Subjects with severe renal impairment (eGFR ≤ 30 mL/min/1.73 m2) at risk of VTE secondary to non-surgical reasons and receiving thromboprophylactic doses of tinzaparin. The study sample will be selected from patients that are hospitalized by medical departments (i.e. nephrology, internal medicine, cardiology, pneumology) and on the transitional hospitalization unit.