Hematology Lab Practical I -Sources of Error

Sources of Error for Manual Counts
Errors caused by apparatus:
-chipped pipette tips
-non-optically plane cover glasses
-dirty chamber/coverglass
-inaccurate rulings on chamber
Sources of Error for Manual Counts
Errors caused by personal technique:
-not thoroughly mixing blood
-inadequate mixing of diluted specimen
-failure to discard first few drops
-counting cells inaccurately (skipping cells, counting cells twice, counting on wrong borders)
-not loading chamber properly (overfilling, trapped air bubbles)
-calculation error
-clerical error
Sources of Error for Manual Counts
Errors inherent in hemacytometry:
-"field errors" - relates to the random distribution of cells on the counting chamber
-statistical error-occurs when total number of cells is too low to give statistical confidence in results (this error is reduced when large numbers of cells are counted).
Sources of Error for Platelet Counting
-Light adjustment is critical. If the condenser is not lowered to reduce light intensity, the platelets will fade out.
-The counting chamber and cover glass must be extremely clean because bacteria and debris can be misinterpreted as platelets. This type of artifact is generally much more refractive than platelets.
-Clumping of platelets sometimes occurs, and if so the specimen must be recollected.
-General errors for manual cell counts....
Sources of Error in Hemoglobin Determination
-Spectrophotometer is not zeroed or calibrated properly
-Inadequate mixing of blood sample
-Dirty of scratched cuvettes
-Not waiting for complete color development
-Incorrectly calibrated pipettes
-Careless technique
-Lipemic blood, (use blank which contains 20uL of patient's plasma, and 5mL cyanmethemoglobin reagent) - plasma or serum is cloudy
-Resisting hemoglobins -resisting to red cell lysis
-Extremely high WBC count (centrifuge test mixture and read supernatant)-cloudy
-Extremely icteric sample -gold color in plasma or serum...liver problems, breakdown of hemoglobin.
Sources of Error in Hematocrit Determination
-Incomplete sealing of the hematocrit tubes decreases hematocrit
-Inadequate centrifugation of the hematocrit tubes or allowing the tubes to stand too long after the centrifuge as stopped-increases hematocrit
-Excess anticoagulant-causes RBC's to shrink, decreasing the hematocrit
-Inadequate mixing of blood