Kidney Function Tests and Pathophysiology of Renal Failure

Introduction

Assessment of kidney function provides vital information about glomerular filtration, tubular integrity, and overall renal health. Understanding renal function tests helps in early detection of kidney disorders, while knowledge of renal failure is essential for recognizing life-threatening complications such as electrolyte imbalance and fluid overload.

Kidney Function Tests

• Kidney function tests evaluate the ability of the kidneys to filter blood, reabsorb essential substances, and excrete metabolic waste products.
• Physiologically, these tests are broadly classified into glomerular function tests and tubular function tests.
• Glomerular function tests assess the efficiency of filtration.
• Common tests include measurement of blood urea, serum creatinine, and estimation of glomerular filtration rate using clearance techniques.
• Creatinine clearance is widely used in clinical practice to assess renal function.
• Estimation of urinary protein excretion helps detect glomerular injury.
• Para-aminohippurate clearance has been used to estimate renal plasma flow.
• Tubular function tests evaluate reabsorption, secretion, and urine-concentrating ability.
• These include concentration and dilution tests, assessment of urinary acidification, and evaluation of renal handling of electrolytes and amino acids.
• Measurement of urine and plasma osmolality provides useful information regarding tubular performance.
• Clinically, kidney function tests are often grouped into four categories:
  • Routine tests: Urinalysis, blood urea nitrogen, serum creatinine, and serum electrolyte measurements.
  • Further assessment tests: Clearance studies and concentration–dilution tests.
  • Specific tests: Evaluation of renal acidification, sodium handling, and renal plasma flow.
  • Imaging studies: Ultrasonography, computed tomography, and magnetic resonance imaging.
• Together, these investigations provide a comprehensive assessment of renal structure and function and aid in the diagnosis and monitoring of kidney diseases.

Routine Urine Analysis

• Routine urinalysis is a fundamental investigation used to assess kidney function and detect systemic diseases that affect the urinary system.
• It includes evaluation of both physical and biochemical properties of urine.

Physical Characteristics

Volume

• Urine volume is an important indicator of renal function and hydration status.
• Normal urine output in adults is approximately 1–2 liters per day, depending on fluid intake and physiological conditions.
• Increased urine output may occur with excessive fluid intake, diuretic therapy, diabetes mellitus, diabetes insipidus, and certain chronic kidney disorders.
• Reduced urine output may be seen in dehydration, excessive sweating, hypovolemia, hypotension, shock, edema-forming states, and acute kidney injury.

Oliguria and Anuria

• Oliguria refers to a marked reduction in urine output, generally less than 400–500 milliliters per day in adults.
• Such low urine volume may be insufficient for adequate excretion of metabolic waste products.
• Anuria is defined as an almost complete absence of urine production, usually less than 100 milliliters per day.
• It is a serious clinical condition requiring urgent evaluation.
• Oliguria and anuria may result from reduced urine formation within the kidneys.
• Common renal causes include acute kidney injury, severe glomerular diseases, and renal vascular disorders.
• They may also occur because of urinary tract obstruction.
• Obstructive causes include urinary calculi, prostatic enlargement, urethral strictures, neurogenic bladder dysfunction, and pelvic masses compressing the urinary tract.
• Careful assessment of urine volume provides valuable information regarding renal perfusion, glomerular filtration, and overall kidney health.

Polyuria

• Polyuria is defined as urine output exceeding approximately 3 liters per day in adults.
• It may result from water diuresis or osmotic diuresis.
• Common causes include excessive fluid intake, uncontrolled diabetes mellitus with glycosuria, hypercalcemia, diabetes insipidus, diuretic therapy, and psychogenic polydipsia.
• Nephrogenic diabetes insipidus may occur due to tubular disorders, chronic tubulointerstitial disease, hypokalemia, hypercalcemia, or drugs such as lithium.
• Increased urinary frequency due to lower urinary tract disorders should be distinguished from true polyuria, as total urine volume may remain normal.

