Final answer:
To differentiate between WBCs, RBCs, and casts under a microscope, one must recognize the distinct morphology of WBCs with nuclei and RBCs without nuclei, like disc-shaped cells. Casts, which relate more to geological contexts, are solid replicas formed from molds. A systematic counting method can identify and classify cell types in a blood smear.
Step-by-step explanation:
Distinguishing a Clump of WBC or RBC from a Cast
When examining a blood smear under a microscope, it is vital to differentiate between white blood cells (WBCs), red blood cells (RBCs), and casts. The morphology of WBCs is distinct as they have nuclei and do not contain hemoglobin. They can be classified into granulocytes (neutrophils, eosinophils, and basophils) and agranulocytes (monocytes and lymphocytes). Each of these leukocyte types has a unique appearance after histologic staining which assists in their identification.
On the other hand, RBCs, which contain hemoglobin, lack a nucleus and appear as uniform, disc-shaped cells under the microscope. Clumps of these cells can be distinguished from each other and from casts, which are different. Casts are the result of impressions left in sediment by organisms that, when filled with new sediment, form a solid replica. This concept, while similar in name, is not typically related to hematological studies but is more common in geological contexts.
Differentiating between RBCs and WBCs, one should follow a systematic approach, such as using a grid method or constructing a simple table to classify and count the various cell types in a blood smear. This process often includes staining and examining the smear using an oil immersion lens to accurately identify and calculate cell percentages, which can indicate normal or abnormal conditions in a blood smear.