2hours and 30 minutes into hemodialysis treatment, machine alarmed.Treatment stopped, blood leak confirmed with blood leak test strip.No visible blood on dialyzer.Blood was not returned, undetermined amount of blood loss, estimated minimal.No medical interventions or hospitalization.Priming conditions: bfr=150ml/min and priming volume=1000ml.Dialysis conditions: tx time=3hrs, bfr=350ml/min, dfr=sequential (uf only), access= avf with 16g needle 1".