- Assessment of platelet numbers: Platelet count and estimate.
- Assessment of platelet size: Mean platelet volume.
- Platelet morphologic features: This does not have its own category in a hemogram, but a comment is added if abnormalities in platelet features are observed
Platelet countPlatelet counts can be done manually using a hemocytometer or with an automated analyzer. Counts can also be estimated during blood smear examination. Since many laboratories use instruments that count platelets, RBC and WBC concurrently, a platelet count is a routinely reported result on complete or automatd hemograms. At Cornell University, all platelet counts from our analyzer are verified by examining a blood smear for platelet clumps (which will falsely lower the count) and estimating a platelet count from the monolayer (as needed). Sometimes, the platelet count from our machine is deemed inaccurate and the count is deleted, with an estimate provided instead (if do-able).
Platelet estimateIn a well-prepared smear, platelets are estimated by counting the average number of platelets seen per 100x oil immersion field in the monolayer. In general, 10 oil immersion fields are counted and the results averaged (this accounts for uneven dispersal of platelets in the smear). Then the following formula is applied:
Estimated platelet count/µL = average count in 10 fields x 15,000.At Cornell University, we provide a semi-quantitative estimate of platelet numbers which are based on reference intervals for the species in question (if available) as follows:
- Increased (Incr.): The count is above the reference interval for the species.
- Adequate (Adeq.): The count is within the reference interval for the species.
- Low?: The count is within the low end of the reference interval for the species or may be mildly decreased (i.e. the count is "equivocally low").
- Low: The count is below the reference interval for the species.
- Very low: The platelet count is below a medical decision limit associated with spontaneous hemorrhage, i.e. <30,000/uL.