In-vivo devices, systems and methods for the detection of blood within in-vivo bodily fluids. The methods include irradiating in-vivo fluids passing through a gap in a housing of an in-vivo device introduced to the GI tract of a subject with a plurality of illumination sources positioned on a first side of a gap; detecting with at least one light detector positioned on the opposite side of the gap and facing the illumination sources, light irradiated by the illumination sources; transmitting a plurality of values representing the light detected over time; converting these values to blood concentration values over time, and comparing the blood concentration values to a predetermined threshold value. Based on the comparison, the method includes determining the type of bleeding profile, such that if a plurality of blood concentration values measured consecutively is above the threshold value, the bleeding profile indicates bleeding.