Abstract: A test kit and a biomedical process is provided to estimate metals particularly non-transferrin bound iron levels (NTBI) in circulating body fluids particularly, serum. NTBI appears in serum when there is excess iron in the body. The method comprises of employing a signal generating moiety capable of complexing with iron that is a peptide like molecule having an iron binding site and also an optical signal generating functional group. The molecule is of microbial origin. The measurement is based on the alteration of optical characteristics of the probe molecule upon attachment of iron to its binding site on the molecule. Hence it generates a signal proportionate to the amount of iron available for binding and provides a direct estimate of free or unbound iron in the sample. According to this instant invention a rapid estimation method of NTBI in body fluids can be undertaken in an inexpensive way without the need of specialized expertise.