Gagal Ginjal Kronik (CKD)

01Pathophysiology

CKD is defined as a structural or functional kidney abnormality persisting for three or more months, with or without a decrease in eGFR below 60 mL/min/1.73m${}^2^2$. The key to understanding the vignette is recognizing that CKD is not a single disease but a final common pathway of many insults converging on irreversible nephron loss.

When nephrons are lost (from diabetes, hypertension, or glomerulonephritis), the remaining nephrons undergo adaptive hyperfiltration. Each surviving glomerulus increases its single-nephron GFR to compensate, which is why patients with mild CKD often have near-normal serum creatinine. This is a critical concept: creatinine does not rise noticeably until roughly 50% of renal function is already lost. This is why a vignette that describes a patient with "normal creatinine" does not rule out early kidney disease.

However, this adaptive hyperfiltration is itself maladaptive over time. The elevated intraglomerular pressure causes endothelial injury, podocyte damage, and eventual glomerulosclerosis (fibrosis of the glomerulus). Proteinuria worsens, and a vicious cycle ensues where proteinuria itself damages the tubulointersitium, accelerating fibrosis. This explains why proteinuria is both a marker and a driver of disease progression, and why reducing proteinuria with ACE-inhibitors or ARBs is a central therapeutic strategy.

As GFR progressively declines, the kidney loses its ability to maintain homeostasis. The consequences unfold in a predictable sequence that directly maps to clinical findings:

Decreased erythropoietin production leads to normocytic normochromic anemia, which becomes clinically apparent when eGFR falls below 60 mL/min/1.73m${}^2^2$, particularly in diabetics. This is not iron-deficiency anemia (which would be microcytic), and this distinction is a common testing point.

Impaired phosphate excretion causes hyperphosphatemia, which drives down ionized calcium and triggers secondary hyperparathyroidism. The kidneys also fail to convert 25-hydroxyvitamin D to its active form (1,25-dihydroxyvitamin D / calcitriol), further reducing calcium absorption. PTH rises to compensate, causing osteitis fibrosa cystica (high-turnover bone disease). This cascade is called CKD-Mineral Bone Disorder (CKD-MBD), and calcitriol levels notably begin to drop when eGFR falls below 40 mL/min/1.73m${}^2^2$.

Impaired acid excretion produces a non-anion-gap metabolic acidosis in early CKD (from defective ammoniagenesis), progressing to a high-anion-gap metabolic acidosis in advanced disease (from retained uremic toxins such as sulfates and phosphates). Serum bicarbonate tends to stabilize between 12-20 mEq/L and rarely falls below 10 mEq/L.

Impaired potassium excretion causes hyperkalemia, especially in the setting of oliguria, high dietary potassium intake, tissue breakdown, or hypoaldosteronism. The use of ACE-inhibitors or ARBs further exacerbates hyperkalemia, which is why monitoring potassium one week after starting or escalating these medications is essential.

Impaired sodium and water excretion leads to fluid overload, hypertension, and pulmonary edema, particularly when eGFR drops below 10-15 mL/min/1.73m${}^2^2$. However, even patients with mild-to-moderate CKD are vulnerable to sudden sodium loading.

In end-stage disease (eGFR <15 mL/min/1.73m${}^2^2$), the accumulation of uremic toxins produces the uremic syndrome: encephalopathy (confusion progressing to seizures and coma), peripheral neuropathy (restless legs, burning feet), pericarditis, platelet dysfunction (uremic bleeding), sexual dysfunction, and severe malnutrition.

02Classification and Clinical Manifestation

CKD Staging by GFR (KDIGO)

Note: G1 and G2 require additional evidence of kidney damage (proteinuria, hematuria, structural abnormality) to qualify as CKD. A GFR of 70 mL/min/1.73m${}^2^2$ alone without any marker of damage is NOT CKD.

