Sickle Cell Nephropathy

Slide 1 · Sickle Cell Nephropathy

Vascular, medullary, and glomerular injury in HbS-associated disease

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Explain why the renal medulla favors sickling of HbS-containing erythrocytes.

Link sickling to hematuria, hyposthenuria, papillary necrosis, and proteinuria.

Distinguish renal manifestations of sickle cell trait from sickle cell disease.

Relate renal morphology to functional impairment and clinical interpretation.

Slide 3 · A syndrome of renal structural and functional alterations

Sickle cell nephropathy

An umbrella term for renal alterations occurring in people with sickle cell disease or sickle cell trait.

Kidney injury is not confined to individuals with homozygous HbS.

Slide 4 · Two genotypic settings: Disease and trait

Sickle cell disease

Homozygous HbS description.

Most hemoglobin is HbS.

Systemic sickling and vascular injury are prominent.

Sickle cell trait

Heterozygous HbAS description.

HbA inhibits HbS polymerization.

Renal medullary stress can still induce sickling.

Slide 5 · Renal involvement does not require generalized sickling

HbAS erythrocyte

Renal medullary hypoxia and hypertonicity

Local HbS polymerization

Renal manifestations

A locally stressful environment can unmask risk in sickle cell trait.

Slide 6 · A mechanism-to-lesion framework

Red cell

HbS polymerization and dehydration

Medullary vessels

Sickling under hypertonic, hypoxic conditions

Kidney

Concentrating defect, bleeding, papillary injury

Glomerulus

Proteinuria with possible sclerosis

Slide 7 · Renal cortex, medulla, and papillary tip

Cortex

Medulla

Papillary tip

Schematic—not a histologic section

Glomeruli lie in the cortex.

The medulla supports urine concentration.

The papillary tip is a recognized site of necrotic injury.

Slide 8 · Why the renal medulla is uniquely vulnerable

Low oxygen tension

Promotes HbS deoxygenation

Hypertonicity

Draws water from erythrocytes

Microcirculatory transit

Allows time for sickling in vulnerable beds

Slide 9 · The molecular origin: β-globin missense mutation

β-globin missense mutation

Glutamate → valine substitution

Abnormal hemoglobin S

Deoxygenation-dependent polymerization

A single amino-acid replacement changes the physical behavior of hemoglobin.

Slide 10 · Deoxygenation converts HbS into polymers

Oxygenated

Deoxygenated HbS

Deoxygenation

The relevant event is HbS polymer assembly—not an intrinsic inability to bind oxygen.

Original schematic

Slide 11 · Polymer formation changes red-cell mechanics

Deoxygenated HbS

Long intracellular polymers

Cell distortion and rigidity

Impaired microvascular transit

Vaso-occlusion is favored when polymerization develops during capillary passage.

Slide 12 · Sickling begins as a reversible deformation

Earlier episodes

Polymer formation after deoxygenation.

Shape distortion can reverse on reoxygenation.

Membrane damage may accumulate with repeated cycles.

Repeated episodes

Cells become dehydrated and rigid.

Some red cells become irreversibly sickled.

Mechanical fragility and removal increase.

Slide 13 · HbA limits polymerization in sickle cell trait

HbAS mixture

HbA interferes with HbS assembly

Lower usual sickling tendency

Severe local hypoxia can overcome protection

Slide 14 · HbF also counteracts HbS polymerization

HbS

Polymerizes when deoxygenated

HbA

Interferes with HbS polymerization

HbF

Inhibits HbS polymerization more strongly than HbA

Slide 15 · Intracellular HbS concentration is a key variable

Water leaves red cell

Cell volume decreases

HbS concentration rises

Polymer formation becomes more likely

Concentrating HbS within the erythrocyte accelerates sickling.

Slide 16 · Hypertonicity dehydrates medullary erythrocytes

Hypertonic medullary milieu

Water efflux from erythrocyte

Higher intracellular HbS

Accelerated sickling

This is the mechanism highlighted for both disease and trait.

