Iodine-123 labelled ortho-Iodohippuric Acid ([I-123]-OIH) was used in the early 1970's as a kidney imaging agent or tracer that "lights-up" inside your body when scanned, but over the years its use has declined. The most commonly used tracer is Technetium-99m labelled Mercaptoacetyltriglycine ([Tc-99m]-Mertiatide or [Tc-99m]-MAG3). However, long-term shortages may threaten the supply of the radioactive substance Tc-99m in Canada and the world. As a result of such shortages, there is a need to identify other types of tracers that can be used for imaging. [I-123]-OIH may be an alternative.

The purpose of this study is to examine the diagnostic performance characteristics of [I-123]-OIH in comparison to [Tc-99m]-MAG3.

This study is being conducted to compare two imaging agents (tracers): [I-123]-OIH and [Tc-99m]-MAG3 using gamma camera imaging in participants with different levels of kidney function. Gamma camera imaging is a non-invasive nuclear scan that is used to look at organs and tissues inside the body. An imaging agent or tracer is a radioactive chemical intravenously injected into your body which lights up cells, tissues and organs. The study will evaluate the safety of a single injection of [I-123]-OIH and compare the imaging results and the calculated renal function values (using blood tests) to those of [Tc-99m]-MAG3 . 90 participants are required to complete this study.

Inclusion Criteria:

• At least 18 years of age.
• Provide signed informed consent.
• Documented stable renal impairment with an eGFR < 60/mL/min/1.73m^2 by two eGFR measurements within 3 months that are within ± 15% of each other or healthy prospective kidney donor with an eGFR ≥ 60 mL/min/1.73m^2.

Exclusion Criteria:

• Females who are pregnant, planning to become pregnant or are lactating.
• Clinically relevant abnormal findings that could, in the opinion of the investigator, interfere with the safe completion of the study.
• Unable, in the opinion of the clinician or investigator, to tolerate fluid intake required for radionuclide renography.
• Participation in any clinical trial involving an investigational product within 30 days prior to the first injection.
• Not using an adequate method of family planning unless the participant, or the male participant's partner, has had a hysterectomy, a tubal ligation, is postmenopausal or is not at risk of pregnancy.
• Unable to lie still in a supine position for at least 30 minutes.
• Unable to complete study procedures, including follow-up safety assessments.
• Medical or psychological conditions that on assessment by the principal investigator make the participant unable to complete the procedure.
• History of allergic reaction to iodine or iodine compounds, inclusive of iodinated x-ray contrast media.
• Any other conditions that may impact the participant's ability to complete the study.

Participants will be recruited from both healthy subjects (eGFR ≥ 60 mL/minute/1.73m^2) being assessed as potential renal donors and patients having suspected renal impairment (eGFR <60 mL/minute/1.73m^2). Severity of disease will be determined based on estimated glomerular filtration rate (eGFR) derived from serum creatinine concentration.