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# Symptoms of low platelet counts

## Problem

Thrombocytopenia is the state of having few platelets in the blood. It is often defined by a platelet count below 50, comma, 000 platelets per microliter. One common symptom of thrombocytopenia is the presence of petechiae, which are small red or purple spots visible on the skin. Petechiae result from broken capillary vessels.
A researcher wants to find out at what platelet concentration petechiae begin to be seen. In order to do this, he measures the platelet concentration of 120 patients with low platelet levels and performs a physical examination to check for petechiae. He does not interfere with any element of their treatment, including for their thrombocytopenia.
The researcher then divides the patients into 5 groups according to platelet levels, as shown in the table below. He calculates the percentage of patients in each group who have petechiae.
Platelet count (platelets/µL)% of patients with petechiae
0-9, comma, 999 (n=16)81
10, comma, 000-19, comma, 999 (n=20)55
20, comma, 000-29, comma, 999 (n=26)12
30, comma, 000-39, comma, 999 (n=32)3
40, comma, 000-50, comma, 000 (n=26)4
What component of blood do platelets interact with to form a blood clot?