Renal Function Tests — MCQs
A child has serum osmolality of 270 mOsm/kg and urine osmolality of 1200 mOsm/kg. What is the most probable diagnosis?
A characteristic feature of nephritic syndrome in children is:
2 year old child with length 85cm and weight of 11kg was found to have serum urea of 49mg/dl, serum creatinine 2mg/dl What is the estimated GFR of this child, as per Schwartz formula?
Calcitriol is formed in:
Which radionuclide is best suited for measuring glomerular filtration rate (GFR)?
A substance has a clearance similar to inulin clearance. How is this substance primarily excreted in urine?
A healthy 22-year-old female medical student with normal kidneys decreases her sodium intake by 50% for a period of 2 months. Which of the following parameters is expected to increase in response to the reduction in sodium intake?
Calculate net filtration pressure with the following data: PGC = 42 mm Hg, πGC = 12 mm Hg, PBC = 16 mm Hg. Assume that no proteins were filtered.
Impaired function of Aquaporin results in
Which substance has the least renal clearance?
Renal Function Tests Indian Medical PG Practice Questions and MCQs
Question 1: A child has serum osmolality of 270 mOsm/kg and urine osmolality of 1200 mOsm/kg. What is the most probable diagnosis?
- A. Nephrogenic diabetes insipidus
- B. Water deprivation
- C. Central diabetes insipidus
- D. SIADH (Correct Answer)
Explanation: SIADH - In SIADH (Syndrome of Inappropriate Antidiuretic Hormone), there is excessive ADH secretion, leading to water retention, low serum osmolality (dilute blood), and concentrated urine. [1] - The serum osmolality of 270 mOsm/kg is low-normal/mildly low [3], while the urine osmolality of 1200 mOsm/kg is very high [1], indicating the kidneys are inappropriately conserving water and concentrating urine despite diluted plasma. Nephrogenic diabetes insipidus - This condition involves the kidneys being unable to respond to ADH [2], leading to the excretion of large volumes of dilute urine despite dehydration. - While serum osmolality might be high due to dehydration, urine osmolality would be low (dilute), contrary to the given values. Water deprivation - In water deprivation, the body compensates by releasing ADH, which leads to concentrated urine to conserve water and a high serum osmolality. - Here, the serum osmolality is low-normal, which does not align with the expected high serum osmolality seen in water deprivation. Central diabetes insipidus - Characterized by the lack of ADH production by the pituitary gland [2], resulting in the excretion of large volumes of dilute urine. - Patients with central DI would typically have high serum osmolality (due to water loss) and low urine osmolality (dilute urine), which is the opposite of the given values.
Question 2: A characteristic feature of nephritic syndrome in children is:
- A. WBC casts in urine
- B. Albumin in urine
- C. Lipid casts in urine
- D. RBC casts in urine (Correct Answer)
Explanation: ***RBC casts in urine*** - The presence of **red blood cell (RBC) casts** in urine is a **pathognomonic sign** of **glomerulonephritis**, which is the underlying pathology in nephritic syndrome. - This indicates **glomerular inflammation** and bleeding, where RBCs leak through damaged glomeruli and are molded into casts within the renal tubules. *WBC casts in urine* - **White blood cell (WBC) casts** are characteristic of **pyelonephritis** (kidney infection) or other severe interstitial nephritis, indicating inflammation within the renal tubules. - While infection can sometimes accompany nephritic syndrome, WBC casts are not a primary diagnostic feature of the syndrome itself. *Lipid casts in urine* - **Lipid casts** and **fatty oval bodies** are typically associated with **nephrotic syndrome**, resulting from significant proteinuria and hyperlipidemia. - They signify severe disruption of glomerular filtration leading to lipid excretion, which is not the defining feature of nephritic syndrome. *Albumin in urine* - While **proteinuria (albumin in urine)** is present in nephritic syndrome, it is a non-specific finding and is also a hallmark of **nephrotic syndrome**, where it is much more severe. - The *quality* of the proteinuria (e.g., whether it contains RBCs) is more indicative for differentiating nephritic from nephrotic syndrome.
