Q.Blood smear is used to study

Step 1. A blood smear is a thin film of blood spread on a slide, stained, and examined under the microscope so individual cells can be seen clearly.

Step 2. Total RBC (option a) and total WBC (option b) counts are obtained separately, using a haemocytometer with the appropriate diluting fluid (Hayem's fluid for RBC, Turk's solution for WBC) - not from a smear.

Step 3. Haemoglobin (option c) is measured with a haemoglobinometer, a different technique entirely, not by examining a stained smear.

Step 4. The specific purpose of a blood smear is to examine a well-stained peripheral smear and identify each type of white blood cell present, expressing each as a percentage of the total counted - this is the differential WBC count.

Recall that the smear technique's defining use is cell-type identification (the differential count), distinct from the numeric total counts done with a haemocytometer.

• Assuming a blood smear gives a total RBC or WBC count, which actually comes from haemocytometer counting, not the smear.
• Confusing haemoglobin estimation (a separate chemical test) with the microscopic cell-typing done on a smear.