Kidney Disease

Nutrition & Chronic Kidney Disease


Learning Objectives

  • Describe normal physiological functioning of the kidneys, including pathophysiology and impact on kidney function.

  • Discuss the etiologies and risk factors for Chronic Kidney Disease (CKD) as well as medical treatment for end-stage renal disease.

  • Explain medical nutrition therapy for CKD, covering assessment, intervention, and recommendations.

  • Review videos on Acute Kidney Injury and Nephrolithiasis.


Fascinating Facts about the Kidney

  1. An adult's kidney weighs about 142 grams (5 ounces) and is roughly the size of a fist or a cellphone.

  2. Kidneys have a higher blood flow compared to both the brain and liver.

  3. There are approximately 2 million nephrons in healthy kidneys which, if stretched out, measure about 8 km (5 miles) long.

  4. Dehydration is a common cause of kidney stones. Drink plenty of water as the largest recorded kidney stone was 1.1 kilograms (2.5 lbs).

  5. Kidneys filter approximately 1,514 liters (400 gallons) of blood daily.


Types of Kidney Stones

  • Calcium Stones: Most common (about 80% of stones). Often calcium oxalate, but can be calcium phosphate. Linked to high calcium excretion, high oxalate intake (e.g., from spinach, rhubarb), or certain bowel diseases.

  • Uric Acid Stones: Occur in people with high uric acid levels (e.g., gout) or those who don't drink enough fluids. These stones are not visible on standard X-rays.

  • Struvite Stones: Less common, often larger, and typically result from urinary tract infections (UTIs) caused by certain bacteria that produce ammonia.

  • Cystine Stones: Rare, caused by a hereditary disorder (cystinuria) that leads to excessive excretion of the amino acid cystine.


The Nephron - Functional Unit of the Kidney

  • Function: Filters blood to remove waste and excess water, reabsorbing necessary substances before excretion as urine.

  • **Components:

    • Glomerulus:** Primary filtering unit that separates waste products and excess fluid from blood.

    • Loop of Henle: A U-shaped portion of the nephron responsible for the recovery of water and sodium chloride from urine. Impaired function here can lead to issues with fluid and electrolyte balance, directly impacting nutritional status and the need for dietary adjustments.

  • Loop Diuretics: Such as furosemide, decrease the reabsorption of sodium (Na⁺) and chloride (Cl⁻) ions in the thick ascending limb of the loop of Henle.


Physiological Functions of the Kidneys

  • Maintenance of homeostasis through:

    • Fluid Control: Adjusting absorption of water.

    • pH Control: Regulating hydrogen and bicarbonate ions.

    • Electrolyte Balance: Regulating sodium and potassium levels.

    • Blood Pressure Control: Managing blood volume through the reabsorption of sodium and water.

  • Excretion of: Metabolic waste products and foreign substances.

  • Production of: Enzymes and hormones.


A WET BED - Functions of the Kidneys in Acronym Form

  • A: Acid-base balance.

  • W: Water balance.

  • E: Electrolyte balance.

  • T: Toxin removal.

  • B: Blood pressure control.

  • E: Erythropoietin production (important for red blood cell production).

  • D: Activation of vitamin D.


Markers of Renal Function

  • Glomerular Filtration Rate (GFR):

    • Standard marker for kidney function, calculated based on blood creatinine, age, body size, gender. Often referred to as estimated GFR (eGFR) in clinical practice. The GFR value is central to staging CKD.

    • Average filtration = 135−180135-180 L/day.

    • Normal GFR: >90>90 mL/min/1.731.73 m² BSA.

  • Blood Urea Nitrogen (BUN):

    • Measures urea nitrogen in the blood which increases with decreased kidney function.

  • Creatinine:

    • Indicates kidney performance by measuring creatinine levels in blood. Men generally have higher levels.

Chronic Kidney Disease (CKD)

  • Defined as an irreversible disease affecting glomerular, tubular, and endocrine renal function.

  • Characterized by a progressive loss of kidney function for >3>3 months.

  • Effects: Inability to filter waste and fluids leading to toxin buildup.

  • Kidney failure occurs when **1/41/4 to **2/32/3 of kidney function is lost, regardless of the underlying cause.

  • The kidney adapts to decreases in GFR.


Causes of Chronic Kidney Disease

  • Other causes include:

    • Polycystic Kidney Disease

    • Interstitial tubular nephritis

    • Congenital kidney issues

    • Drug-induced causes.


Risk Factors for Kidney Disease

  • CKD has a higher mortality rate than most forms of cancer.

  • Cardiovascular disease (CVD) is the leading cause of death among patients with CKD.


CKD Tests & Diagnosis

  • Early kidney disease is often asymptomatic. Testing is key for detection, especially for those with:

    • Diabetes

    • High blood pressure

    • Heart disease

    • Family history of kidney disease.

  • Regular check-ups are recommended for high-risk individuals.

Laboratory Evaluation of Kidney Function

  • GFR results: Show filtration levels; a healthy kidney does not allow albumin to pass into urine.

  • Clearance Tests: Measures substances cleared from plasma.

    • Normal serum creatinine:

      • Female: 50−9050-90 µmol/L

      • Male: 70−12070-120 µmol/L

  • Proteinuria: Indicates kidney damage with a higher Albumin to Creatinine Ratio (ACR) signaling increased CKD risk.


Stages of Chronic Kidney Disease

  • Stage 0: Increased risk (GFR ≥60\ge60 with CKD risk factors).

  • Stage 1: Kidney damage with normal/increased GFR (≥90\ge90) - Diagnosis and treatment needed.

  • Stage 2: Mild reduction (60−8960-89) - Evaluation for progression.

