFT?
A) (A0.85% − Ax%) ÷ (A0.0% − Ax%) × 100
B) (Ax% − A0.0%) ÷ (A0.85% − A0.0%) × 100
C) (Ax% − A0.85%) ÷ (A0.0% − A0.85%) × 100
D) (A0.0% − A0.85%) ÷ (Ax% − A0.85%) × 100

*Answer: C) (Ax% − A0.85%) ÷ (A0.0% − A0.85%) × 100

*Question: What is plotted on the X-axis of the osmotic fragility curve?
A) Percent hemolysis
B) Absorbance at 540 nm
C) Percent NaCl concentration
D) Time of incubation

*Answer: C) Percent NaCl concentration

*Question: What is plotted on the Y-axis of the osmotic fragility curve?
A) NaCl concentration
B) Percent hemolysis
C) Absorbance values
D) Surface area-to-volume ratio

*Answer: B) Percent hemolysis

*Question: What is the major drawback of the Osmotic Fragility Test?
A) It requires expensive and specialized equipment
B) It cannot detect any form of hemolytic anemia
C) It lacks sensitivity and may miss mild cases of Hereditary Spherocytosis
D) It cannot be performed on heparinized blood

*Answer: C) It lacks sensitivity and may miss mild cases of Hereditary Spherocytosis

*Question: OFT is described as a nonspecific test because:
A) It cannot detect any RBC abnormality
B) Increased fragility does not differentiate HS from other causes of spherocytosis such as burns or immune hemolytic anemia
C) It only works for thalassemia patients
D) Results vary greatly between laboratories

*Answer: B) Increased fragility does not differentiate HS from other causes of spherocytosis such as burns or immune hemolytic anemia

*Question: Which of the following will cause a FALSE POSITIVE (increased fragility) result in OFT?
A) Using heparinized blood
B) Incubating tubes for exactly 30 minutes
C) Rough handling of tubes causing mechanical lysis
D) Centrifuging at 2,000 rpm

*Answer: C) Rough handling of tubes causing mechanical lysis

*Question: Why are tubes covered with parafilm during OFT?
A) To maintain temperature during incubation
B) To prevent evaporation and contamination of solution
C) To block light exposure from affecting hemoglobin
D) To maintain NaCl concentration stability

*Answer: B) To prevent evaporation and contamination of solution

*Question: Which RBC morphology is specifically detected by OFT due to its decreased surface area-to-volume ratio?
A) Target cells
B) Elliptocytes
C) Spherocytes
D) Schistocytes

*Answer: C) Spherocytes

*Question: In Hereditary Spherocytosis, at what NaCl concentration does initial hemolysis occur?
A) 0.85%
B) 0.50%
C) Greater than 0.50% (e.g., 0.60%)
D) 0.30%

*Answer: C) Greater than 0.50% (e.g., 0.60%)

*Question: What does the "TAIL" on the osmotic fragility curve of Hereditary Spherocytosis represent?
A) Normal biconcave RBCs that resist lysis
B) RBCs with extreme fragility after conditioning in the spleen
C) Reticulocytes that are more resistant to hemolysis
D) Target cells from a concurrent thalassemia

*Answer: B) RBCs with extreme fragility after conditioning in the spleen

*Question: A patient's OFT curve shows TWO populations — one with increased fragility and one with decreased fragility. What condition does this suggest?
A) Hereditary Spherocytosis
B) Immune hemolytic anemia
C) Thalassemia
D) Iron deficiency anemia

*Answer: C) Thalassemia

*Question: Why do target cells (as in thalassemia) show DECREASED osmotic fragility?
A) They have a reduced surface area-to-volume ratio
B) They have an increased surface area-to-volume ratio and more membrane capacity
C) They lack hemoglobin and are therefore lighter
D) They are larger than normal RBCs and resist water influx

*Answer: B) They have an increased surface area-to-volume ratio and more membrane capacity

*Question: What is the principle of osmosis as it applies to OFT?
A) Movement of solutes from low to high concentration
B) Movement of water from high solute concentration to low solute concentration
C) Movement of water from low solute concentration to high solute concentration
D) Movement of RBCs across a semipermeable membrane

*Answer: C) Movement of water from low solute concentration to high solute concentration

*Question: In which tube of the OFT setup is NO hemolysis expected in a normal patient?
A) Tube containing 0.00% NaCl
B) Tube containing 0.10% NaCl
C) Tube containing 0.85% NaCl
D) Tube containing 0.40% NaCl

*Answer: C) Tube containing 0.85% NaCl

*Question: Which of the following conditions can cause INCREASED osmotic fragility aside from Hereditary Spherocytosis?
A) Iron deficiency anemia
B) Thalassemia
C) Thermal RBC injury (burns) and immune hemolytic anemias
D) Megaloblastic anemia

*Answer: C) Thermal RBC injury (burns) and immune hemolytic anemias

*Question: What is the reference textbook cited for the OFT procedure?
A) Williams Hematology, 9th edition
B) Rodak's Hematology, 6th edition, Chapter 21
C) Harmening's Clinical Hematology, 5th edition
D) Henry's Clinical Diagnosis, 23rd edition

*Answer: B) Rodak's Hematology, 6th edition, Chapter 21

*Question: Which statement best describes why RBCs appear normal in isotonic saline?
A) Isotonic saline causes slight swelling that restores the biconcave shape
B) There is no net movement of water because intracellular and extracellular osmolarity are equal
C) Isotonic saline has a higher solute concentration that stabilizes the RBC membrane
D) RBCs actively transport water out to maintain shape in isotonic conditions

*Answer: B) There is no net movement of water because intracellular and extracellular osmolarity are equal

*Question: A normal OFT result in a patient suspected of having Hereditary Spherocytosis means:
A) The diagnosis of HS is definitively ruled out
B) The patient has thalassemia instead
C) HS cannot be excluded, especially in mild cases, due to OFT's lack of sensitivity
D) The patient's RBCs have a normal surface area-to-volume ratio

*Answer: C) HS cannot be excluded, especially in mild cases, due to OFT's lack of sensitivity

*Question: What shape do RBCs become as they swell in increasingly hypotonic solutions?
A) Elliptical
B) Crenated (star-shaped)
C) Spherical
D) Fragmented (schistocytes)

*Answer: C) Spherical

*Question: Which of the following best explains why OFT is considered an obsolete procedure?
A) It has been replaced by peripheral blood smear only
B) It lacks sensitivity and specificity, making it unreliable as a standalone diagnostic tool
C) It requires blood volumes too large to collect from patients
D) Modern labs no longer use NaCl solutions

*Answer: B) It lacks sensitivity and specificity, making it unreliable as a standalone diagnostic tool