# Chronic Kidney Disease for the Urologist

## Introduction

Chronic kidney disease (CKD) is a common condition, affecting about 15% of adults in the United States. Urologists frequently encounter patients with CKD in various contexts, ranging from obstructive uropathy and nephrolithiasis to renal surgery and postoperative follow-up. A thorough understanding of CKD staging, the urologic causes and consequences of CKD, the effects of CKD on perioperative management, and the principles of renal preservation is crucial for delivering safe and effective urologic care.

## Definition and Staging

### KDIGO Definition

CKD is defined by the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines as abnormalities in kidney structure or function that persist for more than three months and have implications for health. This diagnosis requires either a glomerular filtration rate (GFR) below 60 mL/min/1.73 m² for over three months or the presence of markers of kidney damage. These markers include albuminuria, abnormalities in urine sediment, histologic changes, structural abnormalities detected by imaging, or a history of kidney transplantation.

### GFR Staging

CKD is staged based on GFR levels. Stage G1 corresponds to a GFR of 90 mL/min/1.73 m² or higher, indicating normal or high kidney function but with evidence of kidney damage. Stage G2 includes a mildly decreased GFR between 60 and 89. Stage G3 is subdivided into G3a (GFR 45-59) and G3b (GFR 30-44), reflecting mild to moderate and moderate to severe decreases in kidney function, respectively. Stage G4 represents a severely decreased GFR between 15 and 29, and stage G5 indicates kidney failure with a GFR below 15.

### Albuminuria Staging

Albuminuria is categorized into three stages based on the albumin-to-creatinine ratio. Stage A1 is less than 30 mg/g, considered normal to mildly increased. Stage A2 ranges from 30 to 300 mg/g, representing moderately increased albuminuria or microalbuminuria. Stage A3 is greater than 300 mg/g, indicating severely increased albuminuria or macroalbuminuria.

| GFR Stage | GFR (mL/min/1.73 m²) | Description |
|---|---|---|
| G1 | ≥90 | Normal or high (with evidence of kidney damage) |
| G2 | 60-89 | Mildly decreased |
| G3a | 45-59 | Mild to moderately decreased |
| G3b | 30-44 | Moderately to severely decreased |
| G4 | 15-29 | Severely decreased |
| G5 | <15 | Kidney failure |

| Albuminuria Stage | ACR (mg/g) | Description |
|---|---|---|
| A1 | <30 | Normal to mildly increased |
| A2 | 30-300 | Moderately increased (microalbuminuria) |
| A3 | >300 | Severely increased (macroalbuminuria) |

### GFR Estimation

The CKD-EPI equation, updated in 2021, is the recommended formula for estimating GFR using serum creatinine, age, and sex, with the race variable removed in the latest revision. Cystatin C serves as an alternative marker less influenced by muscle mass and is particularly useful when creatinine-based estimates are unreliable, such as in patients with extreme body habitus or amputations. For clinical decisions requiring precise GFR measurement, nuclear medicine techniques using Tc-99m DTPA or Cr-51 EDTA remain the gold standard.

<image>KDIGO heat map showing CKD prognosis based on GFR category (G1-G5 on vertical axis) and albuminuria category (A1-A3 on horizontal axis), with color coding from green (low risk) through yellow and orange (moderate risk) to red (very high risk), indicating frequency of monitoring and referral recommendations</image>

## Urologic Causes of CKD

### Obstructive Uropathy

Obstructive uropathy is the most important reversible cause of CKD encountered by urologists. Bilateral ureteral obstruction or obstruction of a solitary kidney can lead to acute kidney injury that progresses to CKD if left untreated. Common causes include benign prostatic hyperplasia (BPH), bilateral ureteral stones, retroperitoneal fibrosis, pelvic malignancies, and posterior urethral valves in pediatric patients. Following relief of bilateral obstruction, patients may experience post-obstructive diuresis, characterized by massive polyuria that necessitates careful fluid and electrolyte management. The recovery of renal function depends on the duration and severity of the obstruction, with partial recovery possible even after prolonged obstruction.

### Nephrolithiasis

Recurrent kidney stones and the interventions required to manage them can contribute to CKD. Conditions such as cystinuria, primary hyperoxaluria, and struvite staghorn calculi carry the highest risk for CKD development. Percutaneous nephrolithotomy (PCNL) and repeated surgical procedures can cause parenchymal loss. Therefore, medical prevention of stone recurrence is critical for long-term renal preservation.

### Reflux Nephropathy

Chronic vesicoureteral reflux accompanied by recurrent pyelonephritis leads to cortical scarring, which is a leading cause of CKD and end-stage renal disease in children and young adults. The dimercaptosuccinic acid (DMSA) scan is the gold standard imaging modality for detecting cortical scars.

### Post-Surgical CKD

Radical nephrectomy results in new-onset CKD stage 3 or higher in approximately 20-25% of patients. Partial nephrectomy, a nephron-sparing approach, reduces the risk of CKD and is preferred for T1a renal masses. Warm ischemia time exceeding 25 minutes increases the risk of long-term renal function decline. Partial nephrectomy is imperative in cases involving a solitary kidney, bilateral tumors, or pre-existing CKD.

### Neurogenic Bladder

Chronic high-pressure storage and recurrent urinary tract infections in patients with neurogenic bladder cause progressive deterioration of the upper urinary tract. These patients require lifelong monitoring of renal function and upper tract imaging to prevent CKD progression.

