The half-life of elimination which is also known as the biological half-life is defined as the time required for the serum drug concentration to reach 50%. The glomerular filtration rate (GFR) is a common test that evaluates kidney function in filtering the blood, most often used to assess acute and chronic kidney disease (CKD) (Jensen & Peppers, 2005). Both terms essentially deal with the pace at which the human body processes and filters an external solution/drug administered into the body.
In the context of an IV contrast-enhanced exam, diagnostic imaging requires the use of iodinated contrast media in patients. It is immediately diluted in circulated blood, and there is no significant protein binding, deposition in tissues, metabolism, or deiodination. In a person with normal renal function, the half-life of the agents is 30-60 minutes, but with renal function impairment, it can be delayed between 20 to 140 hours (Widmark, 2007).
However, iodinated contrast media is considered neurotoxic and may cause what is known as contrast-induced nephropathy (CIN), especially in patients with CKD. GFR through serum creatinine concentration or a more accurate eGFR is used to determine renal function. The GFR rate is critical for knowing whether it is safe and appropriate to use iodinated contrast media since a patient with impaired renal function faces a high potential risk of CIN. There is no agreed-upon risk threshold, but clinical and individual characteristics of the patient should be considered, and radiology practices have used various measures between 1.5 mg/dL and 2.0 mg/dL GFR as the cut-off, with thresholds lower for diabetes mellitus patients. Furthermore, the half-life is a considerable factor as well, for both normal and impaired renal function patients since another risk factor for CIN is repeated dosage. Therefore, for a normal person, it may take up to 20 hours for complete removal of iodinated contrast, and it is recommended to administer it only once per 24 hours barring an emergency, for safety reasons (ACR, 2020).
References
ACR. (2020). ACR manual on contrast media. Web.
Jensen, S., & Peppers, M. (2005). Pharmacology and drug administration for imaging technologists (2nd ed.). Mosby
Widmark, J. M. (2007). Imaging-related medications: A class overview. Baylor University Medical Center Proceedings, 20(4), 408–417. Web.