Nephrology Practice Questions

Q: A 40-year-old man is found to have severe metabolic acidosis with a high anion gap. What is the most likely cause?

Methanol ingestion. ### Explanation **Correct Answer: B. Methanol ingestion** The primary diagnostic step in metabolic acidosis is calculating the **Anion Gap (AG)** using the formula: $Na^+ - (Cl^- + HCO_3^-)$. A normal AG is typically $12 \pm 2$ mEq/L. **Methanol ingestion** causes a **High Anion Gap Metabolic Acidosis (HAGMA)** [1]. When methanol is metabolized by alcohol dehydrogenase, it produces formic acid [2]. These unmeasured organic acid anions accumulate in the blood, replacing bicarbonate and increasing the anion gap [1], [2]. Other common causes of HAGMA are remembered by the mnemonic **MUDPILES** (Methanol, Uremia, DKA, Propylene glycol, Iron/INH, Lactic acidosis, Ethylene glycol, Salicylates). **Why the other options are incorrect:** * **Diarrhea (Option A):** This leads to a loss of bicarbonate-rich intestinal fluids. To maintain electroneutrality, the kidneys retain chloride, resulting in a **Normal Anion Gap Metabolic Acidosis (NAGMA)**, also known as hyperchloremic metabolic acidosis. * **Proximal RTA (Type 2) (Option C):** Caused by a defect in bicarbonate reabsorption in the proximal tubule. It results in NAGMA [4]. * **Distal RTA (Type 1) (Option D):** Caused by a failure of $H^+$ secretion in the distal tubule. It also results in NAGMA [4]. **High-Yield Clinical Pearls for NEET-PG:** 1. **Methanol Toxicity:** Classically presents with "snowfield vision" (optic papillitis) and can lead to permanent blindness or putaminal necrosis on MRI [2]. 2. **Osmolar Gap:** Methanol and Ethylene glycol are the two most common causes of HAGMA that also present with an **elevated Osmolar Gap** [1]. 3. **Treatment:** Fomepizole (inhibits alcohol dehydrogenase) is the preferred antidote; ethanol is an alternative [1]. Hemodialysis is indicated in severe cases [3].

Q: Doughy skin and woody induration of the tongue are seen in which of the following conditions?

Hypernatremia. **Explanation:** **Hypernatremia** (Option B) represents a state of hyperosmolality, typically due to a deficit in total body water relative to sodium. When serum sodium levels rise, water is drawn out of the intracellular and interstitial compartments into the intravascular space to maintain osmotic balance [1]. This profound cellular dehydration leads to characteristic physical findings: * **Doughy Skin:** Unlike the "tenting" seen in simple dehydration, the skin in hypernatremia feels thick and "doughy" due to the loss of intracellular water while maintaining some interstitial volume. * **Woody Induration of the Tongue:** The tongue becomes dry, shriveled, and firm (woody) due to extreme mucosal dehydration. **Incorrect Options:** * **Hyponatremia (A):** Typically presents with signs of cerebral edema (headache, seizures, coma) due to water moving *into* cells [1]. Skin turgor may be decreased if it is hypovolemic hyponatremia, but it does not produce the "doughy" texture. * **Hypokalemia (C) & Hyperkalemia (D):** Potassium imbalances primarily affect neuromuscular and cardiac conduction [2]. Clinical features include muscle weakness, ileus, or arrhythmias, but they do not significantly alter skin or tongue consistency. **Clinical Pearls for NEET-PG:** * **Adipsic Hypernatremia:** Often seen in elderly patients with a diminished thirst mechanism or hypothalamic lesions [2]. * **Correction Rate:** In chronic hypernatremia, the brain produces **idiogenic osmoles** to prevent shrinkage. Rapid correction can lead to **Cerebral Edema**. The goal is to lower sodium by no more than 10–12 mEq/L in 24 hours [1]. * **Key Association:** Always look for "doughy skin" in pediatric cases of severe dehydration or patients with Diabetes Insipidus.

Q: Which of the following is the most likely cause of Acute Renal Failure (ARF) in a patient with a renal failure index less than 1?

