Chronic Kidney Disease — Staging and Management

• Nephron loss and hemodynamic adaptation: The initial insult (glomerular injury, tubular injury, vascular disease, or interstitial fibrosis) results in irreversible loss of functioning nephrons. Surviving nephrons undergo compensatory hyperfiltration through increased glomerular capillary hydraulic pressure, mediated by afferent arteriolar vasodilation and efferent arteriolar vasoconstriction. This is mediated by increased renin-angiotensin-aldosterone system (RAAS) activation, enhanced prostaglandin and nitric oxide production, and altered eicosanoid metabolism. While initially adaptive, this hyperfiltration creates excessive mechanical stress (tensile strain) on the glomerular basement membrane and podocytes, accelerating their injury and death. Over time, this maladaptive response perpetuates a self-perpetuating cycle of nephron loss independent of the original disease process.

• Proteinuria and glomerular injury progression: Albuminuria (and broader proteinuria) reflects loss of glomerular charge and size selectivity due to podocyte dysfunction and basement membrane damage. Filtered proteins, particularly albumin and immunoglobulins, are reabsorbed by proximal tubule cells via receptor-mediated endocytosis and are toxic when present in pathologic quantities. These proteins activate intracellular signaling (NF-κB, Wnt/β-catenin pathways) leading to production of transforming growth factor-beta (TGF-β), monocyte chemoattractant protein-1 (MCP-1), and other pro-fibrotic cytokines. Proteinuria is both a marker of glomerular injury and an independent driver of progression, making its reduction therapeutically important. The degree of albuminuria correlates with progression risk and cardiovascular mortality, making it a key modifiable risk factor.

• Tubulointerstitial fibrosis and tubular dysfunction: Progressive tubulointerstitial fibrosis (TIF) is the final common pathway of CKD regardless of initial etiology. This occurs through epithelial-mesenchymal transition (EMT) of tubular epithelial cells, infiltration by immune cells (macrophages, T lymphocytes), and proliferation of fibroblasts and myofibroblasts. The fibrotic response is driven by TGF-β/Smad signaling, RAAS activation, sympathetic nervous system stimulation, and hypoxia. Tubular dysfunction leads to impaired reabsorption and secretion of solutes and water, contributing to electrolyte abnormalities, acid-base disorders, and progression. Hypoxia in the CKD kidney (due to increased metabolic demand and altered perfusion) perpetuates fibrosis and inflammation. As fibrosis progresses, peritubular capillary rarefaction occurs, further reducing oxygen delivery and accelerating the decline.

• Abnormal mineral and bone metabolism (CKD-MBD): Progressive GFR decline impairs phosphate excretion, leading to hyperphosphatemia and secondary hyperparathyroidism. Declining GFR also reduces 1,25-dihydroxyvitamin D (calcitriol) production due to loss of renal 1α-hydroxylase activity, causing hypocalcemia. Hyperphosphatemia and hypocalcemia stimulate parathyroid hormone (PTH) secretion, which increasingly loses effectiveness in restoring phosphate and calcium homeostasis as renal function declines. Chronic secondary hyperparathyroidism leads to renal bone disease, vascular calcification, and increased cardiovascular mortality. Additionally, high FGF23 (fibroblast growth factor 23) levels in CKD promote phosphaturia but also contribute to left ventricular hypertrophy and progression of kidney disease.

• Systemic inflammation and immune activation: CKD is characterized by chronic low-grade inflammation with elevated inflammatory markers (C-reactive protein, IL-6, TNF-α) independent of infection. This results from uremic retention of pro-inflammatory solutes, altered gut microbiota, endotoxemia from bacterial lipopolysaccharide translocation, and oxidative stress. Oxidative stress in CKD arises from impaired antioxidant defenses, mitochondrial dysfunction, and NADPH oxidase activation. Persistent immune activation and inflammation accelerate vascular disease, myocardial fibrosis, and malnutrition, contributing to high cardiovascular mortality in CKD populations. This systemic inflammation also impairs erythropoiesis, contributing to anemia of CKD.