Albuminuria Categories (Persistent)

KDIGO Risk Stratification (Prognosis Heat Map)

The combination of GFR stage and albuminuria category determines the risk of disease progression and monitoring frequency:

Progression Criteria

According to the PNPK Gagal Ginjal Kronis 2023, CKD progression is defined as a drop in GFR category accompanied by a 25% or greater decrease in eGFR from baseline. Rapid progression is defined as a sustained decline of more than 5 mL/min/1.73m${}^2^2$ per year.

Clinical Manifestations by Complication

Pediatric Considerations

In children, eGFR is calculated using the Schwartz formula:

$$eGFR=\frac{k\times \text{Height (cm)}}{\text{Serum Creatinine (mg/dL)}}eGFR\; =\; \backslash frac\{k\; \backslash times\; \backslash text\{Height\; (cm)\}\}\{\backslash text\{Serum\; Creatinine\; (mg/dL)\}\}$$

Where $kk$ values are: 0.33 (preterm neonates), 0.45 (term neonates), 0.55 (children 1-13 years and girls >13), 0.70 (boys >13 years).

03Diagnostic Workup

The first step in evaluating for CKD is a urinalysis. This is the screening-level test that picks up proteinuria, hematuria, and cellular casts. A positive dipstick for protein or blood triggers further workup.

The best initial test for assessing kidney function is a serum creatinine with calculated eGFR using the CKD-EPI formula. According to the PNPK Gagal Ginjal Kronis 2023, if the initial eGFR is <60 mL/min/1.73m${}^2^2$, the measurement must be repeated in 12 weeks (3 months). Two values below 60 mL/min/1.73m${}^2^2$ separated by at least 3 months establish the diagnosis of CKD. A single low value could represent acute kidney injury, not chronic disease, and this distinction is commonly tested.

Similarly, for proteinuria: the urine albumin-creatinine ratio (ACR) must be positive ($\ge \backslash geq$30 mg/g) on two separate occasions 3 months apart to be called persistent albuminuria. A first-morning urine sample is preferred because it minimizes the variability of urine concentration.

Renal ultrasound is indicated when eGFR is below 60 mL/min/1.73m${}^2^2$ with persistent proteinuria, when there is progressive decline in renal function, when urinary tract obstruction is suspected, when renal artery stenosis is suspected (Doppler ultrasound), or when there is a family history of polycystic kidney disease. The classic finding in CKD is bilateral small, echogenic kidneys. Notable exceptions to the "small kidneys" rule include diabetic nephropathy, amyloidosis, HIV-associated nephropathy, and polycystic kidney disease, all of which may present with normal or enlarged kidneys.

Kidney biopsy is the most accurate test (gold standard) for determining the underlying etiology of CKD. It is not performed in every patient but is reserved for cases where the diagnosis is unclear and the result would change management.

An important workup principle: for patients with hematuria, always rule out urinary tract infection first. Patients with persistent hematuria without proteinuria or GFR decline should be referred to urology (to rule out malignancy). Patients with hematuria plus hypertension, proteinuria, or declining GFR should be referred to nephrology (suggesting glomerular hematuria).

Referral Criteria to Nephrology

The PNPK Gagal Ginjal Kronis 2023 clearly states that patients should be referred to nephrology when: (1) eGFR <30 mL/min/1.73m${}^2^2$ (Stage 4-5); (2) sustained eGFR decline from a baseline of 60 (drop >5 mL/min/1.73m${}^2^2$ in 6 months); (3) suspected glomerular hematuria; (4) uncontrolled hypertension with CKD; (5) suspected renal artery stenosis; (6) hereditary kidney disease; (7) persistent potassium abnormalities; (8) recurrent kidney stones; (9) renal anemia with Hb <10 g/dL; (10) secondary hyperparathyroidism.

04Management & Treatment

Step 1: Identify and treat reversible causes. Before labeling a patient as having progressive CKD, the PNPK Gagal Ginjal Kronis 2023 emphasizes ruling out AKI superimposed on CKD. Common reversible causes include: hypovolemia (dehydration, diuretics, bleeding), hypotension (cardiac or pericardial disease), sepsis, nephrotoxic drugs (NSAIDs, aminoglycosides, IV contrast), and urinary tract obstruction. A vignette describing sudden worsening of kidney function in a stable CKD patient should prompt you to search for these causes before attributing the decline to disease progression.