Question 3: 2 year old child with length 85cm and weight of 11kg was found to have serum urea of 49mg/dl, serum creatinine 2mg/dl What is the estimated GFR of this child, as per Schwartz formula?
- A. 48
- B. 9
- C. 19 (Correct Answer)
- D. 90
Explanation: ***19*** - The **Schwartz formula** for estimating GFR in children is: **GFR = k × (length in cm / serum creatinine in mg/dL)**. - For a 2-year-old child, the constant **k is typically 0.45**. Therefore, GFR = 0.45 × (85 cm / 2 mg/dL) = 0.45 × 42.5 = 19.125, which rounds to **19 mL/min/1.73m²**. - This GFR value indicates **moderate to severe chronic kidney disease** in a child. *48* - This value is likely obtained if an incorrect **k constant** was used (such as k = 0.55 for older children) or if there was a calculation error. - A GFR of 48 mL/min/1.73m² would indicate **moderate chronic kidney disease (Stage 3)**, but the calculation using the appropriate k value does not support this. *9* - This value would result from using an incorrect k value (possibly dividing 0.45 by 2) or making an **arithmetic error** in the calculation. - A GFR of 9 mL/min/1.73m² would suggest **severe kidney failure (Stage 5 CKD)**, which is inconsistent with the provided parameters when calculated correctly. *90* - A GFR of 90 mL/min/1.73m² or higher generally indicates **normal kidney function**. - This value is significantly higher than what would be calculated using the Schwartz formula with the given creatinine level of 2 mg/dL, which indicates significant kidney impairment in a child.
Question 4: Calcitriol is formed in:
- A. Glomerulus
- B. Bowman's capsule
- C. PCT (Correct Answer)
- D. DCT
Explanation: ***PCT*** - The final step in calcitriol (active vitamin D) synthesis, 1-alpha hydroxylation, primarily occurs in the **proximal convoluted tubule (PCT)** cells of the kidney. - This enzymatic step converts **25-hydroxyvitamin D** into the potent hormone **1,25-dihydroxyvitamin D (calcitriol)**, which regulates calcium and phosphate homeostasis. *Glomerulus* - The **glomerulus** is primarily responsible for **filtering blood** to form ultrafiltrate, not for hormone synthesis. - While vitamin D precursors are filtered, the enzymatic conversion to calcitriol does not occur here. *Bowman's capsule* - **Bowman's capsule** surrounds the glomerulus and collects the filtered fluid, acting as a passive receiver. - It plays no direct role in the synthesis or metabolism of vitamin D. *DCT* - The **distal convoluted tubule (DCT)** is involved in fine-tuning reabsorption of ions like calcium and sodium, responding to hormones. - It is not the primary site for the **1-alpha hydroxylation** required for calcitriol synthesis.
Question 5: Which radionuclide is best suited for measuring glomerular filtration rate (GFR)?
- A. DTPA (Correct Answer)
- B. DMSA
- C. EDTA
- D. Ortho-Iodohippurate
Explanation: ***DTPA*** - **DTPA (⁹⁹ᵐTc-DTPA)** is cleared almost exclusively by **glomerular filtration**, making it an excellent marker for GFR measurement. - Its rapid plasma clearance correlates well with **inulin clearance**, which is the gold standard for GFR. - **⁹⁹ᵐTc labeling** provides superior imaging properties, ready availability from generators, and optimal gamma energy for detection. *DMSA* - **DMSA (⁹⁹ᵐTc-dimercaptosuccinic acid)** primarily binds to the **renal cortex** and is used to assess renal parenchymal function and anatomy. - It does not accurately reflect GFR because it is mainly handled by **tubular uptake**, not glomerular filtration. *Ortho-Iodohippurate* - **Ortho-Iodohippurate (¹³¹I-OIH or ⁹⁹ᵐTc-MAG3)** is predominantly cleared by **tubular secretion**, making it a good measure of **effective renal plasma flow (ERPF)**. - While it provides information on renal function, it is not suitable for direct GFR assessment. *EDTA* - **EDTA (⁵¹Cr-EDTA)** is also cleared by glomerular filtration and can accurately measure GFR, particularly used in Europe. - However, **DTPA is preferred** due to the advantages of **⁹⁹ᵐTc labeling** (better availability, imaging properties, and lower radiation dose) compared to **⁵¹Cr labeling**. - Both are valid GFR markers, but DTPA is more commonly used in routine clinical practice.
