The usefulness of non-invasive co-oximetry haemoglobin measurement for screening pre-operative anaemia.

Pre-operative anaemia (haemoglobin < 13.0 g.dl-1 ) is a modifiable peri-operative risk-factor. This is screened for using formal laboratory testing. A non-invasive finger-probe sensor that can accurately measure haemoglobin is a possible alternative. This study considers the accuracy of non-invasive haemoglobin measurement using the Rad-67™ Rainbow (Masimo Corp., Irvine, CA, USA) compared with formal laboratory testing and its usefulness in detecting pre-operative anaemia. A total of 392 patients had measurements taken for non-invasive haemoglobin and perfusion index values using the Rad-67 Rainbow, alongside further peri-operative parameters and a formal laboratory haemoglobin test. Bland-Altman and sensitivity analysis showed that the limits of agreement between non-invasive and formal laboratory haemoglobin testing were between -1.95 g.dl-1 and 2.23 g.dl-1 (p < 0.001). The overall performance of non-invasive haemoglobin measurement was better in men than women (ROC 91.1% vs. 78.2%) and less biased in men, mean -0.08 (SD 1.09, 95%Cl -0.23-0.07) compared with women (mean 0.38 (SD 0.99, 95%CI 0.24-0.52)). Pre-operative anaemia was more prevalent in women than men (50.3% vs. 14.4%). The sensitivity of non-invasive anaemia detection (haemoglobin < 13 g.dl-1 ) was 66% for women and 52% for men. A non-invasive haemoglobin value of 14.0 g.dl-1 had an overall 91% sensitivity for detecting pre-operative anaemia (82% in men and 93% in women). The Rad-67 Rainbow is inadequate for the estimation of formal laboratory haemoglobin and lacks sensitivity for detecting pre-operative anaemia, especially in women. Further advancement in technology and accuracy is needed before it can be recommended as a routine pre-operative screening test.