A method and apparatus of non-invasively determining a blood circulatory hemoglobin value for a subject using a near-infrared spectrophotometric (NIRS) sensing device is provided. The method includes: a) non-invasively sensing tissue of the subject using the NIRS sensing device at about a time T1, and determining at least one NIRS tissue totalHb value； b) acquiring at least one circulatory blood sample from the subject at about the time T1； c) determining at least one blood circulatory THb value； d) calibrating the NIRS sensing device using the at least one blood circulatory THb value and the at least one NIRS tissue TotalHb value； and e) determining at least one blood circulatory hemoglobin value using the calibrated NIRS sensing device and the at least one NIRS tissue totalHb value.
