An important iatrogenic cause of anaemia in the intensive care unit is loss of the discarded blood during phlebotomy via indwelling vascular catheters. A closed system blood conservation device has previously been shown to reduce the need for blood transfusion and to blunt the decrease of haemoglobin in intensive care unit patients. However such a device may not benefit patients who are admitted with a relatively preserved haemoglobin. In this sub-group analysis of a before-and-after study, 128 patients had admission haemoglobin > or =115 g/l and did not receive any blood transfusions while in the intensive care unit. In the control group of 50 patients a blood conservation device was not used, while in the active group of 78 patients the device was used. Use of the blood conservation device did not affect the haemoglobin trends when both groups were compared using the general linear model. For patients with admission haemoglobin > or = 115 g/l, use of a blood conservation device does not affect the subsequent rate of haemoglobin decline in the intensive care unit. These patients are unlikely to benefit from the use of such devices.