Determination of hemoglobin levels in the finger using near infrared spectroscopy

We previously demonstrated that near-infrared spectroscopy can be used to measure blood flow. The spectrum of blood is dominated by hemoglobin. Therefore, it should be possible to determine the concentration of hemoglobin in tissue using near-infrared transmittance. We attempted to do this in the finger using a unique handheld multiple wavelength spectrophotometer. We took samples from 73 subjects and performed repeat measurements in several subjects. Hemoglobin level was determined at the time of near-infrared measurement. We performed correlation analysis between the hemoglobin values and the absorbance values. There was a strong correlation between hemoglobin levels and the 14 wavelengths (r = 0.738, n = 121, SEE = 1.7). We categorized the patients by hemoglobin level as either normal (12-16 g/dl), mildly anemic (10-12 g/dl), or moderately anemic (<10 g/dl). There were 21 patients in the low hemoglobin group, 29 in the middle range, and 23 in the normal range. The mean hemoglobin levels were 8.4 +/- 0.3 g/dl for the low group, 10.9 +/- 0.1 g/dl for the mildly anemic group, and 13.8 +/- 0.3 g/dl for the group with normal hemoglobin. There was a clear separation of absorbance values among the three groups. The major differences seen were in the midrange of the spectrum. It is encouraging that this first study of hemoglobin measurement yielded data permitting a discrimination of hemoglobin levels. It is hoped that future refinements will lead eventually to a non-invasive technique for the measurement of blood hemoglobin concentration.