Nocturia

• Nocturia refers to waking during sleep to pass urine.
• It may occur because of increased urine production, excessive evening fluid intake, use of diuretics, chronic kidney disease, benign prostatic enlargement, or sleep disorders.
• Persistent nocturia warrants evaluation for underlying systemic or urinary tract disease.

Appearance

• Normal urine is usually clear and transparent.
• Turbidity may develop on standing because bacterial degradation of urea increases urine alkalinity, promoting precipitation of phosphate salts.
• Cloudy urine may also result from urinary tract infection, excess phosphate crystals, or the presence of lymphatic fluid in urine.

Odor

• Urine normally has a faint aromatic odor.
• Stored urine develops an ammoniacal smell due to bacterial conversion of urea into ammonia.
• In diabetic ketoacidosis, urine may have a characteristic fruity odor caused by ketone bodies, particularly acetone.
• Certain medications and dietary substances can also alter urine odor.

Color

• Normal urine color ranges from pale yellow to amber because of the pigment urochrome.
• Dark yellow urine may occur with bilirubinuria.
• Brown or black urine may be seen in alkaptonuria or melanuria.
• Red or reddish-brown urine may result from hematuria, hemoglobinuria, myoglobinuria, porphyrias, or certain drugs such as rifampicin.

Specific Gravity

• Normal specific gravity ranges from approximately 1.005 to 1.030.
• It reflects the concentration of dissolved substances in urine and correlates roughly with urine osmolality.
• Specific gravity decreases in dilute urine, such as in diabetes insipidus, and increases during dehydration.
• Glucose, proteins, and radiographic contrast agents can falsely elevate specific gravity.
• In advanced chronic kidney disease, urine specific gravity may become fixed near 1.010, a condition known as isosthenuria.

Biochemical Characteristics

Reaction of Urine

• Urine pH is an important biochemical indicator of renal function and systemic acid–base status.
• Normal urine is usually mildly acidic, with an average pH of about 6.0 and a typical range of 4.5–8.0.
• Following a mixed meal, urine may become temporarily alkaline because gastric acid secretion increases bicarbonate entry into the bloodstream, a phenomenon known as the alkaline tide.
• Diet significantly influences urine pH.
• Protein-rich diets increase acid production and tend to acidify urine.
• Diets rich in fruits and vegetables promote bicarbonate generation and often produce alkaline urine.
• Persistently alkaline urine may occur in urinary tract infections caused by urease-producing bacteria, during carbonic anhydrase inhibitor therapy, after alkali ingestion, or in certain forms of renal tubular acidosis.
• Proteinuria refers to abnormal excretion of proteins in urine and is an important marker of kidney disease.
• The glomerular filtration barrier normally restricts the passage of most plasma proteins, especially larger molecules.
• Damage to the glomerular filtration membrane increases protein permeability and results in proteinuria.
• Albumin is the predominant protein detected because it is smaller and more readily filtered than most plasma globulins.
• Hemoglobin may appear in urine during intravascular hemolysis, producing hemoglobinuria.
• Small quantities of protein are normally present in urine because of tubular secretion and shedding of epithelial proteins.
• Normal total urinary protein excretion is usually less than 150 milligrams per day, and routine urinalysis may not detect these trace amounts.
• Persistent proteinuria requires further evaluation because it may indicate underlying glomerular disease, diabetic kidney disease, or other renal disorders.

Table 82.1: 24-hr urinary protein and protein-creatinine ratio in different conditions.

24-Hour Urinary Protein (g/day)	Protein–Creatinine Ratio (mg/mmol)	Clinical Interpretation
<0.03	<2.5 (males), <3.5 (females)	Normal protein excretion
0.03–0.30	3.5–15	Moderately increased albuminuria
0.30–0.50	15–50	Overt proteinuria; often dipstick positive
>2.5	>250	Suggestive of significant glomerular injury
>4.0	>400	Severe proteinuria, strongly indicative of glomerular disease

Protein-Creatinine Ratio

• The protein–creatinine ratio in a random urine sample provides a convenient estimate of daily urinary protein excretion.
• Normal values are generally less than 2.5 mg/mmol in males and 3.5 mg/mmol in females.
• Higher values suggest abnormal protein loss and warrant further evaluation for kidney disease.

