From the Guidelines
A non-functioning kidney on a renal scan is typically defined as a kidney that contributes less than 10% of total renal function. This definition is based on the guidelines outlined in the 2005 practice guidelines for the management of patients with peripheral arterial disease, as reported in the journal Circulation 1. According to these guidelines, a kidney that contributes less than 10% of total renal function may be considered for nephrectomy, especially if there is evidence of irreparable ischemic atrophy or injury.
Key Considerations
- The kidney length is also an important factor, with a length of less than 5 cm suggesting poor function 1.
- Extensive damage to the kidney may also indicate poor function and potentially warrant nephrectomy.
- Before proceeding with nephrectomy, a comprehensive evaluation should be performed, including assessment of overall renal function with estimated glomerular filtration rate (eGFR), serum creatinine, and possibly a 24-hour creatinine clearance test.
- The contralateral kidney should have at least 20-25% function (ideally >40%) to maintain adequate renal function after nephrectomy.
Management
- Management of a non-functioning kidney depends on the underlying cause, patient symptoms, and comorbidities.
- In some cases, especially with recurrent infections, pain, or hypertension attributed to the non-functioning kidney, nephrectomy provides definitive treatment.
- However, in asymptomatic patients with stable function in the remaining kidney, conservative management with regular monitoring may be appropriate.
- The decision should be individualized based on the patient's overall health status, surgical risk, and quality of life considerations, as emphasized in the guidelines 1.
From the Research
Renal Function Cutoff for a Non-Functioning Kidney
- The renal function cutoff for a non-functioning kidney on a renal scan is generally considered to be a split renal function (SRF) of less than 10% 2, 3.
- This cutoff is used to define a non-functional kidney, which is often characterized by paper-thin parenchyma and significantly impaired renal function 2.
- Studies have shown that kidneys with an SRF of less than 10% may still have the potential for functional recovery with appropriate treatment, such as percutaneous nephrostomy (PCN) 3.
- The use of imaging studies, such as nuclear renal scans and computerized tomography (CT) scans, can help to assess renal function and guide treatment decisions 4, 5.
Diagnostic Criteria
- A non-functional kidney is typically defined as one with an SRF of less than 10% on a nuclear scan 2, 3.
- CT scans can also be used to estimate renal function by measuring renal parenchymal volume, which has been shown to correlate strongly with differential renal function 4.
- The diagnosis of a non-functioning kidney should be made based on a combination of clinical evaluation, imaging studies, and laboratory tests.
Treatment Implications
- The treatment of a non-functioning kidney depends on the underlying cause of the impairment and the patient's overall clinical condition 2, 3.
- In some cases, treatment with PCN or other interventions may be able to improve renal function and avoid the need for nephrectomy 3.
- However, in other cases, nephrectomy may be necessary to relieve symptoms and prevent further complications 2, 3.