• Salvador Machlab, Pilar García-Iglesias, Eva Martínez-Bauer, Rafael Campo, Xavier Calvet, and Enric Brullet.
• Servicio de Aparato Digestivo, Hospital Universitari ParcTaulí. Institut d'Investigació i Innovació ParcTaulí, Barcelona, España. Departamento de Medicina. Universitat Autònoma de Barcelona, España.

ObjectivesThe American College of Gastroenterology's 2016 clinical guidelines for treating lower gastrointestinal (GI) tract bleeding recommends evaluating of nasogastric tube aspiration and the ratio of blood urea nitrogen (BUN) to creatinine to differentiate upper from lower GI bleeds. However, the evidence base to support recommending these 2 diagnostic variables is low. This study aimed to evaluate the diagnostic utility of nasogastric tube aspiration and the BUN-to-creatinine ratio for distinguishing between upper and lower GI bleeding.Material And MethodsWe conducted a systematic review of the literature to find studies reporting the diagnostic precision of the BUN-to-creatinine ratio and nasogastric aspiration in patients with GI bleeding without hematemesis.ResultsThe sensitivity of both methods is low for detecting upper GI bleeding. Both blood in the aspirate and an elevated BUN-to-creatinine ratio significantly increase the probability of finding an upper GI source. The positive likelihood ratio varies from positive 2 to 11. However, the sensitivity of both tests for a diagnosis of upper GI bleeding is very low (negative likelihood ratio of 0.6).ConclusionA negative result on either of the 2 diagnostic tests provides little useful information and does not firmly rule out an upper GI bleed. Nasogastric tube aspiration cannot be recommended for distinguishing between upper and lower GI bleeding. If the diagnosis is in doubt, endoscopic exploration of the upper GI tract is necessary.

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