Proteinuria

• Proteinuria refers to excessive protein excretion in urine.
• It may occur in glomerular diseases, tubular disorders, urinary tract infections, heart failure, pre-eclampsia, and after vigorous physical exercise.
• Proteinuria develops when glomerular filtration of proteins increases or when tubular reabsorption of filtered proteins is impaired.
• Common laboratory methods for detection include dipstick testing and quantitative protein estimation.

Bence-Jones Proteinuria

• Bence–Jones proteinuria results from urinary excretion of monoclonal immunoglobulin light chains.
• These proteins are produced by abnormal plasma cells and are readily filtered by the kidneys.
• Bence–Jones proteins are classically associated with multiple myeloma and other plasma cell dyscrasias.
• Detection of these proteins is clinically valuable for diagnosis, monitoring disease activity, and assessing renal involvement.

Microalbuminuria

• Microalbuminuria refers to urinary albumin excretion of 30–300 mg per day or moderately increased albumin excretion.
• It is an early indicator of glomerular injury and may precede overt proteinuria.
• Regular screening is recommended in patients with diabetes because it helps detect early diabetic kidney disease.
• Persistent microalbuminuria is also associated with an increased risk of cardiovascular disease and adverse vascular outcomes.

Blood in Urine

• Hematuria is the presence of red blood cells in urine.
• It may be microscopic or visible to the naked eye.
• Hematuria suggests bleeding anywhere along the urinary tract.
• Common causes include glomerulonephritis, urinary tract trauma, calculi, infections, and malignancy.

Hemoglobinuria and Myoglobinuria

• Hemoglobinuria indicates free hemoglobin in urine and is usually associated with intravascular hemolysis.
• Myoglobinuria results from myoglobin release during skeletal muscle injury, particularly rhabdomyolysis.
• Both conditions may cause dark-colored urine and can contribute to acute kidney injury.

Reducing Sugars in Urine

• Glucosuria refers to the presence of glucose in urine.
• Under normal conditions, filtered glucose is almost completely reabsorbed by the proximal tubule and is absent from urine.
• Glucosuria commonly occurs when blood glucose exceeds the renal threshold, typically around 180 mg/dL, as in diabetes mellitus.
• Urinary glucose can be detected by biochemical screening tests such as Benedict’s test.
• Causes of glucosuria include:
  • Diabetes mellitus, the most common cause.
  • Renal glucosuria, resulting from impaired tubular glucose reabsorption despite normal blood glucose levels.
  • Transient postprandial glucosuria due to a temporary rise in blood glucose after meals.
  • Conditions associated with rapid glucose absorption, such as after gastric surgery.
  • Hyperthyroidism and certain hepatic disorders.

• Mild glucosuria may occur during pregnancy because increased glomerular filtration lowers the renal threshold for glucose.
• However, gestational diabetes should always be excluded when glucosuria is detected in pregnant women.

Other Biochemical Tests

Ketone Bodies in Urine

• The three ketone bodies are acetoacetate, beta-hydroxybutyrate, and acetone.
• The presence of ketone bodies in urine is termed ketonuria.
• Ketone bodies are normally absent or present only in negligible amounts in urine.
• Ketonuria occurs when fat metabolism increases because of inadequate carbohydrate utilization.
• It is commonly observed in uncontrolled diabetes mellitus, prolonged fasting, starvation, persistent vomiting, and ketogenic diets.
• Urinary ketone bodies can be detected by Rothera’s test and Gerhardt’s test.

Bile Salts in Urine

• Bile salts may appear in urine during the early stages of obstructive jaundice.
• Their presence indicates impaired bile flow from the liver to the intestine.
• Detection of urinary bile salts is useful in the evaluation of hepatobiliary disorders.
• Hay’s test and Pettenkofer’s test are commonly used for their detection.

