Methods of measurement of biometric indicators in a mammalian subject are described. Biometric indicators of interest include hematocrit, plasma volume, volume of distribution, and glomerular filtration rate. The methods are especially applicable to subjects with rapid blood loss and to subjects with unstable hematocrits. Hematocrit may be measured by administering an injectate with a dynamic fluorescent marker and a static fluorescent marker, or a single static marker with two fluorescent tags, into the vascular system of the subject, and monitoring the emission intensities of the markers or fluorescent tags over a period of time. Hematocrit may then be calculated using a calibrated spectrometric analyzer by determining the raw ratio of the markers at To, calculating the apparent hematocrit, and applying a correction factor.
