Kidney Disorder

My mother, aged 77 having high blood pressure for the past 10 years.

Doctor said my mother has miscroscopic haematuria with overt proteinuria. The 24 hour urine quantification showed 4.9 gram of protein per day. The complements were normal. The Serum sodium was 132 mmol/L on 23/10/2009 and dropped further to 118 mmol/L 29/10/2009.

Is renal biopsy the only way to elucidate to the cause of the nephrotic range proteinuria? For 77 years old lady weight 38 kg with high blood pressure, is that advisable to do renal biopsy?

My mother and I are worry of the risk factor and hesitated to do, can you provide us your professional opinion? Thank you.