• RAAS overactivation and vascular dysfunction: Intrarenal RAAS activation drives glomerular hypertension, proteinuria, inflammation, and fibrosis. Angiotensin II exerts direct nephrotoxic effects through AT1 receptor activation on glomerular cells, tubular cells, and fibroblasts, promoting TGF-β release and oxidative stress. Aldosterone contributes to sodium retention, hypertension, glomerular injury, and fibrosis. Systemic RAAS activation in CKD leads to progressive hypertension and loss of renal autoregulation, perpetuating glomerular injury. Endothelial dysfunction due to reduced nitric oxide bioavailability and increased endothelin activity impairs renal perfusion and protects against systemic hypertension.

• Diabetes mellitus (Type 1 and Type 2): Diabetic kidney disease is the leading cause of ESRD in developed countries, affecting 20-40% of diabetic patients. The pathophysiology involves hyperglycemia-driven podocyte injury, glomerular basement membrane thickening, and progressive glomerulosclerosis (both nodular Kimmelstiel-Wilson lesions and diffuse proliferative lesions). Hyperglycemia increases reactive oxygen species (ROS) production through mitochondrial respiration and NADPH oxidase activation, promotes non-enzymatic glycosylation of proteins (advanced glycation end products, AGEs), and activates pro-fibrotic pathways. Diabetic patients have higher systemic and intrarenal RAAS activation and frequently develop concurrent hypertension, amplifying renal injury. Screening for albuminuria/CKD is recommended in all diabetic patients at diagnosis (Type 2) or 5 years after diagnosis (Type 1).

• Hypertension: Systemic hypertension is the second leading cause of CKD and is present in >50% of CKD patients. Hypertension causes glomerular injury through mechanical stress (glomerular capillary hypertension), loss of renal autoregulation, endothelial dysfunction, and RAAS activation. Patients with hypertensive CKD typically show hypertensive arteriolosclerosis (acute/chronic arteriolar narrowing) with global glomerulosclerosis. The relationship between hypertension and CKD is bidirectional: hypertension causes CKD, and CKD causes hypertension through fluid retention, RAAS activation, and sympathetic activation. Control of blood pressure significantly slows CKD progression, making it a primary therapeutic target.

• Glomerulonephritis: Primary and secondary glomerulonephritides account for 10-15% of CKD cases. IgA nephropathy is the most common primary glomerulonephritis worldwide. Lupus nephritis is a major secondary cause in young women. Post-streptococcal glomerulonephritis typically follows streptococcal pharyngitis. ANCA-associated vasculitis (granulomatosis with polyangiitis, microscopic polyangiitis) causes rapidly progressive glomerulonephritis. Membranoproliferative glomerulonephritis (MPGN) is associated with hepatitis C and other infections. Diagnosis requires kidney biopsy with light, immunofluorescence, and electron microscopy examination, and early immunosuppressive therapy may halt or reverse progression in some forms.

• Polycystic kidney disease: Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited renal disease, caused by mutations in PKD1 (~85%) or PKD2 genes, affecting 1:400-1:1000 individuals. Progressive cyst development and rupture lead to interstitial inflammation, fibrosis, and ESRD in most PKD1 patients by age 50-60 years. PKD2 typically progresses more slowly. Autosomal recessive polycystic kidney disease (ARPKD) is rarer and more severe, often presenting in childhood. Management includes blood pressure control, avoidance of nephrotoxins, treatment of cyst-associated complications, and newer therapies targeting cAMP (tolvaptan).

• Chronic glomerulonephritis (secondary causes): Hepatitis C infection causes MPGN and cryoglobulinemic vasculitis. Hepatitis B can cause membranous nephropathy. HIV-associated nephropathy (HIVAN) typically causes focal segmental glomerulosclerosis (FSGS). Syphilis causes membranoproliferative glomerulonephritis. Chronic pyelonephritis from reflux nephropathy, obstructive uropathy, or recurrent infections leads to scarring and tubulointerstitial CKD. Systemic sclerosis (scleroderma renal crisis) causes acute kidney injury with associated microangiopathic hemolytic anemia.

• Drug-induced and toxic CKD: NSAIDs cause acute kidney injury and progressive CKD, particularly in volume-depleted states or with concomitant ACE inhibitor/ARB use. Aminoglycosides cause acute tubular necrosis (ATN) and chronic tubulointerstitial disease. Amphotericin B is nephrotoxic through tubular injury and vasoconstriction. ACE inhibitors and ARBs, while protective in many CKD patients, can cause acute kidney injury if used in specific settings (advanced CKD, bilateral renal artery stenosis, volume depletion). Contrast-associated acute kidney injury (CA-AKI) occurs from osmotic ATN and is now more commonly called contrast-associated nephropathy. Lithium causes chronic tubulointerstitial nephritis and nephrogenic diabetes insipidus. Cisplatin and other chemotherapy agents cause tubulointerstitial damage.

