Observer accuracy and reproducibility of visual estimation of blood loss in obstetrics: how accurate and consistent are health-care professionals?

Objectives To evaluate the observer accuracy and intra-observer test–retest reliability of visual estimation of blood loss by midwives and obstetricians. Methods This was a prospective, single-blinded observational study conducted at a London teaching hospital. The accuracy of visually estimating five maternity pads that had been soaked with 25, 50, 100, 150 and 200 ml of blood was assessed. The reproducibility in estimating the same volume (two sets of pads soaked with 50, 100, 150 and 200 ml of blood randomly placed at separate stations) was evaluated by asking participants to visually estimate these volumes. Results Although there is a tendency to overestimate, the mean percentage difference (estimated–actual volumes) was not significantly different among consultants, trainees and midwives. Visual estimations were especially inaccurate with smaller volumes, which could be overestimated by up to 540%. Test–retest reliability was poor for the larger volumes but statistically acceptable for the smaller volumes, although the difference between the two estimates of the same volume could be as much as 300%. Conclusions Visual estimations were inaccurate by health-care professionals who have a tendency to overestimate. Experience did not appear to have a confounding effect on accuracy. Further training in visual assessment skills is necessary in order to improve the clinicians’ estimation.