RF, Etiology, Pathophys
List the risk factors of ATN. (300 pts)
Age: Age 65 or older.
Pre-existing Kidney Function: Underlying CKD or renal insufficiency.
Chronic Systemic Comorbidities: Diabetes, heart failure, liver disease, advanced malignancy, or atherosclerosis.
Hemodynamic and Procedural Instability: Hypotension, septic shock, surgical blood loss, blood clots, or severe transfusion reactions.
Endogenous Stressors: Rhabdomyolysis.
Formulate a differential diagnosis for ATN. (400 pts)
Prerenal azotemia - functional GFR drop from renal hypoperfusion (e.g., dehydration, heart failure); tubules remain intact.
Acute interstitial nephritis - inflammatory/allergic reaction in the renal interstitium, usually drug-induced (e.g., NSAIDs, antibiotics).
Acute glomerulonephritis - direct inflammatory damage to glomerular capillary loops instead of tubules.
Chronic kidney disease - progressive, permanent renal function loss over months to years.
Other drug-induced nephrotoxicities - tubular lumen obstruction via micro-crystal precipitation rather than direct cell wall necrosis.
What are the different types of cells detected in a urinalysis? (400pts)
Renal Tubular Epithelial Cells (RTECs): Shed from tubule linings due to acute damage and sloughing. Their presence is a hallmark of Acute Tubular Necrosis (ATN) and indicates active structural damage.
Red Blood Cells (RBCs): Normally absent. An abundance indicates glomerular injury or postrenal bleeding compromising the filtration barrier
White Blood Cells (WBCs/Leukocytes): Normally absent or minimal. An abundance (pyuria), particularly with WBC casts, indicates inflammation or infection like AIN or pyelonephritis.
Research other toxin-induced causes of ATN. (400 pts)
Medications: Antibiotics (vancomycin, colistin), antifungals (amphotericin B), NSAIDs, and chemotherapies (cisplatin).
Diagnostic Agents: Radiographic contrast dyes used in CT scans.
Poisons & Heavy Metals: Ethylene glycol (antifreeze), lead, and mercury.
Endogenous Toxins: Internal waste such as myoglobin (from rhabdomyolysis) or hemoglobin (from hemolysis).
What are the phases of ATN? (300 pts)
Initiation Phase: Triggered by initial ischemic or toxic insult (hours to days), showing sudden GFR drop and rising creatinine/BUN.
Extension Phase: Marked by ongoing hypoxia and outer medulla/corticomedullary junction inflammation.
Maintenance Phase: Lasts 1–3 weeks with impaired filtration, early repair, and oliguria.
Recovery Phase: Lasts up to 2 weeks; tubular proliferation normalizes GFR and blood flow, causing polyuria because the newly regenerated tubules cannot concentrate urine effectively yet
What are the OSE findings in ATN? (400 pts)
Chapman's Points for Kidney: 1 inch superior and lateral to the umbilicus (anterior) and T12 intertransverse space (posterior).
T10–L1 Bilateral Paraspinal hypertonicity: Kidney sympathetics are T11-L1. Parasympathetics are occiput-C2.
What are the different types of casts detected in a urinalysis? (400 pts)
Hyaline casts: Made only of protein. A small number is normal after heavy exercise or dehydration but large amounts can signal kidney stress.
Red blood cell casts: They point to bleeding or swelling inside the kidneys.
White blood cell casts: They signal an infection or inflammation.
Granular casts: Look rough or grainy. They often suggest kidney cell damage or disease.
Fatty casts: Contain fat drops. They can point to severe protein loss through the kidneys.
What are the estimated recovery rates/prognosis of ATN? (400 pts)
Short-Term Recovery: Early removal of the trigger in healthy patients typically leads to full recovery in 1 to 3 weeks.
Critical Illness and Mortality: Severe ATN from sepsis or in ICU patients carries up to a 60% mortality rate.
Chronic Kidney Disease (CKD) Risk: Permanent scarring causes 20% of ATN patients to develop Stage 4 CKD within 6 years.
End-Stage Renal Disease (ESRD) Risk: 22% of biopsy-proven ATN patients progress to complete renal failure requiring dialysis, versus 3% in the general population.
