| Age | Bands/Stab (%) | Segs/Polys (%) | Eos (%) | Basos (%) | Lymphs (%) | Monos (%) | Metas (%) |
|---|---|---|---|---|---|---|---|
| Birth–1 wk | 10–18 | 32–62 | 0–2 | 0–1 | 26–36 | 0–6 | — |
| 1–2 wk | 8–16 | 19–49 | 0–4 | 0–0 | 38–46 | 0–9 | — |
| 2–4 wk | 7–15 | 14–34 | 0–3 | 0–0 | 43–53 | 0–9 | — |
| 4–8 wk | 7–13 | 15–35 | 0–3 | 0–1 | 41–71 | 0–7 | — |
| 2–6 mo | 5–11 | 15–35 | 0–3 | 0–1 | 42–72 | 0–6 | — |
| 6 mo–1 yr | 6–12 | 13–33 | 0–3 | 0–0 | 46–76 | 0–5 | — |
| 1–6 yr | 5–11 | 13–33 | 0–3 | 0–0 | 46–76 | 0–5 | — |
| 6–16 yr | 5–11 | 32–54 | 0–3 | 0–1 | 27–57 | 0–5 | — |
| 16–18 yr | 5–11 | 34–64 | 0–3 | 0–1 | 25–45 | 0–5 | — |
| >18 yr | 3–6 | 50–62 | 0–3 | 0–1 | 25–40 | 3–7 | 0–1 |
Bands/Stab, immature forms of neutrophils; Segs, segmented neutrophils; Polys, polymorphonuclear neutrophils; Eos, eosinophils; Basos, basophils; Lymphs, lymphocytes; Monos, monocytes; Metas, metamyelocytes.
The differential count alone has limited value; it must always be interpreted in relation to the WBC count. If the percentage of one type of cell is increased, it can be inferred that cells of that type are relatively more numerous than normal, but it is not known whether this reflects an actual increase in the (absolute) number of cells that are relatively increased or an absolute decrease in cells of another type. However, if the relative (percentage) values of the differential count and the total WBC count are both known, it is possible to calculate absolute values that are not subject to misinterpretation.
Historically, a differential count was done manually, but current hematology instruments do an automated differential count. The count is based on a combination of hydrodynamic focusing and fluorescent dyes in newer instrumentation. However, not all samples can be evaluated by automated methods. When a leukocyte count is extremely low or high, a manual count may be necessary. Extremely abnormal leukocytes, such as those in leukemia, also have to be counted by hand. The automated instrument has built-in quality control that senses abnormal cells and flags the differential. A microscopic count must then be done.
Subtopic(s):