Platelet Count Essentials: What You Need to Know for a Healthy Blood System

Platelets are anucleate disc shaped formed elements of the blood derived from bone marrow. Platelet counts are extremely commonly requested tests from hematology laboratories. Tremendous technological strides in the last few decades, especially the widespread use of hematology analysers, has revolutionised blood cell enumeration and size measurement.

The Platelet count:

A vital parameter

Abnormalities of the platelet count occur in myriad disease across virtually all specialties making it essential "baseline" test in modern medical practice.

Reference counts are in the range 1.5 lacs to 4.5 lacs per micro litre.

The results of platelet count are essential in clinical decision making especially in critical care medicine with the development of advanced treatment modalities with the potential to save far sicker patients than previously possible.

Highly reproducible and accurate reports are indispensable for modern trauma and intensive care units,oncology services administrating high dose chemotherapy, surgical departments and bone marrow or solid organ set ups.

Transfusion services have evolved in tandem and platelet transfusions whether pooled from multiple donors (RDP) or obtained from single donor (SDP) are routine treatments for severe symptomatic thrombocytopenia.

Platelet transfusions units are limited and expensive and transfusion services struggle with ever increasing demands. Improving platelet inventory management by eliminating unnecessary transfusions is a prime goal of therapy.

Defining laboratory and or clinical threshold for platelet transfusions in markedly thrombocytopenic patients is a recurring theme in literature.

It was estimated that lowering the transfusion trigger from 20000 to 10000 reduces the number of platelet units transfused by 20-30%thus underscoring the decisive role of a platelet count in that range.

Spurious platelet count on automated analyzers

1. Sampling related technical considerations
Collection in vials other than lavander top (EDTA) vials , prolonged draw times, inadequate mixing and vial overfilling cause low count due to clump formation.
Samples taken in proximity to an IV drip or the first sample from a line are likely to be diluted.

2. Edta induced platelet aggregation  
This refers to the in vitro formation platelet clumps in blood collected in EDTA tubes.
This occurs in 0.07 -0.2 percent routine samples
Remedial measures: Collection of blood in citrate or heparin vacutainer.

3. Large platelet 
Harris syndrome -Asymptomatic constitutional macrothrombocytopenia characterized by absence of bleeding , variable thromocytopenia and giant platelets  and normal platelet function in donors from West Bengal.

In summary

The platelet count is a vital investigation modern medicine.
Blood film estimates of platelet count are useful cross checks for cell counter platelet results.
Automated counter results may be influenced by multiple variables eg patient related factors, anticoagulant a, inappropriate collection techniques, extraneous substanceds and interference by red cells.

Also read,

What causes a Low Platelet Count in Humans?

What is Platelet Count and What are causes for Elevated Platelet Count?

Understanding Platelets and their Importance