Platelet Count Estimation using Unstained and Stained Peripheral Blood Smears: A Comparative Study

Abstract

Introduction: The manual count of platelets using stained smears is the most commonly employed method, although this method has its own limitations. Hence, we planned to use unstained peripheral blood smear for platelet count estimation which is comparatively less time consuming to assess whether it can be used to detect the platelet count in emergency situations like dengue period when workload is more. Aim: To compare the platelet count on unstained and stained peripheral blood smear and to compare the advantages and disadvantages of these two methods. Materials and Methods: The present comparative study was conducted in University College of Medical Sciences and Guru Teg Bahadur Hospital, Delhi, in August and September 2016. Platelet counts were estimated in 500 cases on unstained smears using light microscope under 100X objectives without immersion oil. Condenser of microscope was lowered and iris diaphragm was closed to reduce illumination. Platelets were counted in 10 fields and area was marked. The same smear was stained using ‘Wright stain’ and examined using oil immersion. Average number of platelets in 10 fields was multiplied by 20,000 in both the methods to get platelet count estimate per micro litre and results of both the methods were compared using Intra-class Correlation Coefficient (ICC). Results: A total of 500 cases were categorised into four classes based on average number of platelets per 10 fields under oil immersion on peripheral smears stained with Wright stain. The p-value and agreement between unstained and stained smear was assessed using ICC. Excellent agreement was noted in Class 1 (0.995) while in Class 4 it was average (0.511) with p-value less than 0.05. Conclusion: Platelet count estimation on unstained peripheral smears can bring down the need of stained peripheral smears and automated platelet counters to a good extent where workload is more and laboratory facilities are not easily available.

Keywords

• haemostasis
• peripheral smear
• wright stain