Primary objective The objective of this study is to compare anti-Xa levels obtained with a standard high dose thrombosis prophylaxis in COVID-19 intensive care-patients compared with anti-Xa levels obtained with a normal dose thrombosis prophylaxis in non-COVID-19 intensive care patients.

Secondary objectives

1. To determine the incidence of anti Xa levels out of range of the established target anti Xa level in both groups.
2. To determine the influence of relevant co-variates on the anti-Xa level in the COVID-19 and non-COVID-19 group.

Inclusion Criteria:

• All COVID-19 patients > 18 years admitted at the ICU using nadroparin in a high thrombosis prophylactic dosage of 1 dd 5700 IU or 2 dd 5700 IU sc
• All medical non-COVID-19 patients admitted at the ICU using nadroparin in a standard prophylactic dosage of 1 dd 2850 IU sc.
• Minimum estimated length of stay on the ICU of 4 days

Exclusion Criteria:

o (History of) Heparin Induced Thrombocytopenia and Thrombosis

All adult ICU patients (COVID-19 and non-COVID-19 patients) using nadroparin with the intention of thrombosis prophylaxis are included. Anti Xa activity is determined once per patient at least 3 days (peak level after 4th administration) after admission at the ICU and on nadroparin treatment. No randomization.