What is the treatment plan for a patient with impaired renal function, showing 5% differential renal uptake on the left and 95% on the right, with no significant tracer activity in the left renal pelvis on a nuclear medicine renal scan with Lasix (Furosemide), suggesting possible obstruction?

Treatment Plan for Severely Impaired Left Kidney (5% Function)

This patient requires urgent urology consultation for consideration of left nephrectomy, as the left kidney is essentially non-functional with only 5% differential uptake and no demonstrable excretion into the collecting system. 1

Immediate Management Steps

Surgical Evaluation

• Nephrectomy should be strongly considered given that differential renal function is far below the 40% threshold that typically prompts surgical intervention 1
• The complete absence of tracer activity entering the left renal pelvis indicates either complete obstruction or a non-functioning kidney that cannot be salvaged 1
• With only 5% function, this kidney contributes negligibly to overall renal function and poses risks including hypertension, infection, and potential malignant transformation 2

Pre-Surgical Workup Required

• Obtain renal ultrasound to assess for hydronephrosis, parenchymal thickness, and anatomical abnormalities that might explain the severe functional impairment 1
• Perform VCUG (voiding cystourethrogram) to exclude vesicoureteral reflux as a contributing factor, particularly if there is any history of urinary tract infections 1
• Verify contralateral kidney function is adequate (the right kidney at 95% function should be sufficient, but confirm normal anatomy and absence of obstruction) 1

Conservative Management (If Surgery Declined or Contraindicated)

Monitoring Protocol

• Serial MAG3 renal scans every 3-6 months to document any further functional decline (>5% change indicates progressive deterioration requiring intervention) 1
• Monitor blood pressure closely, as a non-functioning kidney can cause renovascular hypertension through renin-mediated mechanisms 2
• Screen for proteinuria, which may develop from hyperfiltration injury to the contralateral kidney 3

Prophylactic Measures

• Consider prophylactic antibiotics if there is any associated hydronephrosis or history of urinary tract infections, as stagnant systems are prone to infection 1
• Maintain adequate hydration to support the functioning right kidney 4

Key Clinical Decision Points

When Nephrectomy is Indicated

• Differential renal function <40% (this patient has only 5%) 1
• Recurrent infections in the affected kidney 1
• Uncontrolled hypertension attributable to the non-functioning kidney 2
• Progressive deterioration (>5% decline on serial scans) 1
• Symptomatic obstruction with pain or complications 1

When Conservative Management Might Be Considered

• Patient is a poor surgical candidate due to comorbidities 1
• Asymptomatic with stable imaging findings over time 1
• Bilateral renal disease where preservation of any function is critical 1

Critical Pitfalls to Avoid

Do not assume this is simply "obstruction" that can be relieved surgically to restore function - with only 5% uptake and no excretion, the kidney is likely irreversibly damaged from chronic obstruction, dysplasia, or chronic pyelonephritis 1

Do not delay evaluation - a non-functioning kidney can cause hypertension, recurrent infections, and rarely malignant transformation 2

Do not forget to assess the contralateral kidney thoroughly - the patient's entire renal function now depends on the right kidney, which must be protected from hyperfiltration injury and any unrecognized pathology 3

Follow-Up Imaging Strategy

• If nephrectomy is performed, no further renal scans of the left side are needed 1
• If conservative management is chosen, repeat MAG3 scan in 3-6 months to document stability or progression 1
• Annual ultrasound of the right kidney to monitor for compensatory hypertrophy and exclude new pathology 1, 3