A 50-year-old man on ICU is receiving CVVHDF for AKI secondary to sepsis. He is being anticoagulated with regional citrate. His latest bloods show: ionised calcium 0.85 mmol/L (normal 1.15-1.30), total calcium 2.95 mmol/L (normal 2.2-2.6), and a total-to-ionised calcium ratio of 3.5. What does this pattern suggest?