Comparison of iothalamate clearance methods for measuring GFR

Pharmacotherapy. 1999 Aug;19(8):943-50. doi: 10.1592/phco.19.11.943.31576.


Study objective: To evaluate the bias and precision of three methods of measuring glomerular filtration rate (GFR) relative to a standard method.

Design: Prospective, outpatient study.

Setting: University-affiliated general clinical research center.

Patients: Twenty-six patients with various degrees of renal function (GFR range 25-151 ml/min/1.73 m2).

Interventions: Each patient received iothalamate twice during the study visit, first as a bolus injection and then as a priming dose followed by a constant-rate infusion for 2.5 hours.

Measurements and main results: Plasma (ClpIVB) and renal clearances (ClrIVB) after bolus injection and plasma clearance during constant-rate infusion (ClpINF) were compared with standard renal clearance during constant-rate infusion (ClrINF). All three measures were highly correlated with ClrINF (r>0.90, p<0.001). The mean ClrIVB was not significantly different from ClrINF (106.3+/-30.4 vs 104.2+/-28.5 ml/min/1.73 m2) and provided a precise (8.8%, 95% CI 6.5-11.1%) and unbiased measure of GFR. Both ClpIVB and ClpINF were positively biased; values exceeded ClrINF by 11.8+/-11.1 (p=0.0001) and 10.5+/-12.5 ml/min/1.73 m2 (p=0.0003), respectively. Use of a nonrenal correction factor of 9.8 and 10.5 ml/min/1.73 m2 for infusion and bolus plasma clearance values, respectively, eliminated bias and improved the precision of these methods.

Conclusions: Iothalamate renal clearance after bolus injection is a simple, accurate, and precise measurement of GFR and may be a useful alternative to the standard infusion method in clinical investigations. The corrected plasma clearance provides a simple index of GFR for clinical practice.

Publication types

  • Clinical Trial
  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Aged
  • Contrast Media / pharmacokinetics*
  • Female
  • Glomerular Filtration Rate / physiology*
  • Humans
  • Iothalamic Acid* / pharmacokinetics
  • Male
  • Middle Aged
  • Outpatients
  • Prospective Studies


  • Contrast Media
  • Iothalamic Acid