What is the etiology of ATN? (400 pts)
Ischemic ATN: Caused by severe, prolonged renal hypoperfusion due to hypovolemic shock, edematous states, systemic vasodilation, or major surgeries.
Nephrotoxic ATN: Caused by substances directly toxic to renal tubular epithelial cells, including exogenous medications, contrast dyes, and heavy metals or poisons.
Mixed Etiology ATN: Combines severe ischemia and direct toxicity, classically caused by endogenous heme pigments (myoglobin from rhabdomyolysis or hemoglobin from hemolysis) that damage proximal tubules and induce severe vasoconstriction.
What caused the metallic taste in the patient’s mouth? (400 pts)
Uremia caused this metallic taste. Gentamicin toxicity led to tubular necrosis and obstruction, dropping her GFR. Unable to excrete waste, her BUN rose. Excess urea secreted into her saliva is converted by oral bacteria into ammonia, creating the metallic taste (uremic fetor).
Explain how luminal sodium concentrations regulate glomerular filtrations. (400 pts)
Tubuloglomerular Feedback (TGF) at the juxtaglomerular apparatus mediates this regulation. Normally, proximal tubules reabsorb >99% of filtered Na+ and Cl-. Remaining Na+ and Cl- reach the early distal tubule macula densa via NKCC2 cotransporters.
Damaged proximal tubules (e.g., in ATN) fail to reabsorb sodium, delivering high sodium concentrations downstream. Macula densa cells transport this excess sodium, consuming ATP and releasing adenosine. Adenosine binds adjacent afferent arteriole receptors, inducing severe vasoconstriction. Reduced blood flow and glomerular hydrostatic pressure cause GFR to plummet
What are treatment and management options for ATN? (500 pts)
Stop Trigger: Immediately stop offending drugs or correct blood flow loss.
Fluid Management: Administer IV fluids to maintain blood pressure and flush tubule-blocking debris.
Monitor Electrolytes: Track and balance key electrolytes (potassium, calcium, magnesium).
Avoid Toxins: Strictly avoid additional nephrotoxic substances.
Dialysis: Use temporary dialysis for severe fluid overload, uremia, or hyperkalemia unmanageable by medical therapy.
What is the sequelae of ATN? (400 pts)
Long-Term Sequelae (CKD & Fibrosis): Incomplete repair causes TGF-β and collagen secretion by macrophages and fibroblasts, resulting in permanent renal fibrosis and tubular hypertrophy.
Progression to ESRD: ATN leads to permanent kidney loss, with 20% developing stage 4 CKD in 6 years and 22% of biopsy-proven cases progressing to ESRD. Risk is highest with older age, lower initial GFR, and higher proteinuria.
Why do ATN patients experience pitting edema and hypertension? (300 pts)
Fluid Retention: Damaged renal tubular cells cannot regulate or excrete sodium and water, causing volume overload.
Hypertension: Sodium and water retention expands intravascular volume, raising cardiac output and blood pressure.
Pitting Edema: Increased intravascular volume raises capillary hydrostatic pressure, forcing fluid into subcutaneous tissues as symmetric 2+ pitting edema up to her mid-calves.
Calculate the fractions excretion of sodium in the case. (500 pts)
[(Urine Sodium x Serum Creatinine) / (Serum Sodium x Urine Creatinine)] x 100%
Step 1: Multiply her Urine Sodium of 80 by her Serum Creatinine of 2.5, which equals 200.
Step 2: Multiply her Serum Sodium of 136 by her Urine Creatinine of 70, which equals 9,520.
Step 3: Divide the first result (200) by the second result (9,520), which equals 0.021008.
Step 4: Multiply that decimal by 100 to get her final Fractional Excretion of Sodium of 2.1 percent.
Describe how gentamicin toxicity leads to ATN. (400 pts)
Filtration and Absorption: Glomeruli filter gentamicin into tubule fluid, where proximal tubule cells absorb and accumulate it
Organelle Poisoning: Intracellular drug damages mitochondria and lysosomes, disrupting energy and generating reactive oxygen species
Cell Death: Chemical stress induces apoptosis and ferroptosis
Cast Formation and GFR Plunge: Dying cells detach and form muddy brown granular casts that obstruct tubules, dropping GFR and accumulating systemic waste