Voluntary donors of SDPs were screened as per standard guidelines prior to the procedure. A complete blood count (including MPV) along with a peripheral blood smear, to assess the platelet morphology, was done. The study was conducted in Tata Medical Centre, Kolkata, India. A total of 45 donors were screened for plateletpheresis. Following plateletpheresis from these donors, a platelet count from the collection bag was done after 1 hour to estimate the platelet yield. The SDP was transfused as a single unit to the patient, as per clinical need. Platelet counts on patients were done after one hour and the platelet recovery was calculated according to the formula [6].

TBV = Total blood volume (75ml/kg for adults)

PCI = Platelet count increment (Platelet count after transfusion – Platelet count before transfusion)

Number of platelets transfused = Platelet yield (estimated from collection bag).

Out of the 45 donors who were screened, 30 (66.67%) were found to have giant platelets. [Table/Fig-1] shows that the pre procedure platelet counts in donors having giant platelets (peripheral smear showing giant platelets in [Table/Fig-2]; platelet histogram showing evidence of presence of giant platelets in [Table/Fig-3]) were relatively low (1.5 -1.8 lacs/cumm) and so also the platelet yield (2.6-3.2x10¹¹) compared to donors who did not, but the post transfusion platelet recovery was greater (44.4-99.29%); mean being 68.1 (SD = 13.39). In donors who did not have giant platelets, the platelet counts were in the range of 1.5 – 3.6 lacs/cumm, platelet yield was 3.1-3.8x10¹¹ and platelet recovery was 25.54-52.5%; mean being 40.79 (SD = 7.36) [Table/Fig-4]. Data is normally distributed as Shapiro-Wilk’s test is not significant (p-value >0.05). Applying independent sample t test, it is seen that there is significant difference in platelet recovery (p-value<0.05) in both the groups (donors with giant platelets versus donors with no giant platelets).

[Table/Fig-2]:

Peripheral blood smear of a blood donor showing giant platelets (Leishman, 1000x)

[Table/Fig-3]:

Platelet histogram of a blood donor showing presence of giant platelets

Therefore, it was observed that although the pre-donation platelet count and platelet yield in donors were on the lower range in donors who had giant platelets in them, the platelet recovery was greater compared to that from donors who did not have giant platelets.

Of all the inherited thrombocytopenias, Harris platelet syndrome (HPS) is the most common [4]. In 2002, this syndrome was called "Asymptomatic constitutional macro thrombocytopenia" (ACMT) [3]. In 2005, this entity was renamed as Harris platelet syndrome to avoid confusion between ACMT and congenital amegakaryocytic thrombocytopenia (CAMT) [4,5]. HPS was identified among healthy blood donors in the north-eastern part of the Indian subcontinent, characterized by absent bleeding symptoms, mild to severe thrombocytopenia (platelets rarely <50 X 10⁹/L)with giant platelets (Mean platelet volume 10fL) and normal platelet aggregation studies with absent MYH9 mutation [4]. Authors have found a statistically higher MPV, RDW and a lower platelet count and platelet biomass in the blood donors with HPS [3]. The present day diagnosis of HPS is based on ascertaining the ethnicity of the patient, as well as assessing for conditions causing acquired thrombocytopenias, and also excluding the known inherited giant platelet disorders (IGPD) and other congenital thrombocytopenias. It is extremely important to recognize and diagnose Harris platelet syndrome, as almost one third the population of certain parts of Indian subcontinent is affected [5,7].

Earlier studies have shown that larger platelets, as compared with smaller platelets, are more active enzymatically and metabolically and have a higher potential thrombotic ability [8]. It has also been shown that platelet size, when measured as mean platelet volume (MPV), is a marker of platelet function and is positively associated with indicators of platelet activity [8]. However, we currently lack understanding of the predictive accuracy of high MPV in SDP donors for post transfusion platelet recovery in patients. The index study shows that the platelet recovery was greater when patients were transfused with platelet units containing giant platelets. This could be an indicator that giant platelets are functionally more active than normal platelets. However, function of giant platelets need to be assessed by performing platelet function tests to establish this correlation. Future research works based on platelet function with a larger sample size are needed to clarify this issue.

It is recommened that a peripheral smear examination should always be done to verify the platelet counts given by auto-analyser, because in case of presence of giant platelets in donors the auto-analyser may give a false low count and relying on machine counts solely may lead to rejection of donors who actually might be having a platelet count >1.5 lacs per cumm. Therefore, in the Eastern part of India, a peripheral smear examination or platelet count in Neubauer’s chamber should be made an essential component for screening plateletpheresis donors. As the study noted that platelet recovery in patients was greater with transfusion of platelet units containing giant platelets, it might be suggested that plateletpheresis donors with platelet count lower than the eligibility cut-off of 1.5 lacs per cumm, but with presence of giant platelets may be accepted as SDP donors in the Eastern part of India. This, if possible, would add to the precious apheresis donor pool and contribute to the easier management of patients who are in dire need of platelets.