This document defines chronic kidney disease (CKD) and describes its stages based on glomerular filtration rate (GFR). The main causes of CKD are then discussed, including hypertension, diabetes, glomerulonephritis, and urinary tract obstructions. For each cause, the document explains the pathophysiological changes that occur at the glomerular and tubular levels to reduce kidney function over time. Symptoms and complications of decreased GFR are also outlined. Finally, the document reviews treatment approaches for CKD including tight blood pressure and glucose control, avoidance of nephrotoxins, diet modification, and management of complications.

1. CHRONIC KIDNEY DISEASE (CKD)
MED-INTERN: MANDAL, AJAY KUMAR
BICOL MEDICAL CENTER
DEFINITION:
Progressive loss of renal function over time; based on a gradual decline in the GFR and creatinine clearance. The
diagnosis of CKD requires the following:
1. Decline of kidney function for 3 months or more AND
2. Evidence of kidney damage (e.g., albuminuria or abnormal biopsy) OR
GFR <60 mL/min/1.73 m2
Each patient is classified into one of the following 5 stages of CKD because management and prognosis varies according
to the progression of damage.
Stage 1 Kidney damage with normal or increased GFR (>90 mL/min/1.73 m2)
Stage 2 Mild reduction in GFR (60-89 mL/min/1.73 m2)
Stage 3 Moderate reduction in GFR (30-59 mL/min/1.73 m2)
Stage 4 Severe reduction in GFR (15-29 mL/min/1.73 m2)
Stage 5 Kidney failure (GFR <15 mL/min/1.73 m2 or dialysis)
ETIOLOGY AND PATHOGENESIS:
Many causes of CKD exist, however, this chapter will focus on the most prevalent causes including hypertension,
diabetes, glomerulonephritis and urinary tract obstructions.

2. HYPERTENSION
 Glomerular and vascular changes:
o Elevated systemic blood pressures cause a hypertrophic response leading to intimal thickening
of the large and the small vasculature.
o The mechanisms are compensatory at first, but later lead to glomerular damage
 Global sclerosis – ischemic injury to the nephrons causes death
 Focal segmental sclerosis – glomerular enlargement for compensation of the loss of
nephrons in other areas of the kidney.
 Interstitial nephritis:
o The vascular and glomerular disease lead to tubular atrophy and an intense chronic interstitial
nephritis
 The intense chronic interstitial nephritis is thought be secondary to immunologic
processes against ischemia-mediated antigen changes on the tubular epithelial cell
surface.
 Chronically these changes lead to tubular and glomerular loss causing nephrons loss.
o With the death of some nephrons, less are available to maintain the GFR.
o Gradual decline in the GFR is noticed as the nephrons continue to die.
DIABETES –DIABETIC NEPHROPATHY:
 Majority of the literature in the area is applied to the diabetic nephropathy patients based on data
hypothesized from the findings in animal models.
 Chronic hyperglycemia thought to be the primary cause of diabetic nephropathy.
o Unlike other tissues of the body, transmembrane glucose transporters (GLUT) receptors do not
facilitate intracellular glucose transport in the kidneys.
o This effect is mediated via a number of mechanisms including:
(i) glomerular hyperfiltration,
(ii) direct effects of hyperglycemia, and
(iii) advanced glycosylation end products (AGE), and
(iv) cytokine secretion.
 Glomerular hyperfiltration:
o Glomerular hyperfiltration is mediated mainly via dilatation the afferent arteriole leading to a
rise in the GFR and the renal blood flow.
o This dilatation of the afferent arteriole is mediated by a number of mechanisms in diabetic
nephropathy:
 Hyperglycemia and high insulin-like growth factor-1 (IGF-1) concentrations
(observed in diabetic patients) – both are hypothesized to cause a rise in the GFR
increasing renal flow
 Hyperfiltration of glucose leads to augmented sodium-glucose transport in the
proximal convoluted tubule causing enhanced sodium transport
 Cause expansion of blood volume which leads to a rise in GFR
 The rise in proximal reabsorption also leads to a reduced distal fluid
delivery which activates the tubule-glomerular feedback with the
renin-angiotensin system which works to raise the GFR as well.
 Hyperglycemia and AGE:
o Hyperglycemia and AGE directly induce mesangial matrix production, cellular expansion and
apoptosis.

3. o The two have also been shown to increase basement membrane permeability to albumin.
 Cytokines:
o Elevations in vascular endothelial growth factor (VEGF), transforming growth factor beta (TFG-
β), and profibrotic proteins increase damage to the nephrons at different levels; specific
mechanisms are unclear.