Slide 17 · Low oxygen tension promotes HbS assembly

Local hypoxia

More deoxygenated HbS

Polymer accumulation

Erythrocyte distortion

Oxygen availability directly modulates the fraction of HbS that can polymerize.

Slide 18 · Intracellular acidity amplifies sickling

Lower intracellular pH

Reduced hemoglobin oxygen affinity

Higher deoxy-HbS fraction

Greater sickling tendency

General sickle cell pathogenesis; Not quantified for medullary renal injury here.

Slide 19 · Transit time matters in microvascular beds

Rapid transit

Limited time for substantial polymerization.

Less chance of intravascular cell distortion.

Illustrates the role of exposure duration.

Prolonged transit

Deoxygenated HbS persists longer.

Sickling becomes more probable.

Stasis may intensify vascular obstruction.

Slide 20 · Repeated sickling damages the red-cell membrane

HbS fibers deform membrane

Altered ion handling

K⁺ and H₂O loss

Dense, rigid erythrocyte

Membrane injury links repeated sickling to increased cellular dehydration.

Slide 21 · Inflammation can enhance sickle-cell adhesion

Inflammatory mediators

Endothelial adhesion signals

Erythrocyte retention

Stasis and hypoxia

The broader vasculopathy helps explain why local microvascular conditions matter.

Slide 22 · Hemolysis may decrease bioavailable nitric oxide

Intravascular hemolysis

Free hemoglobin

Nitric oxide scavenging

Higher vascular tone

This as a possible contributor to vaso-occlusion, not its sole cause.

Slide 23 · Sickling and hypoxia can reinforce one another

Sickling

Vascular obstruction

Local hypoxia

Further sickling

Reinforcing cycle (schematic)

Slide 24 · A renal medullary injury cascade

Hypertonic + hypoxic medulla

Erythrocyte dehydration

HbS polymerization

Local microvascular injury

Medullary dysfunction

Mechanism integrates the renal and hematologic Robbins sections.

Slide 25 · Why heterozygous HbAS is not completely protected

Systemic circulation

HbA interferes with polymerization.

Trait is largely asymptomatic in everyday conditions.

Short transit often limits HbS assembly.

Renal medulla

Low oxygen and hypertonicity coexist.

Erythrocytes become locally dehydrated.

Renal findings can occur even in trait.

Slide 26 · Clinical renal findings form two major clusters

Medullary–papillary

Hematuria · hyposthenuria · papillary necrosis

Glomerular

Proteinuria · glomerular sclerosis · occasional nephrotic syndrome

Slide 27 · Hematuria is a common renal manifestation

Hematuria

One of the two most common abnormalities grouped under sickle cell nephropathy.

Occurs in the context of HbS-associated renal injury; Other causes are not excluded.

Slide 28 · Hematuria indicates urinary red-cell loss

Clinical signal

Blood or erythrocytes detected in urine

Pathologic context

Medullary and papillary vulnerability in HbS states

Interpretation

Hematuria alone does not identify a specific renal lesion

Slide 29 · Hyposthenuria is impaired urine concentration

Hyposthenuria

A reduction in the kidney’s ability to concentrate urine.

It, alongside hematuria, as a common renal abnormality.

Slide 30 · Medullary injury undermines concentrating function

Medullary sickling

Medullary microvascular damage

Reduced concentrating ability

Hyposthenuria

The renal concentrating apparatus is vulnerable to ischemic injury.

Slide 31 · Hyposthenuria can aggravate dehydration risk

Medullary damage

Hyposthenuria

Greater dehydration propensity

More sickling risk

Reinforcing cycle (schematic)

Slide 32 · Distinguish solute concentration from urine volume

Hyposthenuria

Primary concept: Impaired urine concentration.

A renal functional abnormality.

Described explicitly in sickle cell disease and trait.

Dehydration risk

A clinical consequence of poor concentrating ability.

May worsen the milieu favoring sickling.

Do not infer a measured urine output from the term alone.

Slide 33 · Papillary necrosis is a focal ischemic lesion

Patchy papillary necrosis

May occur in either homozygous sickle cell disease or heterozygous sickle cell trait.

