A homemade fiber-optic spectrometer has been fabricated for portable and on-site determination of microalbuminuria. The principle of the method was based on particle-enhanced turbidimetric-inhibition immunoassay (PETINIA), which was not affected by the hook effect phenomenon. This method was linear from 0 to 150 mg L-1 (r2 = 0.987), with a detection limit of 3.01 mg L-1 (S/N = 3). The intra-assay coefficient of variations (CVs) ranged from 3.1 - 4.8%, and the inter-assay CV was 6.7%, as assessed by calibration curves performed on three consecutive days. The precision of 10 replicate measurements of 50 mg L-1 HSA in a single analytical run was 6.5%. Interfering compound tests were satisfactory with recoveries of 95.0% to 105.8%. The system demonstrated its applicability to perform accurate measurements outside the laboratory for in-field analysis of the microalbuminuria (MAU) assay. The albumin concentrations in real urine samples measured by this system correlated well with the particle-enhanced turbidimetric immunoassay performed on a conventional spectrophotometer with r2 = 0.996 (n = 58).