4. GLOMERULONEPHRITIS
 Glomerular injury takes place via inflammatory as well as non-inflammatory mechanisms in different types
of glomerulonephritides.
 Non-inflammatory injury:
o Common examples of this include the podocytopathies; minimal change nephrotic
syndrome/focal segmental glomerulosclerosis (MCNS/FSGS) and membranous
nephropathy(MN)
 A dramatic rise in the glomerular permeability without any evidence of
inflammation on light microscopy.
 Several cytokines such as IL-13 and members of the complement system C3, C5b-9
lead to glomerular basement membrane thickening, as well as podocyte damage,
apoptosis, detachment and excretion in the urine. This induces glomerular
sclerosis.
 Inflammatory injury:
o Common examples include post-streptococcal
glomerulonephritis (GN), membranoproliferative GN, Henoch-Schönlein purpura (HSP),
systemic lupus erythematosus (SLE), some forms of rapidly progressive
glomerulonephritis (RPGN), IgA nephropathy, hemolytic uremic syndrome (HUS) and
various vasculitides.
o This inflammatory injury has been found to be mediated by a number of mechanisms:
 Some members of the complement system such as C5a have been implicated in
inflammatory injury via inducing antibody deposition and activation and
recruitment of polymorphonuclear cells (PMNs); neutrophil,
macrophage/monocyte, platelets and T-cells.
 These cells produce oxidants and proteases that cause fibrin deposition, capillary
wall damage and produce proteinuria.
 Unlike podocyte targeting in non-inflammatory injury, disorders in which
glomerular endothelial and mesangial cells are principally involved exhibit a more
dramatic response to immune injury. This response is usually characterized by cell
proliferation and phenotype change, as well as readily visible structural changes in
the renal biopsy.
Post-Renal CKD: See Urology.
PATHOPHYSIOLOGY
 Patients with stages 1-3 ([GFR] >30 mL/min) of CKD are generally asymptomatic; water/electrolyte
imbalances or endocrine/metabolic derangements are not clinically evident.
 These disturbances manifest clinically in CKD stages 4-5 (GFR < 30 mL/min).
Sign/lab finding Symptoms Mechanism
Generalized edema Swelling Water retention due to a loss of GFR leading to sodium and fluid
retention. Fluid moves into the extravascular space, due to
increased hydrostatic pressure, causing pitting edema in the lower
extremity (fluid movement could also be due to hypoalbuminemia,
in some diseases, leading to a low oncotic pressure).

5. Pulmonary crackles Shortness of breath Fluid accumulation causes pulmonary edema and loss of air space
causing ventilation-perfusion mismatch. This leaves less area for
oxygen diffusion form the blood vessels.
Anemia Fatigue, reduced
exercise capacity,
and pallor
Erythropoietin (EPO), the major erythropoiesis stimulator, is
released from the kidneys; with renal failure, there is loss of EPO
release.
Weight loss Loss of lean body
mass
Protein-energy malnutrition due to metabolic acidosis. Loss of
kidney function results in impaired H+ secretion from the body.
Hyperkalemia Malaise, palpitations Inability of the kidneys to secrete potassium in the urine leads to
life threatening arrhythmias.
Mechanisms of renal osteodystrophy
Hyperphosphatemia Damaged kidneys fail to excrete phosphate.
Also secondary to high parathyroid hormone levels.
Hypocalcemia Thought to be secondary to low Vitamin D3 levels. In early stages of
CKD, low levels of calcitriol are due to hyperphosphatemia
(negative feedback). In the later stages of CKD, low levels are
hypothesized to be due to decreased synthesis of 1α-hydroxylase
(enzyme that converts calcifediol to calcitriol in the kidneys).
Secondary and
tertiary
hyperparathyroidism
To compensate for the low calcium due to low Vitamin D levels, the
parathyroid glands increase the parathyroid hormone secretion.
This leads to a high bone turnover, always attempting to normalize
the low calcium levels in the blood. Over time, this becomes
maladaptive leading to extraosseous calcification, and parathyroid
hyperplasia develops (tertiary hyperparathyroidism).
Complications of uremia
Urea and other toxins accumulate in the blood and cause life threatening issues.
Ecchymosis, GI
bleeding
Increased tendency
to bleed and
ecchymosis
Uremia-induced platelet dysfunction
Pericardial friction
rub
Chest pain, malaise Uremic pericarditis
Headaches,
confusion, coma
Uremic encephalopathy; adverse effects of urea on the CNS.
Mechanisms unclear.

6. TREATMENT:
 Cardiovascular disease (CVD)is the leading cause of death in patients with CKD.
o Reducing risk factors for development of CVD is beneficial.
 E.g. treatment of hyperlipidemia, lifestyle and dietary changes
 Tight blood pressure control:
o Reducing damage due to the end organ effects of hypertension on the kidney as well as the
heart.
o Angiotensin-converting enzyme inhibitors (ACEI) and angiotensin II receptor
blockers(ARBs) block the effects of angiotensin II on (i) sodium and fluid retention, (ii)
vasoconstriction, (iii) stimulating ADH release, (iv) stimulating aldosterone release, and (v)
inducing a sympathetic response.
 ACEIs and ARBs also slow down progression of proteinuria in patients with diabetic
CKD.
 Diabetes management:
o Tight glucose management slows the progression of vascular and heart disease.
 Avoidance of IV contrast, NSAIDs, and nephrotoxic drugs:
o These agents can potentially induce an acute kidney injury (AKI) on the underlying kidney
disease and therefore exacerbate the baseline CKD.
 Diet:
o Mixed evidence exists whether dietary protein restriction is beneficial in slowing disease
progression.
o Proteins affect the renal hemodynamics, raising the GFR, in hypothesized 2 ways.
 Hormonal effects – proteins cause secretion of glucagon, IGF-1 and kinins, all of
which have been shown to raise the GFR.
 Tubuloglomerular effects – high amino acid (AA) filtration leads to increased AA and
hence the sodium uptake in the proximal convoluted tubule. A decreased sodium
delivery to the distal convoluted tubule leads to the rennin-angiotensin system

7. activation via the macula densa and these work to raise the GFR (mechanisms
above)
o Controlling hyperphosphatemia: Protein restriction also limits phosphorus consumption.
Hyperphosphatemia plays a major role in the progression of renal osteodystrophy. Phosphate
binders are used to reduce phosphate absorption through the GI tract.