Bile Pigments in Urine

• The principal bile pigments are bilirubin and biliverdin.
• Bilirubin normally does not appear in urine because unconjugated bilirubin is not water soluble.
• Urinary bilirubin is usually present in obstructive jaundice and hepatocellular disease.
• Detection of bilirubinuria helps differentiate causes of jaundice.
• Modified van den Bergh reaction and Fouchet’s test are used to detect urinary bilirubin.

Urobilinogen in Urine

• Urochrome is the major pigment responsible for the normal yellow color of urine.
• Small amounts of urobilinogen are normally excreted in urine.
• Urinary urobilinogen increases in hemolytic disorders, liver diseases, persistent fever, and some biliary tract disorders.
• Ehrlich’s test and Schlesinger’s test are commonly used for its detection.

Measurement of (NPN) in Urine

• Non-protein nitrogen compounds include urea, creatinine, and uric acid.
• These metabolites are eliminated primarily through the kidneys.
• Urinary creatinine measurement is useful for assessing renal function and estimating creatinine clearance.
• Urinary urea levels vary with dietary protein intake, hydration status, and metabolic conditions; therefore, they are not a specific indicator of kidney function.
• Blood urea concentration provides a more reliable assessment of renal function.
• Urinary uric acid excretion increases in conditions associated with enhanced purine metabolism and cellular breakdown.

Clearance Tests

• Clearance is the volume of plasma from which a substance is completely removed by the kidneys per unit time and is expressed in milliliters per minute.
• Clearance testing is primarily used to evaluate glomerular filtration rate, which is an important indicator of renal function and the severity of kidney disease.
• The clearance of a substance depends on:
  • Its concentration in urine.
  • Its concentration in plasma.
  • The rate of urine formation per minute.

• Clearance is calculated by determining the amount of a substance excreted in urine and relating it to its plasma concentration.
• A substance that is freely filtered at the glomerulus and is neither reabsorbed nor secreted by the renal tubules provides the most accurate measurement of glomerular filtration rate.
• Inulin clearance is considered the reference method for measuring glomerular filtration rate because inulin undergoes filtration without tubular reabsorption or secretion.
• Creatinine clearance is commonly used in clinical practice to estimate glomerular filtration rate because it is simple, practical, and reasonably accurate.
• Urea clearance may also be used to assess renal function, although its value is influenced by tubular reabsorption and hydration status.
• A substance that is filtered and actively secreted by the tubules, with minimal reabsorption, can be used to estimate renal plasma flow.
• Para-aminohippuric acid clearance is traditionally used for measurement of effective renal plasma flow.
• In healthy adults, renal plasma flow is approximately 600–700 mL/min, while glomerular filtration rate is about 120–125 mL/min.
• The proportion of renal plasma flow that becomes glomerular filtrate is called the filtration fraction.
• The normal filtration fraction is approximately 20%, indicating that about one-fifth of the plasma entering the kidneys is filtered through the glomeruli.
• Clearance tests provide valuable information for assessing glomerular function, monitoring kidney disease progression, and evaluating the effectiveness of treatment.

Table 82.2: Relationship between GFR and clearance value.

Renal Handling of Substance	Clearance Relative to Glomerular Filtration Rate	Example
Filtered only; neither reabsorbed nor secreted	Equals glomerular filtration rate	Inulin
Filtered and partially reabsorbed	Less than glomerular filtration rate	Urea
Filtered and secreted without significant reabsorption	Greater than glomerular filtration rate	Para-aminohippuric acid (PAH)
Filtered with both reabsorption and secretion	Variable; depends on net tubular transport	Uric acid

Blood Investigations

• Blood investigations are important for evaluating renal function and detecting electrolyte disturbances.
• Common tests include serum urea, creatinine, uric acid, sodium, and potassium measurements.

Serum Urea

• Normal serum urea concentration is approximately 15–40 mg/dL.
• Elevated serum urea may result from high protein intake, gastrointestinal bleeding, tissue injury, severe infections, dehydration, or reduced renal excretion.

Serum Creatinine

• Serum creatinine is a more specific indicator of glomerular filtration than urea.
• Normal serum creatinine levels are about 0.7–1.3 mg/dL in males and 0.5–1.1 mg/dL in females.
• Increased creatinine occurs in renal impairment, rhabdomyolysis, or with certain medications.

