Kidney Function Tests — MCQs
Regarding FeNa, which of the following is true?
Which of the following contrast agents is PREFERRED in a patient with renal dysfunction for the prevention of contrast-induced nephropathy?
All should be features of a substance to measure GFR, except?
A patient on atorvastatin presents with myalgia; which test is recommended?
Characteristic of acute Glomerulonephritis is?
Cystatin C levels are used for
What is the best method to estimate the amount of proteinuria in a 2-year-old child with nephrotic syndrome?
What does the measurement of Glomerular Filtration Rate (GFR) help determine in kidney function?
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?
What is the most sensitive diagnostic test for detecting early diabetic nephropathy?
Kidney Function Tests Indian Medical PG Practice Questions and MCQs
Question 1: Regarding FeNa, which of the following is true?
- A. Measurement of FeNa is NOT affected by use of diuretic
- B. FeNa is higher in intrinsic renal failure than pre renal failure (Correct Answer)
- C. FeNa is lower in neonates when compared to children
- D. FeNa is similar in both pre term and term neonate
Explanation: ***FeNa is higher in intrinsic renal failure than pre renal failure*** - In **intrinsic renal failure**, the kidneys lose their ability to conserve sodium effectively, leading to a **higher fractional excretion of sodium (FeNa)**, typically > 2%. - Conversely, in **prerenal failure**, the kidneys avidly reabsorb sodium to compensate for decreased renal perfusion, resulting in a **low FeNa**, usually < 1%. *Measurement of FeNa is NOT affected by use of diuretic* - The use of **diuretics** significantly impacts FeNa by directly inhibiting sodium reabsorption, thus rendering FeNa values unreliable for distinguishing between prerenal and intrinsic acute kidney injury [1]. - When a patient is on diuretics, the FeNa will be artificially elevated, regardless of the underlying cause of kidney injury [1]. *FeNa is lower in neonates when compared to children* - **Neonates** generally have a **higher FeNa** compared to older children because their immature renal tubules are less efficient at reabsorbing sodium. - As the kidneys mature during infancy and childhood, sodium reabsorption improves, leading to lower FeNa values. *FeNa is similar in both pre term and term neonate* - **Preterm neonates** typically have a **higher FeNa** than full-term neonates due to even greater renal immaturity, particularly in tubular function. - Their kidneys are less developed, resulting in a reduced capacity for sodium reabsorption compared to full-term infants.
Question 2: Which of the following contrast agents is PREFERRED in a patient with renal dysfunction for the prevention of contrast-induced nephropathy?
- A. Iso-osmolar contrast (Correct Answer)
- B. High osmolar contrast
- C. Ionic contrast
- D. Low osmolar contrast
Explanation: ***Iso-osmolar contrast*** - **Iso-osmolar contrast agents** (e.g., iodixanol) have an osmolality of ~290 mOsm/kg, which is identical to that of plasma. - **This is the PREFERRED choice** in patients with renal dysfunction as multiple studies demonstrate the lowest risk of contrast-induced nephropathy (CIN). - The iso-osmolar formulation minimizes osmotic stress on renal tubules and reduces the risk of acute kidney injury. - **Current guidelines recommend iso-osmolar agents as first-line** in high-risk patients with pre-existing renal impairment. *Low osmolar contrast* - **Low osmolar contrast agents** have osmolality of 600-900 mOsm/kg, which is significantly lower than high osmolar agents but still 2-3 times higher than plasma. - While **acceptable and safer than high osmolar agents**, they are not as optimal as iso-osmolar contrast for patients with renal dysfunction. - These agents are widely used and represent a reasonable alternative when iso-osmolar agents are not available. *High osmolar contrast* - **High osmolar contrast agents** have osmolality >1400 mOsm/kg (about 5 times that of plasma). - They carry the **highest risk of contrast-induced nephropathy** due to severe osmotic load and direct tubular toxicity. - **Contraindicated or strongly avoided** in patients with pre-existing renal dysfunction. *Ionic contrast* - **Ionic contrast** refers to the chemical structure (dissociates into ions) rather than osmolality. - Can be either high or low osmolar—the ionic nature alone does not determine renal safety. - The critical factor for nephrotoxicity prevention is osmolality, not ionic charge.
Question 3: All should be features of a substance to measure GFR, except?
