Thank you for your reply.
I doubt that your platelet number was 21 because that is extremely low, not just borderline low. Usually when platelets are low it means that your blood is too thin and you would bruise easier and bleed more (however, not if the number is ***** borderline low, at border line low number you would not have any problems).
On the other hand Coagulated blood means that it thickens up and forms a clot which is completely opposite from having low platelets.
I still have a suspicion that the reason that your blood coagulated was an improper collection of blood (either incorrect stick, or bad test tube, or the test tube set for too long before being tested). The fact that it happened 3 times and in 2 different laboratories is a bit strange, however in March your blood work was normal (except for slightly low platelets).
There are a lot of different blood disorders which is why you are being referred to a hematologist. Most likely you will be just fine, however, a hematologist (who is a specialist in blood disorders, not only in cancer treatment) might order a set of very unique blood tests which are only known and understood by a hematologist for further evaluation.
At this point I would say that you do not need to worry so much. You will need to have some more blood work done (hopefully in the hematologist's office) for further evaluation. I do not think you are being referred to a hematologist/oncologist on the suspicion of cancer. If anything, he will be evaluating why your blood appears too thick.
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Best wishes and good luck,