Measurement of Hemoglobin Concentrations Using the Astrim<sup>TM</sup> Noninvasive Blood Vessel Monitoring Apparatus

Abstract

Several noninvasive measuring methods using near-infrared radiation (wavelength 700–2,500 nm), which has a better biologic penetration than infrared and visible radiation, have been reported [1, 2]. In 1999, Sysmex (Kobe, Japan) developed a device to measure hemoglobin (Hb) using near-infrared radiation (AstrimTM) [3]. We report our study of the correlation between Hb levels determined by Astrim and by the SE-9000TM automatic cell analyzer used in our central laboratory.Astrim(fig. 1) can visualize veins running close to the surface of the skin by locating near-infrared radiation on the dorsal side of the fingers. A CCD camera is placed on the opposite side as a light acceptor. We summarize the principle as follows: if ‘I₀’ is near-infrared radiation penetrating the skin, and ‘It’ is near-infrared radiation after permeation of the skin, then ‘log (I₀/It) = ECD’ according to the Lambert-Beer law [4], where E = absorption coefficient of Hb, C = total concentration of Hb and HbO2 and D = diameter of the vessel permeated. With the assumption that the near-infrared radiation entering the skin has the same wavelength as that absorbed by Hb and HbO2, the formula can be rewritten as ‘total Hb = log (I₀/It)/ED’. This formula is correct in ideal conditions, when there is no scattered or reflected light. In the case of near-infrared radiation, however, it is approximate, since scattered and reflected light in the blood and tissue cannot be disregarded. A program based on this formula is integrated in this device. We examined 91 patients visiting our section for treatment (28–79 years old, mean age: 54, male: 34, female: 57). Before the Astrim measurement was performed, the patients rested in a sitting position at room temperature (25°C) for about 10 min. On the day we performed this examination, we also took 2 ml of peripheral blood from each of the subjects, and measured Hb level with the SE-9000. The results are shown in table 1. No significant difference in Hb concentration was noted between the two groups (t test, risk ratio 0.05 or below), and results for the groups were significantly correlated (fig. 2). However, in the 12 patients with multiple myeloma, the correlation was not as strong (p = 0.488), possibly because the blood flow in the peripheral vessels was decreased due to hypergammaglobulinemia, resulting in scattered and reflected light. The results of this study suggest that Astrim could be a useful screening test for Hb concentrations. If inconsistencies between Hb concentrations measured by Astrim and those measured by an automatic cell analyzer are apparent, additional tests for differentiation from diseases which cause peripheral vascular disorder or decrease in peripheral blood flow may be required.