• Tubulointerstitial nephritis (TIN): Drug-induced TIN (particularly from NSAIDs, antibiotics like ampicillin and trimethoprim-sulfamethoxazole, proton pump inhibitors, and diuretics) accounts for 10-15% of acute kidney injury and can progress to CKD. Pyelonephritis from obstruction or reflux leads to chronic scarring. Uric acid nephropathy from massive cell turnover (tumor lysis syndrome) or chronic hyperuricemia causes crystal-induced tubulointerstitial damage. Contrast nephropathy causes tubular injury. Herbal remedies (aristolochic acid) cause Chinese herbs nephropathy with progressive tubulointerstitial fibrosis.

• Obstructive uropathy: Chronic obstruction from benign prostatic hyperplasia (BPH), prostate cancer, bladder outlet obstruction, or ureteral obstruction (kidney stones, tumors, fibrosis) leads to tubulointerstitial atrophy and progressive CKD. Relief of obstruction may partially recover renal function if obstruction is not prolonged; however, chronic obstruction results in irreversible damage.

• Cardiovascular disease and renal artery stenosis: Atherosclerotic renal artery stenosis (RAS) causes ischemic nephropathy, particularly in elderly patients with smoking history and diffuse atherosclerosis. Unilateral RAS reduces ipsilateral kidney perfusion; bilateral RAS or RAS in a solitary kidney can cause CKD. Aortic atherosclerosis with atheroemboli can cause acute kidney injury or progressive CKD. Congestive heart failure with chronic renal hypoperfusion leads to cardiorenal syndrome and progressive CKD.

• Metabolic and genetic causes: Hyperlipidemia (particularly elevated LDL cholesterol) contributes to glomerulosclerosis and tubulointerstitial disease. Chronic hyperuricemia from primary gout or secondary causes (high purine diet, cell turnover) causes uric acid crystal nephropathy. Cystic fibrosis patients develop CKD from cystic fibrosis-related diabetes and drug toxicity. Alport syndrome (mutations in genes encoding type IV collagen) causes progressive glomerulonephritis with characteristic splitting of glomerular basement membrane ("basket-weave" appearance on electron microscopy), sensorineural hearing loss, and ocular abnormalities. Thin basement membrane disease is a benign condition with microscopic hematuria and usually preserved renal function.

• Ethnicity and genetic factors: African Americans have higher rates of hypertensive CKD and FSGS; the APOL1 gene variant is associated with increased risk of CKD in African ancestry populations. Hispanic and Native American populations have higher prevalence of type 2 diabetes and associated CKD. Asians have higher prevalence of IgA nephropathy.

• Asymptomatic laboratory abnormalities: Most patients with CKD Stages 1-3 are identified incidentally on laboratory testing (elevated serum creatinine, reduced eGFR, or proteinuria during evaluation for other conditions). Albuminuria may be the only sign in early CKD, particularly in diabetes and hypertension. Urinalysis may reveal proteinuria, hematuria (suggesting glomerular disease), or white blood cells (suggesting infection or TIN). Progressive anemia may be noted on CBC without specific symptoms initially.

• Fatigue and weakness: Develop insidiously as renal anemia progresses due to reduced erythropoietin (EPO) production by peritubular fibroblasts and chronic inflammation. Anemia severity correlates with GFR decline, typically worsening in Stage 4-5 CKD. Patients describe reduced exercise tolerance, dyspnea on exertion, and generalized weakness. Orthostatic hypotension may occur if anemia is severe.

• Uremia and cognitive dysfunction: As GFR falls below 15 mL/min/1.73m² (Stage 5), accumulation of uremic solutes (urea, creatinine, phenols, indoles, polyamines) causes uremic syndrome. Cognitive dysfunction manifests as difficulty concentrating, memory problems, confusion, and in severe cases, altered mental status or uremic encephalopathy. Neuromuscular manifestations include restless leg syndrome, muscle cramps, tremor, and asterixis. These are partially reversible with dialysis initiation.

