The most common complication preventing outpatient management after percutaneous CT-guided lung biopsy (PTLB) is the occurrence of pneumothorax requiring drainage. We previously developed a pragmatic score to predict the risk of clinically relevant pneumothorax after PTLB (hereafter called the CAPAD score), to guide patient management.

To externally validate the CAPAD score in an independent cohort, with a specific focus on its ability to rule out pneumothorax requiring drainage after PTLB.

We retrospectively analysed a pre-existing institutional database of consecutive adult patients undergoing CT-guided PTLB at Bichat–Claude-Bernard University Hospital (Paris, France) between 1 January 2015 and 31 December 2017. The CAPAD score combines five variables: COPD, Anterior PTLB approach, more than one Pleural crossing, pneumothorax ≥10 mm on the end-of-procedure CT (post-procedural immediate pneumothorax), and skin–pleura Distance ≤30 mm, with a pre-specified cut-off of 73 points. The primary endpoint was the diagnostic performance of the score for post-PTLB pneumothorax on the 4–6 h control CXR and secondary endpoint was its performance for pneumothorax requiring drainage.

The CAPAD score was computable in 313 of 474 patients. Pneumothorax occurred in 95 patients (30.4%), and 23 patients (7.3%) required drainage. At the pre-specified cut-off of 73, the score had a C-index of 0.77, a sensitivity of 75%, a specificity of 56%, a negative predictive value (NPV) of 84% and a positive predictive value of 43% for any post-PTLB pneumothorax. For pneumothorax requiring drainage, a score < 73 was associated with a 2.0% risk (3/147), corresponding to a NPV of 98%.

Our pragmatic CAPAD score demonstrated a good prognostic performance for predicting the risk of post-procedural pneumothorax, achieve a NPV of 98% for pneumothorax requiring drainage.