- A. Freely reabsorbed (Correct Answer)
- B. Not secreted by kidney
- C. Freely filtered across the glomerulus membrane
- D. None of the options
Explanation: ***Freely reabsorbed*** - A substance used to measure GFR should **not be reabsorbed** by the kidney tubules. If it were reabsorbed, the amount excreted in the urine would be less than the amount filtered, leading to an **underestimation of GFR**. - The ideal GFR marker is **neither reabsorbed nor secreted**, ensuring that its excretion rate directly reflects the filtration rate. *Freely filtered across the glomerulus membrane* - For a substance to accurately measure GFR, it must be **freely filtered** from the blood into the Bowman's capsule, without any restriction due to its size or charge. - This ensures that its concentration in the glomerular filtrate is the same as in the plasma, allowing for a direct calculation of the filtration rate. *Not secreted by kidney* - An ideal GFR marker should **not be secreted** by the renal tubules, as active secretion would add to the amount excreted in the urine, leading to an **overestimation of GFR**. - This property, along with not being reabsorbed, ensures that the amount of the substance appearing in the urine solely reflects the amount filtered. *None of the options* - This option is incorrect because there is a definitive feature listed among the choices that is *not* a characteristic of an ideal GFR marker. The ability to be "freely reabsorbed" is a disqualifying trait.
Question 4: A patient on atorvastatin presents with myalgia; which test is recommended?
- A. Liver function test
- B. Blood urea nitrogen
- C. Serum potassium
- D. Creatine kinase (Correct Answer)
Explanation: ***Creatine kinase*** - **Myalgia** in a patient on **atorvastatin** raises concern for **statin-induced myopathy**, which can range from mild muscle aches to severe **rhabdomyolysis** [1]. - **Creatine kinase (CK)** levels are commonly used to assess muscle damage, with significantly elevated levels (e.g., >10 times normal) indicating rhabdomyolysis [1]. *Liver function test* - While atorvastatin can cause **hepatic dysfunction**, **myalgia** is not a primary symptom of liver injury [1]. - **Liver function tests (LFTs)** would be more relevant if the patient presented with jaundice, dark urine, or other signs of liver damage [1]. *Blood urea nitrogen* - **Blood urea nitrogen (BUN)** is a marker of **kidney function**, not directly related to muscle pain or statin-induced myopathy. - While severe **rhabdomyolysis** can lead to **acute kidney injury (AKI)**, BUN would be checked *after* CK levels indicate significant muscle breakdown. *Serum potassium* - **Serum potassium** levels are important for **cardiac and muscle function**, but myalgia itself does not directly indicate a potassium imbalance. - **Hyperkalemia** can occur secondary to severe **rhabdomyolysis** due to the release of intracellular potassium from damaged muscle cells, but CK is the initial diagnostic test for muscle injury.
Question 5: Characteristic of acute Glomerulonephritis is?
- A. Hemoglobinuria
- B. Hyaline cast
- C. RBC cast (Correct Answer)
- D. Broad cast
Explanation: ***RBC cast*** - The presence of **red blood cell casts** in urine is the **hallmark** of glomerulonephritis, indicating glomerular inflammation and hemorrhage [1]. - These casts are formed when red blood cells enter the renal tubules and are molded within the **protein matrix** of the tubule. *Hemoglobinuria* - **Hemoglobinuria** refers to free hemoglobin in the urine, often seen in conditions involving **intravascular hemolysis**, not directly indicative of glomerular damage [2]. - While red blood cells may be present in glomerulonephritis resulting in gross or microscopic hematuria, free hemoglobin in urine is distinct from the presence of red blood cells or RBC casts [2]. *Hyaline cast* - **Hyaline casts** are composed primarily of Tamm-Horsfall protein and can be seen in **healthy individuals**, especially after exercise, or in conditions like dehydration. - Their presence is **non-specific** and does not point directly to acute glomerulonephritis. *Broad cast* - **Broad casts** (or "waxy casts") are larger than typical casts and are associated with **end-stage renal disease** and chronic kidney failure, indicating severely dilated and hypertrophied tubules. - They are not characteristic of the acute inflammation seen in acute glomerulonephritis. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Kidney, pp. 915-916. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Red Blood Cell and Bleeding Disorders, pp. 639-640.
Question 6: Cystatin C levels are used for
- A. Detecting UTI
- B. Estimating GFR (Correct Answer)
- C. Screening for Renal Ca
- D. Estimating difference between CRF and ARF
Explanation: ***Estimating GFR*** - **Cystatin C** is a **proteinase inhibitor** produced by all nucleated cells at a constant rate, and its level in the blood is inversely related to the **glomerular filtration rate (GFR)**. - Unlike **creatinine**, