PF4 and acute kidney injury: The association between PF4 test positivity and severe AKI was similar across each of the following subgroups: age (≥65 versus <65 years; P = 0.11 for interaction), baseline eGFR (<60 versus ≥60 ml/min per 1.73 m2; P = 0.09 for interaction), platelet count (>100, 50–100, <50 K/μl; P = 0.80 for interaction), invasive mechanical ventilation (P = 0.36 for interaction), sepsis (P = 0.54 for interaction), and shock (P = 0.72 for interaction).