The renal papilla is the anatomic focus; An entire cortical infarct is a different lesion.

Slide 34 · Localize papillary necrosis anatomically

Cortex

Medulla

Papillary tip

Injury focus

Schematic—not a histologic section

Injury centers on papillary / pyramidal tissue.

Patchy papillary necrosis.

A schematic is used here; No genuine photomicrograph supplied.

Slide 35 · Gross pattern of papillary necrosis

Site

Tips or distal parts of renal pyramids

Gross appearance

Gray-white to yellow necrotic areas

Extent

One or multiple papillae; Unilateral or bilateral

Slide 36 · Microscopic correlate: Ischemic coagulative necrosis

Papillary ischemic injury

Coagulative tissue necrosis

Tubular outlines may persist

Limited leukocytes at injury margins

General papillary necrosis morphology from the renal chapter; Schematic relationship only.

Slide 37 · Papillary injury can vary in distribution

Patchy involvement

Necrosis is not necessarily uniform.

Individual papillae may be affected.

Robbins specifically uses “patchy.”

More extensive injury

Several papillary regions may be involved.

Associated ischemic damage can be more widespread.

Do not assume a fixed extent in every case.

Slide 38 · Cortical scarring may accompany papillary necrosis

Renal sickling injury

Patchy papillary necrosis

Sometimes associated with cortical scarring

Association is stated in the source; A single causal route is not established.

Slide 39 · Papillary necrosis has multiple clinical contexts

Context

Robbins relationship

Sickle cell disease / trait

Papillary necrosis can occur.

Diabetes mellitus

Recognized associated condition.

Urinary tract obstruction

Recognized associated condition.

Acute pyelonephritis

May have superimposed papillary necrosis.

Slide 40 · Proteinuria is frequent in sickle cell disease

About 30%

Proteinuria in approximately 30% of patients with sickle cell disease.

This is a textbook estimate; It is not presented as an updated population-specific prevalence.

Slide 41 · Proteinuria is usually mild to moderate

Sickle cell disease

Proteinuria develops

Usually mild or moderate

Occasionally nephrotic syndrome

Protein loss has a broad clinical severity spectrum.

Slide 42 · Sclerosing glomerular lesions explain severe protein loss

Glomerular sclerosing lesions

Glomerular filtration barrier dysfunction

Proteinuria

Occasional nephrotic syndrome

Overt nephrotic syndrome with sclerosing glomerular lesions.

Slide 43 · Nephrotic syndrome is not the typical presentation

Usual proteinuric finding

Proteinuria may be present.

Usually mild to moderate.

Does not by itself establish nephrotic syndrome.

Occasional severe presentation

Overt nephrotic syndrome can arise.

Associated with glomerular sclerosis.

A distinct manifestation within a broad spectrum.

Slide 44 · Glomerular injury and medullary injury are distinct

Medullary / papillary

Hypertonic and hypoxic milieu.

Hyposthenuria and hematuria.

Patchy papillary necrosis.

Glomerular

Proteinuria is a major signal.

Sclerosing lesions may be present.

Occasional nephrotic syndrome.

Slide 45 · Link renal structure to the clinical phenotype

Site / lesion

Functional or clinical correlate

Medullary concentrating region

Hyposthenuria

Medullary / papillary injury

Hematuria

Papillary tissue necrosis

Patchy papillary necrosis

Sclerosing glomerular lesions

Proteinuria; Sometimes nephrotic syndrome

Slide 46 · The disease–trait comparison is lesion-specific

Manifestation

Sickle cell disease

Sickle cell trait

Renal involvement

Possible

Possible

Hyposthenuria

Highlighted in renal passage

Explained by local medullary sickling

Papillary necrosis

Explicitly described

Explicitly described

Proteinuria ~30%

Estimate applies here

No frequency stated in source

Slide 47 · Do not conflate papillary necrosis and renal infarction

Papillary necrosis

Localized in renal papillae / pyramids.

Patchy lesions occur with HbS states.

