Measurement of Renal Functional Reserve

The investigators will measure glomerular filtration rate using urinary clearance of cold
iothalamate before and after an oral protein load in patients with chronic kidney disease and
healthy volunteers.

Inclusion Criteria:

1. Age ≥18

2. Estimated GFR >30 mL/min/1.73m2

Exclusion Criteria:

1. Allergy to iothalamate, shellfish or iodine

2. Use of metformin or amiodarone

3. Inability to maintain a stable regimen of medications which affect GFR for > one week
prior to participation (e.g. non-steroidal anti-inflammatory drugs, angiotensin
converting enzyme inhibitors, angiotensin receptor blockers)

4. Use of medications which directly affect elimination of creatinine (e.g. cimetidine
and trimethoprim)

5. Acute exacerbation of asthma or chronic obstructive pulmonary disease within 3 months
requiring hospitalization or oral steroid therapy

6. Inadequate intravenous access

7. Severe anemia (Hct <21%)

8. Acute kidney injury (rise in creatinine to ≥1.5 times the previous baseline or by ≥
0.3 mg/dL on most recent labs prior to enrollment)

9. History of contrast-induced nephropathy

10. Hyperthyroidism

11. Pheochromocytoma

12. Sickle cell disease

13. Urinary retention or incontinence

14. Status post organ transplant

15. Pregnancy or active breast feeding

16. Cognitive impairment with inability to give consent

17. Institutionalized status