• Hypertension: Present in >90% of CKD patients and may be severe, contributing to further renal damage. Hypertension in CKD results from sodium and fluid retention (due to GFR decline), RAAS activation, sympathetic nervous system overactivity, and endothelial dysfunction. Patients may develop hypertensive urgency/emergency if blood pressure control is inadequate.

• Edema and fluid overload: Sodium and fluid retention occur as GFR declines, leading to peripheral edema (dependent, bilateral, pitting), pulmonary edema (orthopnea, paroxysmal nocturnal dy

Initial testing

• Serum creatinine with estimated GFR: report using the 2021 CKD-EPI creatinine equation, which deliberately omits a race coefficient. Creatinine is generated from muscle, so it overestimates GFR in cachectic, cirrhotic, amputee, and elderly patients.
• Spot urine albumin-to-creatinine ratio (UACR): preferred over dipstick and over 24-hour collection. A1 <30 mg/g, A2 30–300 mg/g, A3 >300 mg/g. Dipstick detects only albumin — order urine protein electrophoresis or a protein-to-creatinine ratio if myeloma light chains are suspected.
• Urinalysis with microscopy: dysmorphic RBCs and RBC casts point to glomerulonephritis; broad waxy casts indicate dilated, chronically damaged nephrons.

Confirmatory and staging steps

• Cystatin C–based eGFR: KDIGO recommends it to confirm a borderline creatinine-based eGFR (roughly the 45–59 range) before committing a patient to a CKD label, since cystatin C is independent of muscle mass.
• KDIGO heat map: stage by GFR category G1–G5 (G3 split into 3a and 3b) crossed with albuminuria category A1–A3. Prognosis is driven by both axes — G3a/A3 carries worse risk than G3b/A1.
• Renal ultrasound: small, echogenic kidneys with cortical thinning confirm chronicity. Kidneys are normal-sized or large despite advanced CKD in diabetic nephropathy, ADPKD, HIV-associated nephropathy, amyloidosis, and infiltrative disease.

Supporting findings of chronicity

• Normocytic anemia, hyperphosphatemia with elevated PTH, hypocalcemia, and a non-anion-gap (later high-anion-gap) metabolic acidosis all favor CKD over AKI.
• Kidney biopsy: reserved for unexplained decline, nephrotic-range proteinuria, or an active urine sediment suggesting a treatable glomerulonephritis; low yield once kidneys are small and fibrotic.

Slowing progression (KDIGO 2024 CKD guideline)

• RAAS inhibition: an ACE inhibitor or ARB (e.g., lisinopril, losartan) titrated to the maximum tolerated dose in any patient with CKD and albuminuria, with or without diabetes. It lowers intraglomerular pressure via efferent arteriolar dilation — expect a creatinine rise of up to about 30% and a small potassium rise; continue the drug. Never combine an ACE inhibitor with an ARB (hyperkalemia and AKI without benefit), and all ACE inhibitors/ARBs are contraindicated in pregnancy.
• SGLT2 inhibitors: dapagliflozin or empagliflozin added to RAAS blockade in albuminuric CKD regardless of diabetes status. They restore tubuloglomerular feedback, constricting the afferent arteriole. An initial "dip" in eGFR is expected and hemodynamic.
• Nonsteroidal MRA: finerenone in type 2 diabetes with albuminuric CKD, for its antifibrotic effect; monitor potassium.
• GLP-1 receptor agonists: semaglutide is endorsed by KDIGO and the ADA Standards of Care in type 2 diabetes with CKD for kidney and cardiovascular benefit.
• Blood pressure: KDIGO targets a systolic <120 mm Hg using standardized office measurement in most non-dialysis CKD.
• Glycemia and lipids: ADA targets an individualized A1c near 7%; metformin is safe to eGFR 30. KDIGO recommends a statin (or statin/ezetimibe) in CKD patients ≥50, but does not support initiating a statin de novo in dialysis patients.

Treating consequences

• Metabolic acidosis: oral sodium bicarbonate when serum bicarbonate is persistently low, as acidosis drives protein catabolism and bone loss.
• Anemia: repleteiron first, then an ESA (epoetin alfa) — do not target a normal hemoglobin; overshooting increases stroke and thrombosis.
• CKD-MBD: dietary phosphate restriction, non-calcium binders (sevelamer), activated vitamin D or calcimimetics (cinacalcet) for severe secondary hyperparathyroidism.
• Avoid: NSAIDs, unnecessary contrast, and nephrotoxic antimicrobials.