Serum Electrolytes

• Normal serum sodium is 136–145 mmol/L, and potassium is 3.5–5.0 mmol/L.
• Hyperkalemia is a significant finding in advanced renal dysfunction.

Tubular Function Tests

• Tubular function tests assess the ability of renal tubules to reabsorb water and solutes from tubular fluid.
• Measurement of urine specific gravity is a simple method for evaluating tubular concentrating capacity.

Determination of Specific Gravity

• Specific gravity reflects the total concentration of dissolved substances in urine.
• Urine osmolality measures the concentration of osmotically active particles.
• In proteinuria, specific gravity may increase markedly because proteins contribute to urine density, whereas osmolality rises only slightly.
• Interpretation of both parameters helps assess tubular function and urine concentration.

Other Tests

Tubular functions are determined by concentration and dilution tests. The earliest manifestation of the renal disease is the inability to concentrate urine. This is detected by concentration test.

Concentration Test

• Tubular function tests evaluate the ability of renal tubules to concentrate and dilute urine appropriately.
• Impaired urinary concentrating ability is often one of the earliest detectable abnormalities in kidney disease.
• The concentration test assesses the kidney’s capacity to conserve water during a period of restricted fluid intake.
• In this test, fluid intake is restricted overnight, and a morning urine sample is collected for analysis.
• Urine specific gravity is measured to determine the concentrating ability of the kidneys.
• A specific gravity greater than approximately 1.020–1.025 after water deprivation generally indicates adequate tubular function.
• Persistently low specific gravity despite fluid restriction suggests impaired tubular reabsorption of water and reduced concentrating capacity.
• Interpretation of results should consider hydration status, medications, and associated medical conditions.

Determination of Urine Volume

• Measurement of twenty-four-hour urine volume provides additional information about tubular function.
• Normal daily urine output in adults is usually about 1–2 liters, depending on fluid intake and physiological conditions.
• Under normal circumstances, daytime urine production exceeds nighttime urine production.
• Excessive urine output during the night, known as nocturnal polyuria, may indicate early tubular dysfunction or impaired renal concentrating ability.
• Evaluation of urine volume, specific gravity, and osmolality together provides a more reliable assessment of tubular function than any single measurement alone.
• These tests are useful for detecting early renal tubular disorders and monitoring disease progression.

Measurement of Osmolality

• Urine osmolality reflects the concentration of dissolved particles in urine and provides important information about renal tubular function.
• Normal urine osmolality varies widely, typically from about 50 to 1200 mOsm/kg of water, depending on hydration status.
• Normal plasma osmolality is approximately 275–295 mOsm/kg of water.
• The ratio of urine osmolality to plasma osmolality is commonly greater than 1 and may reach 3–4 or higher when urine is highly concentrated.
• Assessment of urine osmolality helps evaluate the kidney’s ability to concentrate and dilute urine.

ADH Test

• The antidiuretic hormone test evaluates the renal response to antidiuretic hormone.
• Antidiuretic hormone promotes water reabsorption in the distal nephron and collecting ducts.
• In disorders such as nephrogenic diabetes insipidus, renal tubules respond poorly to antidiuretic hormone, resulting in impaired urine concentration.
• Following administration of antidiuretic hormone, urine specific gravity and osmolality are measured.
• Normal kidneys produce concentrated urine, with osmolality often exceeding 800 mOsm/kg after adequate stimulation.

Dilution Test

• The dilution test assesses the ability of the kidneys to excrete excess water.
• After administration of a controlled water load, urine samples are collected at regular intervals.
• Healthy kidneys excrete most of the ingested water within a few hours.
• Urine becomes dilute, with a specific gravity approaching 1.003 and osmolality decreasing to approximately 50–100 mOsm/kg.
• Failure to dilute urine appropriately may indicate impaired tubular function or excessive antidiuretic hormone activity.