Question 6: A substance has a clearance similar to inulin clearance. How is this substance primarily excreted in urine?
- A. Tubular Secretion
- B. Glomerular filtration (Correct Answer)
- C. Vascular leakage
- D. Both tubular secretion and glomerular filtration
Explanation: ***Glomerular filtration*** - **Inulin** is a gold standard for measuring **glomerular filtration rate** (GFR) because it is freely filtered by the glomeruli and is neither reabsorbed nor secreted by the renal tubules. - Therefore, a substance with clearance similar to inulin is primarily excreted via **glomerular filtration**. *Tubular Secretion* - If a substance were primarily excreted by tubular secretion, its clearance would be **higher than the GFR**, as secretion adds more of the substance to the urine than filtration alone. - This mechanism is characteristic of substances like **para-aminohippurate (PAH)**, which is used to measure renal plasma flow. *Vascular leakage* - **Vascular leakage** is not a normal mechanism of substance excretion in the urine. - It refers to the abnormal passage of fluid and macromolecules from blood vessels into tissues, often seen in conditions like inflammation or sepsis, and does not directly contribute to renal clearance. *Both tubular secretion and glomerular filtration* - If a substance were excreted by both **tubular secretion and glomerular filtration**, its clearance would also be **higher than the GFR**, similar to substances that undergo significant tubular secretion. - The fact that its clearance is *similar* to inulin specifically points to filtration as the predominant and almost exclusive mechanism.
Question 7: A healthy 22-year-old female medical student with normal kidneys decreases her sodium intake by 50% for a period of 2 months. Which of the following parameters is expected to increase in response to the reduction in sodium intake?
- A. Atrial natriuretic peptide release
- B. Extracellular fluid volume
- C. Arterial pressure
- D. Renin release (Correct Answer)
Explanation: ***Renin release*** - A reduction in **sodium intake** leads to decreased extracellular fluid volume and **reduced renal perfusion pressure**, which stimulates **renin release** from the juxtaglomerular cells. - Renin initiates the **renin-angiotensin-aldosterone system (RAAS)**, leading to **angiotensin II** formation and increased **aldosterone** secretion, aimed at sodium and water retention. *Atrial natriuretic peptide release* - **Atrial natriuretic peptide (ANP)** release is stimulated by **atrial stretch** due to increased blood volume and pressure, which would decrease with reduced sodium intake. - Therefore, ANP release would likely **decrease** or remain unchanged, not increase, in response to chronic sodium restriction. *Extracellular fluid volume* - A decrease in sodium intake directly leads to a **reduction in total body sodium**, which is the primary determinant of **extracellular fluid volume**. - The body attempts to maintain fluid balance, but chronic sodium restriction will ultimately lead to a **decrease** in extracellular fluid volume as the kidneys excrete less water to match the lower sodium intake. *Arterial pressure* - Reduced sodium intake typically leads to a **decrease in extracellular fluid volume** and **cardiac output**, which in turn causes a **reduction in arterial blood pressure**. - The activation of the RAAS aims to mitigate this drop but usually does not fully compensate to increase pressure above baseline in this scenario.
Question 8: Calculate net filtration pressure with the following data: PGC = 42 mm Hg, πGC = 12 mm Hg, PBC = 16 mm Hg. Assume that no proteins were filtered.
