Aim To evaluate the prognostic value of baseline SOFA coagulation score (SOFA-CS) and change in platelet counts in patients with severe acute kidney injury (AKI) requiring continuous renal replacement therapy (CRRT). Methods We performed a secondary analysis from the Randomized Evaluation of Normal versus Augmented Level of RRT (RENAL) study. The primary endpoint was all-cause mortality at 90 days after randomization. The association between baseline SOFA-CS, changes in platelet counts, process of care, and clinical outcomes were analyzed using multivariate Cox model adjusted for baseline variables. Results The complete SOFA-CS data were available in 1454 out of 1508 patients from the RENAL study. Among them, 708 patients had an abnormal SOFA-CS (defined as SOFA-CS >= 1), while 746 patients had normal SOFA-CS at baseline (SOFA-CS = 0). An abnormal SOFA-CS was independently associated with an increased risk of death at 90 days (HR = 1.27, 95% CI = 1.05-1.53, P = 0.015). An abnormal SOFA-CS was associated with prolonged length of ICU stay and duration of mechanical ventilation as well. Furthermore, there was no significant association between changes in platelet counts in patients who survived beyond 4 days and 90 day mortality (HR = 1.26, 95% CI = 0.29-5.56, P = 0.76). However, on multivariable analysis a decline of >= 60% (HR = 1.93, 95% CI = 1.23-3.05, P = 0.004) was associated with 90 day mortality in patients who survived beyond the first 4 days. Conclusions In the RENAL study, thrombocytopaenia is a common phenomenon in patients with severe AKI receiving CRRT. An abnormal baseline SOFA-CS and reductions in platelet counts were associated with increased mortality at 90 days.