Osmolal Clearance or Free Water Clearance

• Osmolal clearance represents the volume of plasma cleared of osmotically active substances per unit time.
• It is calculated from urine osmolality, plasma osmolality, and urine flow rate.
• Free water clearance reflects the kidney’s ability to excrete or conserve water independently of solute excretion.
• Positive free water clearance indicates excretion of dilute urine, whereas negative values indicate water conservation and urine concentration.
• These measurements are useful in evaluating polyuria, disorders of water balance, diabetes insipidus, and renal tubular dysfunction.

Specific Tests

Tests for Urine Acidification

• Specific renal function tests evaluate tubular secretion, urine acidification, sodium handling, and structural abnormalities of the kidneys.
• Urine acidification tests assess the ability of the renal tubules to excrete hydrogen ions and maintain acid–base balance.
• An acid load, commonly administered as ammonium chloride, is used to stimulate urinary acidification.
• Urine samples are collected periodically to measure urine pH and ammonium excretion.
• Healthy kidneys can lower urine pH to approximately 5.3 or less after acid loading.
• Failure to acidify urine adequately suggests impaired distal tubular function, as seen in certain forms of renal tubular acidosis.

Tests for Renal Handling of Na+

• Tests of sodium handling evaluate the capacity of renal tubules to conserve or excrete sodium according to physiological needs.
• Following a controlled sodium load, urinary sodium excretion is measured.
• During a low-sodium diet, healthy kidneys markedly reduce sodium excretion to preserve body sodium stores.
• Persistent urinary sodium loss despite sodium restriction indicates defective tubular sodium reabsorption.
• Such abnormalities may occur in tubular disorders associated with excessive natriuresis.

PSP Test

• The phenol red excretion test was historically used to assess tubular secretory function.
• Phenol red is actively secreted by proximal tubular cells and its urinary excretion reflects tubular secretory capacity.
• Reduced excretion may indicate impaired tubular function.
• However, this test has largely been replaced by more accurate and standardized assessments of renal function in modern clinical practice.

Special Tests

• Imaging studies provide important structural information about the kidneys and urinary tract.
• Ultrasonography is commonly used to evaluate kidney size, obstruction, cysts, and other anatomical abnormalities.
• Computed tomography and magnetic resonance imaging provide detailed visualization of renal parenchyma, blood vessels, and surrounding structures.
• Contrast-based imaging studies may be useful in selected patients but require caution in those with impaired renal function.
• Renal biopsy involves obtaining a small tissue sample for microscopic examination.
• It is valuable for diagnosing glomerular diseases, interstitial disorders, unexplained renal dysfunction, and monitoring certain kidney diseases.
• These investigations complement biochemical tests and provide a comprehensive assessment of renal function and structure.

Renal Failure

• Renal failure is a reduction in kidney function that impairs the regulation of fluid, electrolyte, and metabolic balance.
• It may develop rapidly as acute kidney injury or gradually as chronic kidney disease.

Acute Renal Failure

Definition and Causes

• Acute kidney injury is characterized by a sudden decline in renal function occurring over hours to days.
• It is often associated with decreased urine output, although urine volume may remain normal in some patients.
• Causes are classified as prerenal, intrinsic renal, or postrenal.
• Severe volume depletion and shock are common prerenal causes.
• Acute tubular necrosis is the most frequent intrinsic renal cause.
• It commonly results from ischemia, nephrotoxic drugs, chemicals, or severe infections.
• Early recognition improves the likelihood of recovery.

Table 82.3: Causes of renal failure.