- A. 14 mm Hg (Correct Answer)
- B. 28 mm Hg
- C. Data not sufficient
- D. 34 mm Hg
Explanation: ***14 mm Hg*** - The **net filtration pressure (NFP)** is calculated using the formula: **NFP = (PGC - PBC) - πGC**. - Plugging in the given values: (42 mmHg - 16 mmHg) - 12 mmHg = 26 mmHg - 12 mmHg = **14 mmHg**. *28 mm Hg* - This answer likely results from an incorrect application of the NFP formula, such as adding the oncotic pressure instead of subtracting it, or miscalculating the difference between hydrostatic pressures. - For example, if both hydrostatic and oncotic pressures were added (42 + 12 + 16), it would yield a much higher number, or if the subtraction was done incorrectly. *Data not sufficient* - All necessary variables for calculating the NFP are provided: **glomerular hydrostatic pressure (PGC)**, **glomerular oncotic pressure (πGC)**, and **Bowman's capsule hydrostatic pressure (PBC)**. - The assumption that "no proteins were filtered" simplifies the calculation, confirming that sufficient data is available. *34 mm Hg* - This result would occur if the oncotic pressure in Bowman's capsule (πBC) was incorrectly considered, or if a different formulation of the NFP calculation was used. - Given that **πBC is assumed to be zero** (as no proteins are filtered into Bowman's capsule), any calculation that leads to 34 mmHg is likely based on an error in applying the formula, such as adding **πGC** instead of subtracting it from the hydrostatic pressure difference.
Question 9: Impaired function of Aquaporin results in
- A. Bartter syndrome
- B. Liddle syndrome
- C. Cystic fibrosis
- D. Nephrogenic DI (Correct Answer)
Explanation: ***Nephrogenic DI*** - **Aquaporin-2** (AQP2) is crucial for water reabsorption in the renal collecting ducts, regulated by **vasopressin (ADH)**. - Impaired AQP2 function, often due to genetic mutations or acquired conditions, prevents the kidneys from concentrating urine, leading to **nephrogenic diabetes insipidus (DI)**. *Bartter syndrome* - Bartter syndrome is a rare inherited renal tubular disorder caused by defects in the **sodium-potassium-chloride cotransporter (NKCC2)** or related channels in the thick ascending limb of the loop of Henle. - This leads to salt wasting, hypokalemia, metabolic alkalosis, and hyperreninemia, but is **not related to aquaporin dysfunction**. *Liddle syndrome* - Liddle syndrome is a rare genetic disorder characterized by excessive activity of the **epithelial sodium channel (ENaC)** in the collecting ducts. - This leads to increased sodium reabsorption, hypertension, hypokalemia, and metabolic alkalosis, not directly related to aquaporin function. *Cystic fibrosis* - Cystic fibrosis is an autosomal recessive genetic disorder primarily affecting the **CFTR (cystic fibrosis transmembrane conductance regulator) channel**, which is involved in chloride transport. - This impairment leads to thick, sticky mucus in various organs, particularly the lungs and pancreas, and is unrelated to aquaporin function.
Question 10: Which substance has the least renal clearance?
- A. Glucose (Correct Answer)
- B. Inulin
- C. Urea
- D. Creatinine
Explanation: ***Glucose (Correct Answer)*** - Under normal physiological conditions, **glucose is almost completely reabsorbed** in the proximal tubule of the nephron, leading to a **renal clearance of nearly zero**. - While glucose is freely filtered by the glomerulus, the extensive reabsorption mechanisms (via SGLT2 and SGLT1 transporters) ensure that virtually no glucose appears in the urine under normal circumstances. - This makes glucose the substance with the **least renal clearance** among the given options. *Inulin (Incorrect)* - **Inulin** is freely filtered by the glomerulus but is neither reabsorbed nor secreted by the renal tubules. - Its renal clearance equals the **glomerular filtration rate (GFR)** (~125 mL/min), making it an ideal marker for GFR measurement. - Inulin has a **much higher clearance than glucose**. *Urea (Incorrect)* - **Urea** is filtered by the glomerulus, and approximately **50% of the filtered urea** is reabsorbed in the renal tubules, primarily in the proximal tubule and medullary collecting duct. - Its clearance (~60-70 mL/min) is lower than GFR but still **significantly higher than glucose clearance**. *Creatinine (Incorrect)* - **Creatinine** is freely filtered by the glomerulus and is also **secreted by the renal tubules** (approximately 10-20% secreted). - This secretion means its renal clearance (~130-140 mL/min) is slightly **higher than the actual GFR**. - Despite this, creatinine is commonly used as an estimate of GFR due to its relatively stable production and ease of measurement.
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