WBC/High-Power Field Estimated WBC Count
3. An alternative technique is to do a WBC estimate by taking the average number of white cells and multiplying by 2000.
Observations Under X100: Platelet Estimates
1. Platelet estimates are done under X 100 with the RBCs barely touching, approximately 200 RBCs. This takes place under the X 100 objective (oil). On average there are 8 to 20 platelets per field. See Table 20.2.
2. Ten fields are counted using the zigzag method. This method of counting is done by going back and forth lengthwise or sidewise (Fig. 20.8).
Platelets per oil immersion field (OIF) <8 platelets/OIF = decreased 8 to 20 platelets/OIF = adequate
>20 platelets/OIF = increased
3. After the 10 fields are counted, the number of platelets is divided by 10 to get the average. The average number is now multiplied by a factor of 20,000 for wedge preparations. For monolayer preparations, use a factor of 15,000.
Figure 20.8 Zigzag method of performing differential.
Example: 120 platelets/10 fields = 12 platelets per field
12 X 20,000 = 240,000 platelets
Manual Differential Counts
1. These counts are done in the same area as WBC and platelet estimates with the red cells barely touching.
2. This takes place under X100 (oil) using the zigzag method previously described in the platelet estimate (see Fig. 20.8).
3. Count 100 WBCs including all cell lines from immature to mature. Normal values for WBCs can be found in Table 20.3.
Observing and Recording Nucleated Red Blood Cells (nRBCs)
1. If nRBCs are observed while performing the differential, they need to be reported. These elements in a peripheral smear are indicative of increased erythropoietic activity and usually a pathologic condition. Additionally, the presence of nRBCs per 100 white cells will falsely elevate the white count and is clinically significant.
2. Correct the WBC count if the nRBC count is greater than 5 nRBCs/100. The following formula is applied for correcting NRBCs:
WBC X 100/NRBC + 100
Example : If WBC = 5000 and 10 NRBCs have been counted
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