Type of Renal Failure	Major Categories	Common Causes
Acute Kidney Injury	Prerenal	Heart failure, severe blood loss, dehydration, renal hypoperfusion, renal artery stenosis
	Intrinsic Renal	Acute tubular necrosis, glomerular diseases, tubulointerstitial disorders, sepsis, nephrotoxins
	Postrenal	Urinary tract obstruction due to stones, tumors, or prostatic enlargement
Chronic Kidney Disease	Progressive Renal Damage	Diabetes mellitus, hypertension, glomerular diseases, chronic interstitial nephropathies, renovascular disease, inherited disorders, systemic inflammatory diseases

Features

• Acute kidney injury commonly presents with oliguria, defined as urine output less than 400–500 mL per day in adults.
• Retention of nitrogenous waste products leads to uremia and systemic manifestations.
• Hyperkalemia is a frequent and potentially life-threatening complication because impaired renal excretion causes potassium accumulation.
• Hyponatremia may occur due to water retention, and metabolic acidosis develops from reduced acid excretion.
• Hypocalcemia can occur because diseased kidneys produce less active vitamin D, reducing intestinal calcium absorption.
• Uremic manifestations include anorexia, nausea, vomiting, lethargy, confusion, muscle twitching, hiccups, seizures, and coma in severe cases.
• Fluid overload may cause pulmonary edema, resulting in breathlessness and impaired gas exchange.
• Anemia may develop due to reduced erythropoietin production and associated illness.
• Bleeding tendencies can occur because of platelet dysfunction and abnormalities of hemostasis.
• Gastrointestinal bleeding may be seen in severe uremia.

Treatment

• Treatment begins with prompt assessment of airway, breathing, circulation, and underlying cause.
• Hyperkalemia requires urgent management to prevent cardiac arrhythmias.
• Intravenous calcium salts stabilize the cardiac membrane, while insulin with glucose promotes intracellular potassium uptake.
• Sodium bicarbonate may be used when significant metabolic acidosis is present.
• Circulating blood volume should be restored in patients with hypovolemia using appropriate intravenous fluids or blood products.
• Fluid balance, electrolyte concentrations, acid–base status, and urine output must be monitored regularly.
• Treatment of the underlying cause is essential, including management of acute tubular injury, infections, or urinary tract obstruction.
• Early control of infection reduces complications and improves outcomes.
• Renal replacement therapy, including hemodialysis, hemofiltration, hemodiafiltration, or peritoneal dialysis, is indicated for severe uremia, refractory hyperkalemia, significant metabolic acidosis, or fluid overload unresponsive to medical treatment.

Chronic Renal Failure (CRF)

Definition

• Chronic kidney disease is a progressive and usually irreversible decline in renal function that develops over months to years.
• It results in gradual loss of the excretory, endocrine, and metabolic functions of the kidneys.
• Advanced disease associated with severe loss of kidney function and dependence on renal replacement therapy is termed end-stage kidney disease.

Etiopathogenesis

• The most common causes worldwide are diabetes mellitus and hypertension.
• Other causes include glomerular diseases, chronic tubulointerstitial disorders, inherited kidney diseases, and renovascular disorders.
• Progressive nephron loss leads to impaired regulation of water, electrolytes, and acid–base balance.
• Accumulation of metabolic waste products and uremic toxins contributes to the clinical manifestations of uremia.

Features

• Early disease may be detected by elevated serum creatinine, increased blood urea, proteinuria, or reduced estimated glomerular filtration rate.
• Many patients remain asymptomatic until kidney function declines substantially.
• Nocturia is an early symptom caused by impaired urinary concentrating ability.
• Fatigue, reduced exercise tolerance, and breathlessness are common due to anemia and metabolic disturbances.
• Patients with advanced disease may develop anorexia, nausea, vomiting, pruritus, hiccups, muscle twitching, drowsiness, and cognitive impairment.
• Fluid overload may cause peripheral edema and cardiovascular complications.
• Persistent metabolic acidosis may produce deep, rapid breathing and contribute to muscle wasting and bone disease.
• Anemia commonly occurs because of reduced erythropoietin production by the kidneys.
• Disturbances of calcium, phosphate, and vitamin D metabolism may lead to chronic kidney disease–mineral and bone disorder.

Treatment

• Management focuses on identifying and treating the underlying cause and slowing disease progression.
• Strict control of diabetes and blood pressure is essential.
• Fluid, electrolyte, and acid–base abnormalities should be corrected.
• Anemia and mineral-bone disorders require appropriate treatment.
• Renal replacement therapy, including dialysis or kidney transplantation, is indicated in advanced disease.