Emergencies

• Hyperkalemia: failure of distal potassium secretion, amplified by RAAS blockade, MRAs, and acidosis. Signaled by peaked T waves progressing to a widened QRS and sine wave. Give IV calcium gluconate first to stabilize the myocardium, then shift and remove potassium; dialysis if refractory.
• Uremic pericarditis: inflammation from retained uremic solutes; a pericardial friction rub with pleuritic chest pain and — classically — no diffuse ST elevation, because the visceral pericardium is spared. This is an absolute indication for urgent dialysis, not NSAIDs.
• Refractory pulmonary edema from sodium and water retention, unresponsive to loop diuretics as GFR falls.
• Calciphylaxis: medial calcification and thrombosis of dermal arterioles in advanced CKD-MBD, presenting as exquisitely painful retiform violaceous plaques that necrose; high mortality.

Chronic complications

• Cardiovascular disease: the leading cause of death in CKD, driven by LVH, accelerated arterial calcification, FGF23 excess, and inflammation. Most patients die of cardiovascular events before reaching dialysis.
• Anemia: reduced peritubular fibroblast erythropoietin plus hepcidin-mediated iron sequestration; normocytic, normochromic.
• CKD-MBD: hyperphosphatemia and calcitriol deficiency drive secondary hyperparathyroidism → osteitis fibrosa cystica (high turnover). Over-suppression of PTH produces adynamic bone disease with low turnover and increased fracture and calcification risk.
• Uremic bleeding: platelet dysfunction from uremic toxins; prolonged bleeding time with a normal platelet count and normal PT/PTT. Treat with desmopressin (DDAVP) or dialysis.
• Metabolic acidosis with muscle wasting and bone demineralization.

Treatment-related

• ACE inhibitor/ARB: hyperkalemia and AKI, particularly with volume depletion or bilateral renal artery stenosis.
• SGLT2 inhibitors: genital mycotic infection, volume depletion, euglycemic DKA.
• ESAs: hypertension, stroke, and thrombosis when hemoglobin is pushed toward normal.
• Calcium-based binders: positive calcium balance and vascular calcification.
• Dialysis access: catheter-related bacteremia; steal syndrome and high-output failure with AV fistulas; dialysis disequilibrium syndrome from rapid urea clearance and cerebral edema.

• Chronicity requires ≥3 months. A one-off creatinine is AKI. The single best next step for an isolated abnormal eGFR is to repeat it, plus a spot UACR — not imaging, not biopsy.
• Small echogenic kidneys = chronic. The exceptions with normal or enlarged kidneys are diabetic nephropathy, ADPKD, HIV-associated nephropathy, amyloidosis. This is the classic distinguishing question.
• Stage on two axes. KDIGO grades G1–G5 and A1–A3. A patient with eGFR 55 and UACR 500 mg/g is high-risk despite "only" G3a — the common distractor is staging by GFR alone.
• Creatinine rising ~30% after starting an ACE inhibitor is expected, reflecting efferent arteriolar dilation. Continue the drug; check potassium. A larger or progressive rise raises suspicion for bilateral renal artery stenosis.
• SGLT2 inhibitors are indicated in albuminuric CKD whether or not the patient has diabetes (KDIGO 2024) — the frequent trap is withholding them because glucose is normal or because eGFR is modestly reduced.
• Uremic pericarditis and refractory hyperkalemia, acidosis, or volume overload are dialysis indications — not the eGFR value itself. "Start dialysis when eGFR <15" is a distractor.
• Uremic bleeding: prolonged bleeding time with normal platelet count, PT, and PTT. Treat with DDAVP (releases von Willebrand factor multimers), cryoprecipitate, or dialysis — never platelet transfusion alone.
• Anemia of CKD is erythropoietin deficiency, but check and replete iron before starting an ESA, and do not target a normal hemoglobin — normalizing it increases stroke and thrombosis (KDIGO anemia guidance).
• Avoid gadolinium-based contrast in advanced CKD because of nephrogenic systemic fibrosis; metformin, by contrast, is acceptable down to eGFR 30 per ADA.