2% to 6%

0% to 5%


20% to 44%

48% to 78%


2% to 9%

2% to 11%


0% to 4%

1% to 4%


0% to 2%

0% to 2%

records concerning notification of a patient with a critical value. Date, time, and person receiving the information are usually recorded. For a list of sample critical values refer to Table 9.5.

Manual Differential Versus Differential Scan

Most automated hematology instruments have the capacity to perform a differential count. This advance in instrumentation has dramatically shifted work patterns, because less time is spent in reviewing peripheral smears. When a differential is ordered and reported from instrumentation, there are some conditions in which the automated differential count may be questionable. If certain parameters in the differential have been flagged or if a peripheral smear needs to be reviewed as a result of a delta check or reflex testing, the peripheral smear is actually reviewed by a laboratory professional. For these circumstances, there are two levels of technologist review: a manual leukocyte differential count or a differential scan. A manual leukocyte differential count implies that 100 WBCs are counted along with red cell morphology and platelets. A diff scan implies that approximately 50 cells are reviewed to

Table 9.4 O When to Consider Counting More Than 100 Cells on Differential*

• Blasts (first-time patient)

Table 9.2 O Leukocyte Counts at Different Ages*

Age Leukocyte Count

*These values will vary with every clinical site.

Table 9.5 O Sample Critical Values

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