Congestive cardiac failure. ### Explanation The **Renal Failure Index (RFI)** is a diagnostic tool used to differentiate between **Prerenal Azotemia** and **Intrinsic Acute Tubular Necrosis (ATN)**. It is calculated as: $RFI = \frac{Urine\ Sodium\ (U_{Na})}{Urine\ Creatinine / Plasma\ Creatinine\ (U_{Cr}/P_{Cr})}$ #### 1. Why Congestive Cardiac Failure (CCF) is Correct An **RFI < 1** (along with a Fractional Excretion of Sodium, $FE_{Na} < 1\%$) indicates **Prerenal Azotemia**. In CCF, there is a decrease in effective arterial blood volume and cardiac output. This leads to renal hypoperfusion [1]. The kidneys, being structurally intact, respond by maximally activating the Renin-Angiotensin-Aldosterone System (RAAS), leading to avid reabsorption of sodium and water. This results in low urinary sodium ($U_{Na} < 20$ mEq/L) and a low RFI. #### 2. Why Other Options are Incorrect * **Acute Glomerulonephritis:** While some cases of early glomerulonephritis can present with low $FE_{Na}$, it is primarily an intrinsic renal pathology [1]. * **Bilateral Acute Pyelonephritis:** This is an inflammatory/infective condition of the renal parenchyma. Once it causes ARF, the tubular ability to concentrate urine and reabsorb sodium is usually impaired, leading to an **RFI > 1**. * **TTP:** This causes renal failure via microangiopathic hemolytic anemia and microthrombi in the renal vasculature (intrinsic damage), typically resulting in an **RFI > 1**. #### 3. Clinical Pearls for NEET-PG * **RFI 1 / $FE_{Na} > 2\%$:** Intrinsic causes (Acute Tubular Necrosis). * **Urine Osmolality:** In Prerenal ARF, urine is concentrated (>500 mOsm/kg); in ATN, it is isosthenuric (~300 mOsm/kg). * **BUN/Creatinine Ratio:** Typically **>20:1** in Prerenal Azotemia due to increased urea reabsorption.

Q: A 45-year-old man experienced a subarachnoid hemorrhage from an intracranial aneurysm 6 years ago. He also developed progressive renal impairment associated with hematuria. What is the likely diagnosis?

Polycystic Kidney Disease (PCKD). ### Explanation The correct diagnosis is **Autosomal Dominant Polycystic Kidney Disease (ADPKD)**. **1. Why ADPKD is correct:** ADPKD is a multisystemic disorder characterized by the growth of numerous cysts in the kidneys, leading to progressive renal failure and hematuria (often due to cyst rupture or stones) [1]. A classic extra-renal manifestation of ADPKD is **intracranial "berry" aneurysms**, typically located in the Circle of Willis. Rupture of these aneurysms leads to **subarachnoid hemorrhage (SAH)**. The combination of progressive renal impairment, hematuria, and a history of SAH is a classic clinical triad for ADPKD in medical examinations [1]. **2. Why the other options are incorrect:** * **Medullary Sponge Kidney:** This involves cystic dilatation of collecting ducts [2]. While it can cause hematuria and stones, it rarely leads to progressive renal failure and has no association with intracranial aneurysms [2]. * **Liddle Syndrome:** A rare genetic disorder causing hypertension and hypokalemia due to overactive epithelial sodium channels (ENaC). It does not cause renal failure or intracranial aneurysms. * **Fanconi Syndrome:** A generalized dysfunction of the proximal tubule leading to the loss of glucose, amino acids, and phosphates in the urine. It presents with rickets/osteomalacia and electrolyte imbalances, not SAH. **3. NEET-PG High-Yield Pearls:** * **Genetics:** Most common cause is a mutation in the **PKD1 gene** (Chromosome 16), which is more severe than PKD2 (Chromosome 4) [1]. * **Extra-renal manifestations:** Hepatic cysts (most common), Berry aneurysms, Mitral Valve Prolapse (MVP), and diverticulosis. * **Diagnosis:** Ultrasonography is the initial screening modality of choice. * **Management:** Tolvaptan (Vasopressin V2 receptor antagonist) can be used to slow disease progression in certain patients.

Q: Primary peritonitis with pneumococcus is associated with which of the following conditions?

Nephrotic syndrome. **Explanation:** **Primary Peritonitis (Spontaneous Bacterial Peritonitis)** in the context of renal disease is a classic association with **Nephrotic Syndrome**, particularly in the pediatric population. [1] **Why Nephrotic Syndrome is the correct answer:** Patients with Nephrotic Syndrome are highly susceptible to infections due to several pathophysiological mechanisms: 1. **Hypogammaglobulinemia:** Massive urinary loss of Immunoglobulin G (IgG). 2. **Complement Deficiency:** Loss of Factor B and Factor D (alternative complement pathway components) in the urine, which impairs the **opsonization** of encapsulated bacteria. [1] 3. **Ascites:** The presence of ascitic fluid acts as a culture medium for bacterial growth. [1] *Streptococcus pneumoniae* (Pneumococcus) is the most common causative organism in these patients, followed by Gram-negative organisms like *E. coli*. **Why other options are incorrect:** * **Lymphomas:** While lymphoma patients are immunocompromised, they are more prone to infections related to T-cell dysfunction or neutropenia (e.g., fungal infections, viral reactivations). They do not typically present with primary pneumococcal peritonitis unless there is associated massive ascites or secondary hypogammaglobulinemia. * **Carcinoids:** Carcinoid tumors primarily cause symptoms via hormone secretion (serotonin). While they can cause "Carcinoid Heart Disease" or fibrosis, they do not have a direct association with pneumococcal peritonitis. **High-Yield Clinical Pearls for NEET-PG:** * **Most common organism overall in SBP (Adult Cirrhosis):** *E. coli*. * **Most common organism in SBP (Nephrotic Syndrome):** *Streptococcus pneumoniae*. * **Diagnostic Gold Standard:** Ascitic fluid absolute neutrophil count (ANC) **>250 cells/mm³**. * **Prophylaxis:** In certain high-risk nephrotic patients, pneumococcal vaccination is recommended to mitigate this specific risk.

