title: Age dependence of renal function: clearance of iohexol and p-amino hippurate in healthy males.
abstract: Iohexol, a newly developed non-ionic contrast agent, has been recently documented as a reliable glomerular filtration marker. This study describes the age dependence of the single injection clearance of iohexol in a sample of healthy male volunteers ranging from 21 to 77 years of age. In parallel, renal plasma flow was studied by measuring the total clearance of p-amino hippuric acid administered as a continuous infusion. In subjects older than 50 years a negative correlation to age was found for both p-amino hippuric acid and iohexol clearance, with a reduction of 52 ml/min and 12 ml/min per decade, respectively, whereas no age dependence was found for younger subjects. Correlation between p-amino hippuric acid and iohexol clearances was 0.81. However, the filtration fraction, defined as the ratio of iohexol to p-amino hippuric acid clearance, was higher in the elderly subjects. A consistent discrepancy was found between total and renal clearances of p-amino hippuric acid, indicating significant renal metabolism. Renal clearance of creatinine was poorly correlated to iohexol clearance and did not show any relationship to age.
authors.affiliation: Department of Clinical Chemistry, Lund University, Sweden.
authors.forename: S E
authors.initials: SE
authors.lastname: Bäck
authors.forename: B
authors.initials: B
authors.lastname: Ljungberg
authors.forename: I
authors.initials: I
authors.lastname: Nilsson-Ehle
authors.forename: O
authors.initials: O
authors.lastname: Borgå
authors.forename: P
authors.initials: P
authors.lastname: Nilsson-Ehle
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000618:Aminohippuric Acids / Q000493:pharmacokinetics*; D005919:Glomerular Filtration Rate / Q000502:physiology; D006801:Humans; D007472:Iohexol / Q000493:pharmacokinetics*; D007668:Kidney / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012079:Renal Circulation / Q000502:physiology; D010130:p-Aminohippuric Acid / Q000493:pharmacokinetics*
chemical_list: D000618:Aminohippuric Acids; D007472:Iohexol; D010130:p-Aminohippuric Acid