Automated platelet counting--a re-evaluation of the sedimentation method

Area of Science:

• Hematology
• Laboratory Medicine
• Clinical Pathology

Background:

• Interlaboratory quality assessment surveys highlight discrepancies in platelet counting.
• The Coulter Thrombocounter with Thrombofuge method is widely used for platelet enumeration.

Purpose of the Study:

• To identify the causes of discrepancies in platelet counts obtained using the Coulter Thrombocounter with Thrombofuge method.
• To evaluate the accuracy, precision, drift, and carry-over of the Thrombocounter method.

Main Methods:

• Evaluation of the Coulter Thrombocounter using the Thrombofuge method for specimen preparation.
• Assessment of accuracy, precision, drift, and carry-over.
• Comparison with a whole blood reference method.

Main Results:

• Discrepancies in platelet counts were observed during routine use.
• The level of the sedimented plasma layer significantly contributed to errors.
• Strict adherence to manufacturer's instructions improved results, making them comparable to the reference method.
• The Thrombofuge method tended to yield higher platelet counts than the reference method for counts exceeding 200 X 10(9)/l, independent of other factors.

Conclusions:

• The sedimented plasma layer is a critical factor influencing platelet count accuracy with the Thrombofuge method.
• Standardized use according to manufacturer guidelines generally ensures reliable platelet counts.
• A systematic overestimation of platelet counts above 200 X 10(9)/l may occur with this method.