Principle :
- One drop of blood is mixed with one drop of sodium metabisulfate reagent on a slide .
- if the erythrocytes contain hemoglobin S , they will become sickled –shaped .
Method :
- Place a small drop of blood on a slide .
- Add an equal amount of the reagent and mix carefully
- Cover it with a coverslip and make sure that there is no air bubbles .
- Place the slide in a petri -dish that has wet filter paper in the bottom .
- Wait 30 min before examining then Microscopic examination x40
- Note : when using a reducing reagent such as sodium metabisulfate it is not necessary to seal the preparation .
- Neg.result = the erythrocytes remain round
- Re-examine the slide after 30 further minutes then after 2 hours and after 24 hours .
- Pos.result = the erythrocytes become sickle-shaped often with spikes .
- It’s important to examine several parts of the preparation as sickling can occur more quickly in one part than in another .
False negative :
- Outdated reagent , concentration of S hemoglobin is low , patient have moderate to severe anemia
- The sickle test does not distinguish between sickle-cell anemia and sickle –cell trait .
- Whenever possible ,Hb- electrophoresis should be carried out to confirm a diagnosis of sickle cell disease .
Sickle Cells
Sickling Test