Q: Which one of the following is NOT a novel biomarker of acute kidney injury?

β-Trace protein. The diagnosis of Acute Kidney Injury (AKI) has traditionally relied on Serum Creatinine; however, creatinine is a "lagging" marker that only rises after significant loss of GFR [1]. To detect "subclinical AKI" or early tubular damage, several **novel biomarkers** have been identified. [2] **Why β-Trace Protein is the correct answer:** While β-Trace protein (also known as Prostaglandin D2 synthase) is a marker used to estimate GFR and detect CSF leaks, it is primarily considered a marker of **chronic kidney disease (CKD)** and stable renal function rather than an acute marker of tubular injury. It does not rise rapidly enough or specifically enough in response to acute insults to be classified as a "novel biomarker of AKI" in the same category as NGAL or KIM-1. **Analysis of Incorrect Options:** * **NGAL (Neutrophil Gelatinase-Associated Lipocalin):** Often called the "troponin of the kidney," it is the most well-studied novel biomarker. It is produced by thick ascending limb and collecting duct cells and rises within 2–4 hours of injury. * **KIM-1 (Kidney Injury Molecule-1):** A transmembrane protein highly expressed in proximal tubular cells specifically after ischemic or toxic injury. It is an excellent marker for acute tubular necrosis (ATN). * **Cystatin C:** A protease inhibitor produced by all nucleated cells. It is filtered freely and not secreted, making it a more sensitive marker for early changes in GFR than creatinine in the acute setting. **High-Yield Clinical Pearls for NEET-PG:** * **Functional Markers (GFR):** Cystatin C, Proenkephalin A. * **Damage Markers (Tubular):** NGAL, KIM-1, IL-18, L-FABP. * **Cell Cycle Arrest Markers:** [TIMP-2] × [IGFBP7] (marketed as NephroCheck) are the newest markers used to predict the development of moderate-to-severe AKI. * **NGAL** is the earliest marker to rise in post-cardiac surgery AKI.

Question 1

A 40-year-old man is found to have severe metabolic acidosis with a high anion gap. What is the most likely cause?

Accepted Answer

Methanol ingestion

Answer

Diarrhea

Answer

Proximal renal tubular acidosis

Answer

Distal renal tubular acidosis

Question 2

A patient presents with hypotension in a confused state and metabolic alkalosis. Which of the following tests will best suggest the diagnosis?

Accepted Answer

Urine Na+

Answer

Urine pH

Answer

Urine Cl-

Answer

Urine K+

Question 3

A patient presenting with hemoptysis and renal failure with anti-basement membrane antibodies has which of the following conditions?

Accepted Answer

Goodpasture syndrome

Answer

Wegener's granulomatosis

Answer

Churg-Strauss syndrome

Answer

Henoch-Schonlein purpura

Question 4

Doughy skin and woody induration of the tongue are seen in which of the following conditions?

Accepted Answer

Hypernatremia

Answer

Hyponatremia

Answer

Hypokalemia

Answer

Hyperkalemia

Question 5

Which of the following is the most likely cause of Acute Renal Failure (ARF) in a patient with a renal failure index less than 1?

Accepted Answer

Congestive cardiac failure

Answer

Acute glomerulonephritis

Answer

Bilateral acute pyelonephritis

Answer

Thrombotic thrombocytopenic purpura (TTP)

Question 6

Hepatorenal syndrome is characterized by all of the following except?

Accepted Answer

Managed effectively by renal vasodilating agents.

Answer

Reduction in creatinine clearance

Answer

Proteinuria less than 500 mg/d

Answer

Normal intrinsic kidney

Question 7

A 45-year-old man experienced a subarachnoid hemorrhage from an intracranial aneurysm 6 years ago. He also developed progressive renal impairment associated with hematuria. What is the likely diagnosis?

Accepted Answer

Polycystic Kidney Disease (PCKD)

Answer

Medullary Sponge Kidney

Answer

Liddle syndrome

Answer

Fanconi syndrome

Question 8

Primary peritonitis with pneumococcus is associated with which of the following conditions?

Accepted Answer

Nephrotic syndrome

Answer

Lymphomas

Answer

Carcinoids

Answer

None of the above

Question 9

Which of the following conditions is associated with high blood pressure, metabolic alkalosis, and hypokalemia?

Accepted Answer

Liddle’s syndrome

Answer

Gitelman syndrome

Answer

Barter syndrome

Answer

Fanconi’s syndrome

Question 10

Which one of the following is NOT a novel biomarker of acute kidney injury?

Accepted Answer

β-Trace protein

Answer

NGAL

Answer

KIM-1

Answer

Cystatin C

Nephrology — MCQs

Nephrology — MCQs

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