To determine the clinical significance of variation in haematocrit (Ht) and haemoglobin (Hb) values before and after image-guided percutaneous core needle biopsies (PCNBs) and evaluate its clinical significance. This single-centre, retrospective study included all the patients who underwent image-guided PCNBs between November 2012 and September 2018. In total, 105 cases (56 male; 53.3%; mean age 72±8 years) were available for analysis. Biopsies included lesions of the liver, lung, kidney, bone, paravertebral and soft-tissue masses, peritoneal implantations, and retroperitoneal neoplasms. The study's primary outcome was to compare the pre- and post-procedural Ht and Hb values and to evaluate their clinical significance. A significant decrease of the mean Hb and Ht values was detected post-biopsy (12.79±1.85 g/dl versus 12.03±1.72 g/dl and 38.75±4.93% versus 36.49±4.73%; p<0.0001). A decrease in the Ht and/or Hb level was noted in 93/105 (88.6%) and 94/105 (89.5%) of the patients; respectively. Four minor bleeding complications were noted (4/105; 3.8%), which resolved without any further treatment. An >4% decrease in Ht value was noted in 17/105 cases (16.2%) and an Hb decrease of ≥1.5 mg/dl was noted in 10/105 cases (9.5%), all without any haemodynamic compromise. A moderate post-PCNB decrease in Ht and Hb values compared to baseline should be expected, but should not raise concerns regarding an ongoing bleeding event, if not correlated with haemodynamic and clinical signs of haemorrhage. Copyright © 2019 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.