Accuracy and Clinical Utility of Spot-Check Noninvasive Hemoglobin Monitoring: A Preliminary Study

Hemoglobin (Hb) monitoring is essential for perioperative management, particularly for detecting anemia and guiding transfusion decisions. Conventional invasive methods provide accurate results but are limited by delays, intermittent sampling, and iatrogenic blood loss. Noninvasive spot-check Hb (SpHb) monitoring offers rapid assessment, but its accuracy is unclear. This study thus evaluated agreement between SpHb obtained with the Rad-67 and invasive Hb measurements in anesthetized patients.

This single-center, prospective, observational study enrolled 25 adults who underwent gastrointestinal surgery under general anesthesia between June 2023 and March 2024. After induction and stabilization, SpHb was recorded simultaneously with arterial blood sampling. Reference Hb was measured with an automated hematology analyzer (XN-9100), an arterial blood gas analyzer (LC-661), and a portable spectrophotometric device (HemoCue). Correlation was assessed by Pearson's coefficient, and agreement by Bland-Altman analysis.

The cohort comprised 18 men (72.0%) with a mean (±SD) age of 66.8 ± 13.4 years and body mass index of 22.9 ± 3.2 kg/m². Mean Hb was 12.6 ± 1.7 g/dL (SpHb), 11.1 ± 1.8 g/dL (XN-9100), 11.4 ± 1.8 g/dL (LC-661), and 11.4 ± 1.8 g/dL (HemoCue). Strong correlations were observed (r = 0.931, 0.930, 0.841; p < 0.001 for all). Bland-Altman analysis showed fixed positive biases of +1.47 g/dL (XN-9100) and +1.19 g/dL (LC-661, HemoCue), without proportional error.

SpHb correlated strongly with invasive Hb but consistently overestimated values by 1-1.5 g/dL. While unsuitable as a direct substitute, SpHb may serve as a bias-aware screening tool that reduces unnecessary phlebotomy.