Interpretation of Results
A normal white count is 5,000-10,000/mm3. An increased white count is referred to as leukocytosis and can be seen in many pathological and sometimes non-pathological conditions. Conditions associated with a leukocytosis include:
1. Bacterial infections
2. Leukemia
3. Pregnancy
4. Newborn
A decreased white count is referred to as a leukopenia and can be seen in:
1. Viral infections
2. Lupus erythematosus
3. Overwhelming bacterial infections
4. Pernicious anemia
Sources of Error
Errors in hemocytometry most frequently arise as a result of:
1. Apparatus
2. Personal technique
3. Inherent error
(1) Errors caused by apparatus:
1. Chipped pipette tips
2. Obscure markings on pipettes
3. Non-optically plane cover glasses
4. Dirty glassware
5. Inaccurate rulings on chamber
(2) Errors caused by personal technique:
1. Not thoroughly mixing blood
2. Inadequate shaking
3. Failure to discard first 4 drops
4. Not loading chamber properly (overfilling, trapped air bubbles)
5. Counting cells inaccurately (skipping cells, counting cells twice, counting on wrong borders)
6. Calculation error
7. Clerical error
(3) Inherent errors in hemocytometry include:
1. "Field errors" - relates to the random distribution of cells on the counting chamber
2. Statistical error - occurs when total number of cells is too low to give statistical confidence in result (this error is reduced when larger numbers of cells are counted)