## Impact of CKD on Urologic Practice

### Perioperative Considerations

CKD affects perioperative management in several ways. Anemia due to erythropoietin deficiency is common, and the target hemoglobin level before surgery is 10 to 11.5 g/dL. Uremic platelet dysfunction increases bleeding risk, and desmopressin (DDAVP) may be used to improve hemostasis. Electrolyte abnormalities such as hyperkalemia necessitate avoidance of succinylcholine and close ECG monitoring. Metabolic acidosis and hyperphosphatemia are also concerns. Volume management is challenging due to impaired concentrating ability; thus, dehydration and nephrotoxic agents should be avoided. Many medications require renal dose adjustments, including antibiotics like aminoglycosides, vancomycin, and fluoroquinolones. Analgesics such as NSAIDs should be avoided, and opioid doses reduced due to renally cleared metabolites. Contrast agents require pre-hydration with isotonic saline, and metformin should be held if the estimated GFR is below 30.

### Contrast-Induced Nephropathy

The risk of contrast-induced nephropathy increases significantly when eGFR falls below 30 mL/min. Prevention strategies include intravenous isotonic saline hydration at 1 mL/kg/hour for 6 to 12 hours before and after the procedure. Iso-osmolar or low-osmolar contrast agents should be used, and contrast volume minimized. For vascular procedures, CO2 angiography may be considered as an alternative. N-acetylcysteine is no longer recommended, as the PRESERVE trial demonstrated no benefit.

### Medication Considerations

Nephrotoxic agents such as NSAIDs, aminoglycosides when possible, and intravenous contrast should be avoided. ACE inhibitors and angiotensin receptor blockers (ARBs) are renoprotective in diabetic and proteinuric CKD but require monitoring for hyperkalemia and acute declines in GFR. Alpha-blockers and 5-alpha reductase inhibitors are safe in CKD and do not require dose adjustments. Anticholinergics are generally safe but warrant monitoring for constipation and urinary retention in CKD patients.

## Renal Preservation Strategies

### Surgical Principles

Partial nephrectomy should be performed whenever technically feasible for renal masses, especially in patients with a solitary kidney, bilateral tumors, or CKD. Warm ischemia time should be minimized to less than 20 to 25 minutes, with cold ischemia using ice slush reserved for complex cases. Selective arterial clamping helps preserve perfusion to non-tumor-bearing parenchyma. Zero-ischemia techniques, such as off-clamp partial nephrectomy for exophytic tumors, reduce nephron loss.

### Medical Strategies

Blood pressure control with a target below 130/80 mmHg is essential, with ACE inhibitors or ARBs as first-line agents for proteinuric CKD. Sodium-glucose cotransporter-2 (SGLT2) inhibitors, including dapagliflozin and empagliflozin, provide renoprotective benefits independent of diabetes status, as demonstrated in the DAPA-CKD and EMPA-KIDNEY trials. Preventing metabolic stone recurrence reduces the need for repeated interventions and preserves renal function. Avoiding nephrotoxins such as NSAIDs, ensuring adequate hydration, and using contrast agents judiciously are critical components of renal preservation.

<image>Diagram illustrating urologic strategies for renal preservation, comparing radical nephrectomy (showing complete kidney removal with compensatory hypertrophy of the contralateral kidney) versus partial nephrectomy (showing tumor excision with preservation of remaining parenchyma), with graphs showing expected GFR trajectories over time for each approach</image>

## When to Refer to Nephrology

Referral to nephrology is indicated when the estimated GFR falls below 30 mL/min (CKD stage 4-5) for dialysis planning and transplant evaluation. Rapidly declining GFR, defined as a decline greater than 5 mL/min per year, significant proteinuria in the A3 category (greater than 300 mg/g), refractory hypertension, or electrolyte abnormalities also warrant nephrology consultation. Pre-surgical optimization in patients with advanced CKD and post-surgical acute kidney injury that does not respond to conservative management are additional indications for referral.

## Key Clinical Pearls

Obstructive uropathy remains the most important reversible cause of CKD in urologic practice, so it is essential to assess the upper urinary tracts in patients with CKD of unclear etiology. Partial nephrectomy is the standard of care for T1a renal masses and is imperative in patients with CKD, a solitary kidney, or bilateral tumors. Normal serum creatinine levels do not exclude significant CKD; therefore, always calculate the estimated GFR. Radical nephrectomy results in new-onset CKD stage 3 or higher in approximately 20-25% of patients, which carries important cardiovascular and mortality implications. SGLT2 inhibitors have become a cornerstone of CKD management regardless of diabetes status, with strong evidence supporting their role in slowing disease progression. Post-obstructive diuresis can cause life-threatening dehydration and electrolyte disturbances, so careful monitoring of urine output and judicious replacement of losses are critical.

## References

1. Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 clinical practice guideline for the evaluation and management of chronic kidney disease. *Kidney Int*. 2024;105(4S):S117-S314.  
2. Weight CJ, Larson BT, Fergany AF, et al. Nephrectomy induced chronic renal insufficiency is associated with increased risk of cardiovascular death and death from any cause in patients with localized cT1b renal masses. *J Urol*. 2010;183(4):1317-1323.  
3. Heerspink HJL, Stefansson BV, Correa-Rotter R, et al. Dapagliflozin in patients with chronic kidney disease. *N Engl J Med*. 2020;383(15):1436-1446.  
4. Davenport MS, Perazella MA, Yee J, et al. Use of intravenous iodinated contrast media in patients with kidney disease. *Radiology*. 2020;294(3):660-668.