REPORTING PLATELET COUNTS IN DENGUE – MANUAL OR AUTOMATED ? Which is more reliable ?

 Platelets are the smallest type of blood cells. They are important in blood clotting. When bleeding occurs, the platelets swell, clump together, and form a sticky plug that helps stop the bleeding. If there are too few platelets, uncontrolled bleeding may be a problem.
In the current season, dengue is not the only cause of decrease in platelet counts. Other causes like malaria, other viral infections, Vitamin B12 and folate defiiency etc can also cause reduction in platelet counts. That said, dengue patients may also clinically present without any decrease in platelet counts.

It is well-known that thrombocytopenia ( reduction in platelet counts) is one of the critical parameters in patient management. Therefore, it is very important that laboratories assess platelet counts with utmost accuracy. The normal range of platelet count in a healthy adult individual is 150000 - 400000/μL. Babies and children have different reference ranges.compared to adults Therefore please check on the lab report for normal age wize reference range. A count of 1.5 lacs would be considered as normal in adults but would qualify as decreased count in a child.

Platelets can be counted either on automated machines( automated method) or on manual blood smear by pathologist.(manual method).

Generally hospitals and laboratories measure platelet counts on automated hematology analyzers- as .these are simple to use and give fast results.However, they suffer from a very big disadvantage. This disadvantage is based on the principle on which these machines work.The machines are programmed in such a manner that any blood particle falling within a predermined size range is counted as platelet and above this range is counted as red cell(RBC – which contains hemoglobin and is responsible for red colour of blood).Although this concept works well in majority of cases, but machine readings are seldom reliable , especially when platelet counts are below 30,000/ cmm. Giant platelets will be counted as RBCs and the machine will give a factitiously low reading of platelets. - Again , if the sample has not been properly mixed at the time of collection, platelets will stick and form clumps. Again the size of these clumps will be more than that of individual platelets and machine will count these as RBCs , thus give a falsely low platelet count. Also, if the sample is collected in a periphery and takes a lot of time to reach the main lab , by this time the platelets would have swelled up due to presence of additives in the blood tube, and not be counted in platelets.but as RBCs instead. (due to size factor)
So what is the solution, ?
All such cases, where platelets are reported low on analyzers, must be screened on peripheral smear by pathologist. Only on looking at the peripheral smear , will the pathologist be able to confirm whether the platelet counts are actually low or not.

Summary : The analyzer is reliable in majority of cases . However, for all cases with low platelets, manual screening by a pathologist is must for confirmation and to avoid unnecessary panic and unrequired platelet transfusions.