Step 2: Blood pressure control. For most adults with pre-dialysis CKD, the target systolic blood pressure is <120 mmHg. For post-transplant patients, the target is <130/80 mmHg. First-line therapy in CKD patients with proteinuria is an ACE inhibitor or ARB, which must be titrated to the maximum tolerated dose. This class is critical because it reduces intraglomerular pressure (by dilating the efferent arteriole), thereby reducing proteinuria and slowing progression. Serum potassium and eGFR must be checked one week after starting or dose-escalating an ACE-i/ARB. The combination of ACE-i + ARB, or either with a direct renin inhibitor (DRI), is explicitly contraindicated. In renal transplant recipients, the preferred first-line agents are dihydropyridine CCBs or ARBs. Sodium intake should be restricted to <2 g/day (equivalent to <5 g NaCl/day).

Step 3: Slow progression with SGLT2 inhibitors. SGLT2 inhibitors (e.g., dapagliflozin, empagliflozin) provide additional renoprotection for CKD patients with proteinuria, with or without diabetes. They reduce glomerular hyperfiltration by activating tubuloglomerular feedback.

Step 4: Glycemic control for diabetic CKD. The target HbA1c is individualized, ranging from <6.5% to <8.0%. The recommended approach per the guideline is: start with metformin (if eGFR $\ge \backslash geq$30 mL/min/1.73m${}^2^2$), add SGLT2 inhibitor next, and then add a long-acting GLP-1 receptor agonist if glycemic targets are not met.

Step 5: Dietary management. Protein restriction slows CKD progression. For non-diabetic CKD stages 3-5 not on dialysis: 0.55-0.60 g/kg/day, or a very low protein diet of 0.28-0.43 g/kg/day supplemented with keto acid/amino acid analogues. For diabetic CKD stages 3-5: 0.6-0.8 g/kg/day. Sodium restriction of <2.3 g/day helps control blood pressure and fluid overload.

Step 6: Manage complications.

• Metabolic acidosis: Maintain serum bicarbonate at 24-26 mmol/L with oral bicarbonate supplementation. Correcting acidosis also slows CKD progression.

• Hyperkalemia: Two therapeutic principles apply: (1) redistribute potassium intracellularly using insulin with glucose, beta-2 agonists, or sodium bicarbonate, and (2) remove potassium from the body via diuretics, potassium binders (sodium polystyrene sulfonate), or dialysis. Always evaluate for contributing medications (NSAIDs, non-selective beta-blockers, ACE-i/ARB).

• Anemia: Always replete iron before starting ESA. Iron deficiency is defined as transferrin saturation <20% and/or ferritin <100 ng/mL (non-HD/peritoneal dialysis) or <200 ng/mL (hemodialysis). IV iron dosing is 100 mg per session at intervals based on ferritin level (every 2 weeks for ferritin <200; every 4 weeks for 200-300; every 6 weeks for 301-500). ESA (erythropoietin, darbepoetin) is initiated after iron repletion. The Hb target on ESA should NOT exceed 13 g/dL, as exceeding this threshold increases the risk of cardiovascular events, stroke, and death. This is one of the most tested facts about CKD anemia management.

• CKD-MBD: Restrict dietary phosphate, add oral phosphate binders (calcium carbonate, calcium acetate, or sevelamer), and supplement with cholecalciferol or ergocalciferol to correct 25(OH)D deficiency. Calcitriol or vitamin D analogues can be used to directly suppress PTH. Total elemental calcium intake (dietary + supplements + binders) should be 800-1000 mg/day for CKD stages 3-4. Excess calcium supplementation increases the risk of coronary artery calcification.

• Dyslipidemia: For adults $\ge \backslash geq$50 years with CKD and eGFR <60 (G3a-G5, non-dialysis): statin or statin/ezetimibe. For adults $\ge \backslash geq$50 years with eGFR $\ge \backslash geq$60: statin alone. Do NOT initiate statin in patients already on dialysis, but continue if previously started. For hypertriglyceridemia: lifestyle modification is the primary recommendation.

