This meta-analysis found that individuals with either severe cases or non-surviving cases of COVID-19 had lower platelet counts compared to individuals with non-severe and surviving cases, suggesting that thrombocytopenia may be a risk factor for COVID-19 progressing into a more severe state. 

• From the search (including articles up to 30 April 2020), authors found 31 studies with 7613 participants.
• For the 25 studies reported the platelet count of both severe and non-severe COVID-19 patients, the pooled SMD revealed a lower platelet count in severe patients than non-severe patients (SMD=-0.36, 95% CI: -0.48~-0.23, I^2=56.9%)
• Six of the 25 studies defined death as the severe state. The pooled SMD revealed a much lower platelet count in non-survivor COVID-19 patients than survivor patients (SMD=-0.60, 95% CI: -0.72~-0.47, I^2<0.1%)
• Of note, abnormal platelet counts, especially thrombocytopenia, are common in the ICU and usually indicate organ dysfunction that lead to a disorder of homeostasis. Thus, it may not be a specific indicator for COVID-19 itself, but rather, of the overall worsening clinical status of a patient.