How did a non-invasive hemoglobin test compare with laboratory testing before surgery?

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Measuring blood hemoglobin before surgery is important for diagnosing anemia. This prospective diagnostic test accuracy study aimed to monitor non-invasive spectrophotometric hemoglobin (SpHb, g/dL) in adults before elective surgery and examine its correlation and agreement with laboratory hemoglobin (Hb). A secondary aim was to identify SpHb cut-offs for anemia based on World Health Organization (WHO) definitions.

The study included 151 consecutive patients aged 18 years or older who presented for preoperative evaluation before scheduled elective general or orthopedic surgery.

Mean SpHb was 11.43 ± 2.01 g/dL (mean ± SD), underestimating mean laboratory Hb of 12.64 ± 2.29 g/dL (p < 0.001). The mean difference, or bias, between SpHb and Hb was −1.21 g/dL, with an SD of 1.76. This bias was inversely correlated with mean Hb concentrations. SpHb and Hb were positively correlated, with good reliability and a significant intraclass correlation (ICC).

SpHb diagnosed anemia in 32.3% of males and 60.3% of females. The SpHb cut-offs for identifying anemia were 11.3 g/dL for males and 10.2 g/dL for females; sensitivity was 83.3% and 62.9%, respectively. Specificity was 81% for males and 91.3% for females. The authors concluded that SpHb sensitivity allowed anemia diagnosis in males but not females. They also concluded that its specificity allowed anemia to be ruled out in both.