When using the camera method for a GFR, kidney counts should be compared to which of the following?

In the context of using the camera method for measuring glomerular filtration rate (GFR) in nuclear medicine, it is crucial to compare kidney counts to the pre-injection syringe counts. This comparison helps establish a baseline for the radioactivity that was administered during the procedure.

Pre-injection syringe counts represent the known quantity of the radiotracer that is injected into the patient. By comparing the kidney counts (which reflect the distribution and uptake of the radiotracer by the kidneys) to the pre-injection counts, clinicians can calculate the percentage of the injected dose that is filtered by the kidneys. This is essential for accurately determining the GFR, as it quantifies kidney function based on the amount of radiotracer excreted into the urine compared to what was administered.

This method provides a reliable measure of kidney function because it accounts for the total activity injected and allows for direct correlation to the radiotracer's activity that is found in the kidneys. Thus, the pre-injection syringe counts serve as a reference point for interpreting the subsequent kidney counts, making them a critical aspect of the GFR assessment.