Central Vein stEnosis screeNing using Ultrasound guided Sniff test: A prospective diagnostic accuracy study (C-VENUS)

Central venous stenosis (CVS) is a clinically significant complication in patients who depend on long-term hemodialysis access. While digital subtraction angiography remains the diagnostic gold standard, it is invasive, costly, and exposes patients to contrast and radiation. This study examined the diagnostic value of a simple, non-invasive, radiation-free alternative-the ultrasound-guided "sniff test," which assesses dynamic changes in subclavian vein diameter during a forceful sniff to screen for CVS. Despite its potential advantages, the diagnostic performance of this method has not been well established.

A prospective study was conducted among 71 end-stage kidney disease (ESKD) patients scheduled for angiography. Each participant underwent a sniff test before the procedure. A reduction of more than 40% in subclavian vein diameter during sniffing was considered normal, indicating absence of stenosis. Angiographic findings were used as the reference standard. Clinical signs-specifically ipsilateral arm swelling and visible chest wall veins-were also evaluated for diagnostic utility.

Angiography confirmed CVS in 32 patients (45.1%). The sniff test showed a strong association with stenosis (OR 20.9) and demonstrated solid diagnostic performance, with sensitivity of 84.4%, specificity of 79.5%, and an AUC of 0.82. A normal sniff test accurately excluded stenosis in the majority of patients without CVS (86.1%), whereas an abnormal result was predominantly seen among those with stenosis (77.1%). Arm swelling was also significantly associated with stenosis (OR 20.40) and showed good standalone diagnostic accuracy (sensitivity 75.0%, specificity 87.2%, AUC 0.81). Importantly, combining the sniff test with clinical assessment enhanced overall performance, achieving higher specificity (94.9%) and excellent discriminative ability (AUC 0.90).

In conclusion, the ultrasound sniff test is a promising, accessible, and accurate screening tool for CVS. Used alone or alongside clinical findings, it offers a practical method to identify patients who may benefit from confirmatory angiography-particularly valuable in resource-limited or radiation-averse settings.