Adolescent nephro-urology

Biochemical control. Renal function is assessed from plasma creatinine and, ideally, a yearly isotopic measurement of glomerular filtration rate (GFR). Until the patient has stopped growing, GFR can be estimated using the Schwartz formula (height in cm x 40/creatinine mmol/l). GFR increases rapidly in the first two years of life to adult values, provided that it is adjusted for body surface area. Plasma creatinine is proportional to muscle mass; most serious misappreciations of renal insuffic iency occur because the creatinine value, although raised for that individual, is still within the ‘normal’ adult range. Serum bicarbonate must be kept above 20 mmol/ l, as acidosis is associated both with increased protein catabolism and growth failure, and with bone disease due to bone buffering of H+ ion. Supplementation is with oral sodium bicarbonate. Correcting acidosis will help control hyperkalaemia. Unlike adults, adolescents with chronic renal failure (CRF) are often salt losers as tubular abnormalities are common, so sodium chloride supplementation may be required to avoid hypotension and hypovolaemia (serum sodium will be normal). Patients with obstructive uropathy are often unable to concentrate their urine; this results in polyuria, so access to fluids is necessary at all times.