  • Stage 3 (a and b): Moderate reduction (45−5945-59 or 30−4430-44) - Treat complications and slow progression.

  • Stage 4: Severe reduction (15−2915-29) - Prep for kidney replacement therapy.

  • Stage 5: Kidney failure (<15<15 or dialysis) - Replacement therapy is urgent.


Signs & Symptoms of Renal Disease

  • Patients with stages 1-3 are generally asymptomatic; symptoms often appear in stages 4-5.

  • Manifestations include:

    • Generalized edema

    • Pulmonary crackles (shortness of breath)

    • Anemia

    • Weight loss

    • Fatigue and reduced exercise capacity.


Pathophysiology of CKD Symptoms

  • Generalized Edema: Caused by fluid retention due to loss of GFR and sodium retention, leads to pitting edema.

  • Pulmonary Symptoms: Fluid accumulation leads to pulmonary edema and ventilation-perfusion mismatch.

  • Anemia: Loss of Erythropoietin (EPO) production due to renal failure, leading to reduced red blood cell production.

  • Weight Loss/Fatigue: Related to protein-energy malnutrition and metabolic acidosis.

  • Hyperkalemia: Renal failure leads to potassium retention, risking life-threatening arrhythmias.


Uremia in CKD

  • Uremia: Accumulation of waste products, causing:

    • GI symptoms: Nausea, vomiting.

    • Neurological symptoms: Confusion.

    • Cardiovascular: Hypertension and pericarditis.

    • Dermatological: Pruritus.

  • Uremia is particularly severe in late stage 4 and stage 5 CKD, necessitating dialysis.


Renal Osteodystrophy (Mineral and Bone Disease)

  • Mechanisms:

    • Hyperphosphatemia due to poor phosphate excretion from damaged kidneys, potentially leading to elevated parathyroid hormone levels.

    • Hypocalcemia due to low Vitamin D levels, leading to increased parathyroid hormone and bone turnover.

    • High bone turnover can cause maladaptation over time leading to extraosseous calcification and parathyroid hyperplasia.


Complications of CKD

  • Kidney Functions Affected:

    • Sodium balance (retention)

    • Potassium excretion (hyperkalemia)

    • Acid excretion (metabolic acidosis)

    • Calcium/phosphate balance (hypocalcemia, hyperphosphatemia)

    • Erythropoiesis (anemia).


Treatment & Management of CKD

  • Goals of Treatment:

    • Treat underlying conditions (hypertension, diabetes)

    • Adopt a healthy lifestyle (diet, exercise)

    • Use of medications (SGLT-2, GLP-1, ACE Inhibitors, ARBs).

    • Cardiovascular disease risk management.

    • Address complications and symptoms.


Renal Replacement Therapies

  • Peritoneal Dialysis (PD):

    • Utilizes peritoneal membrane as a filter; involves the instillation of dialysis fluid into the peritoneal cavity.

    • Risks: Infection, home supply requirements.

  • Hemodialysis (HD):

    • External artificial filter cleans blood outside the body, requires access via needles.

    • Risks: Clots, infections, and complications like “steal syndrome.”

    • Modes include in-center, home, and nocturnal dialysis.


Kidney Transplant

  • Can be from deceased donors or living donors; offers better outcomes compared to dialysis.

  • Living donor kidneys generally last longer than deceased donor kidneys.


Nutritional Therapy in CKD

  • Key focus areas include:

    • Maintaining nutritional status

    • Preventing protein energy malnutrition

    • Slowing disease progression and managing complications.


Goals of the Renal Diet

  • Minimize waste products and fluid build-up.

  • Consider individual factors like stage, modality of renal replacement therapy, labs, lifestyle, and medications.


Fluid Management

  • Fluid restrictions may not be necessary until late CKD stages or dialysis.

  • 11 L fluid intake = 11 Kg weight gain; excess fluid may cause edema and hypertension.


Phosphorus Management

  • Importance of managing phosphorus levels to prevent cardiovascular complications.

  • Use of phosphate binders to limit dietary absorption and manage serum phosphate levels.

Dietary Guidelines for CKD

  • Emphasis on low potassium, low sodium, low phosphorus diets, and adequate energy intake.

  • Monitor dietary intake of proteins based on CKD stage and dialysis needs.


Case Study and Practical Applications

  • When approaching a patient case for nutritional intervention in CKD, consider:

    • eGFR and CKD Stage: This is the primary determinant for protein recommendations and the urgency of interventions.

    • Weight Loss/Nutritional Status: Assess for protein-energy wasting (PEW) or unintentional weight loss, which would prioritize adequate energy and protein intake to prevent malnutrition.

    • Blood Work: Key labs include serum potassium, phosphorus, calcium, BUN, creatinine, albumin, and hemoglobin. These guide specific micronutrient adjustments and management of complications like hyperkalemia or hyperphosphatemia.

    • Micronutrient Impact: For example, in later stages, attention to vitamin D activation issues (due to impaired kidney function) and potential need for calcium/phosphate balance management (e.g., phosphate binders, activated vitamin D analogs).

    • Prioritization: Address life-threatening electrolyte imbalances (e.g., severe hyperkalemia) immediately. Support nutritional status, manage fluid and electrolyte balance, and then focus on slowing disease progression and improving quality of life. Tailor recommendations by balancing restriction necessities with pleasure and feasibility to ensure adherence.

Summary of Key Messages for CKD Management

  • Individualized care focusing on:

    • Protein Energy Wasting

    • Sodium/Fluid Management

    • Mineralo-calcific balance (Calcium, Phosphorus)

    • Potassium and Water-soluble vitamins

    • Managing co-morbidities such as diabetes and dyslipidemia.

Additional Resources

  • NIDDK: Comprehensive information on kidney health, tests, and treatments.