In renal disease, Albumin is first to appear In urine because-

In renal disease,comosition of Glomerular basement membrane is altered notably with loss of heparan sulfate moieties that form negatively charged filtration barrier(prevents loss of negatively charged serum protiens due to repulsion) This results in increased filtration of serum protiens into the urine predominantly negatively charged albumin. Ref:Harrison 20th edition pg no. 2144