Ischemic coagulative necrosis is possible.

Renal infarction

Often embolic in the renal chapter.

Classically wedge-shaped cortical lesions.

May heal as depressed cortical scars.

Slide 48 · Kidney injury can progress through nephron loss

Glomerular, tubular, or vascular injury

Loss of functional nephrons

Adaptive hyperfiltration

Further nephron injury

General CKD mechanism from the adjacent Robbins section; Not a measured trajectory in this lecture.

Slide 49 · Chronic kidney disease has convergent morphology

Glomeruli

Glomerulosclerosis

Tubules

Tubular atrophy

Interstitium

Interstitial fibrosis

Vessels

Arteriosclerosis

Slide 50 · Avoid over-attributing urinary abnormalities to HbS

Hematuria

A clinical sign, not a specific morphologic diagnosis

Concentrating defect

Implies medullary functional impairment

Proteinuria

Warrants consideration of glomerular injury

Renal scarring

Requires interpretation in the full pathologic context

Slide 51 · Clinical vignette: Hematuria in HbAS trait

Constructed teaching vignette

An individual known to have sickle cell trait presents with hematuria. There is no established systemic vaso-occlusive syndrome in the vignette.

Can HbAS be relevant to the renal presentation?

Yes. The medullary milieu can promote local sickling even in trait.

Hematuria remains nonspecific; Other causes must still be considered.

Slide 52 · Clinical vignette: Interpretation of hyposthenuria

Constructed teaching vignette

A patient with sickle cell disease has a documented inability to concentrate urine appropriately.

Which renal region is central to the textbook mechanism?

The hypoxic, hypertonic renal medulla.

The local tendency for HbS-containing erythrocytes to sickle.

Slide 53 · Clinical vignette: Proteinuria in sickle cell disease

Constructed teaching vignette

A patient with sickle cell disease has persistent proteinuria, now considerably more pronounced than previously documented.

Which lesion category is linked to the severe proteinuric phenotype?

Sclerosing glomerular lesions.

Overt nephrotic syndrome is possible but not the usual severity.

Slide 54 · Morphology challenge: Identify the compartment

Finding

Most relevant compartment

Poor urine concentration

Renal medulla

Patchy papillary necrosis

Renal papilla

Proteinuria with sclerosis

Glomerulus

Possible cortical scar

Cortex (associated finding)

Slide 55 · Mechanism challenge: Order the causal steps

Medullary hypertonicity

Red cell dehydration

Increased intracellular HbS

Accelerated sickling

Medullary injury

A mechanistic sequence supported directly by the renal text.

Slide 56 · Diagnostic reasoning: What the source does not establish

Hematuria alone does not establish papillary necrosis.

No biopsy-defined grading or staging system is provided for sickle cell nephropathy.

The approximately 30% proteinuria estimate applies to sickle cell disease in the source.

No source-specific testing thresholds or treatment algorithm is supplied.

Slide 57 · Integrated renal injury model

Triggering milieu

Medullary hypoxia and hypertonicity

Cell response

HbS polymerization and red-cell sickling

Regional damage

Concentrating defect and papillary necrosis

Glomerular phenotype

Proteinuria; Possible sclerosis and nephrotic syndrome

Slide 58 · Five clinicopathologic conclusions

Both sickle cell disease and trait may affect the kidney.

Medullary hypertonicity and hypoxia favor HbS sickling.

Hematuria and hyposthenuria are common renal abnormalities.

Papillary necrosis may be patchy and may coexist with cortical scarring.

Proteinuria is common in disease; Occasional nephrotic syndrome accompanies glomerular sclerosis.

Slide 59 · Source materials and scope

Robbins, Cotran & Kumar: Pathologic Basis of Disease, 11th edition (2026).

Chapter 20: The Kidney — Sickle Cell Nephropathy; renal papillary necrosis; chronic kidney disease; renal infarcts.

Chapter 14: Red Blood Cell and Bleeding Disorders — Sickle Cell Disease.

Original visual diagrams and constructed vignettes created for this lecture; no textbook micrographs reproduced.