tokens: Tubular dysfunction in renal lithiasis : cause or consequence ? ] To investigate whether overall tubular dysfunction is encountered in a particular subgroup of patients with urolithiasis , the following parameters of renal tubular function have been measured in fasting morning urine in 124 male stone formers : excretion of lysozyme and gamma - glutamyl transpeptidase ( gamma - GT ) , fractional excretion ( FE ) or glucose , insulin , bicarbonate after an alkali load , and theoretical phosphate threshold ( TmP / GFR ) .