Step 7: Prepare for renal replacement therapy. Patients reaching CKD Stage 4 (eGFR <30 mL/min/1.73m${}^2^2$) should receive pre-dialysis education and be counseled on options: hemodialysis, peritoneal dialysis, or kidney transplantation. Vascular access planning (preferably arteriovenous fistula) should begin at eGFR 15-20 mL/min/1.73m${}^2^2$.

Step 8: Initiate dialysis when indicated. According to the PNPK Gagal Ginjal Kronis 2023, dialysis should be started when one or more of the following are present: (1) signs/symptoms caused by kidney failure (serositis, acid-base or electrolyte abnormalities, pruritus); (2) inability to control volume status or blood pressure; (3) progressive malnutrition refractory to dietary intervention; (4) cognitive impairment. These events often (but not always) occur at an eGFR between 5 and 10 mL/min/1.73m${}^2^2$. Importantly, the IDEAL trial demonstrated no survival benefit from early dialysis initiation (eGFR 10-14) versus late initiation (eGFR 5-7), confirming that the decision should be symptom-driven, not GFR-driven.

05Differential Diagnosis & Distractors

06Traps & High-Yield Pearls

Trap 1: Confusing a single elevated creatinine with CKD. The most common mistake is diagnosing CKD based on a single abnormal value. The definition requires persistence for at least 3 months. A patient presenting with a newly elevated creatinine requires repeat testing in 12 weeks. If the vignette specifies "labs from 4 months ago also showed creatinine of 2.1," that is the clue confirming chronicity.

Trap 2: Missing AKI on CKD. When a CKD patient shows sudden deterioration, the instinct may be to accept it as disease progression. Always look for reversible causes (new NSAID, dehydration, obstruction, contrast exposure). The "next best step" in this scenario is to treat the reversible cause, not to start dialysis.

Trap 3: Initiating dialysis by eGFR alone. The IDEAL trial is critical background. There is no survival benefit to starting dialysis at eGFR 10-14 vs. 5-7. The indication for dialysis is symptomatic uremia (refractory fluid overload, pericarditis, encephalopathy, bleeding, malnutrition), not a particular eGFR threshold. A vignette describing a patient with eGFR of 12 who is asymptomatic does not require dialysis yet.

Trap 4: Overshooting the Hb target with ESA. Targeting Hb above 13 g/dL increases cardiovascular mortality. The correct action when Hb rises above target is to reduce the ESA dose, not stop it entirely. Also, always ensure iron stores are adequate before starting ESA; giving ESA to an iron-depleted patient is both ineffective and a common wrong answer.

Trap 5: Combining ACE-i + ARB. This is explicitly contraindicated. Vignettes may present a patient with persistent proteinuria despite maximal ACE-i, tempting students to add an ARB. The correct answer is to add an SGLT2 inhibitor, NOT a second RAS blocker.

Trap 6: Forgetting the statin rules for dialysis patients. Do NOT initiate statin in a patient who starts dialysis without previously being on one. However, if the patient was already on a statin before dialysis initiation, continue it.

Trap 7: Assuming CKD kidneys are always small. Bilateral small echogenic kidneys is the classic ultrasound finding, but several conditions produce CKD with normal or enlarged kidneys: diabetic nephropathy, amyloidosis, HIV-associated nephropathy, polycystic kidney disease, and early CKD of any cause. A vignette describing a diabetic with CKD and "normal-sized kidneys" is not a contradiction.

The core competency being tested across CKD questions is your ability to (1) classify the stage correctly using both eGFR and albuminuria, (2) sequence the workup logically (urinalysis first, then quantify proteinuria, then image, then biopsy if needed), (3) choose the right medications in the right order (ACE-i/ARB then SGLT2i, iron before ESA, not statin for new dialysis patients), and (4) recognize when to initiate dialysis based on clinical indications rather than a lab number.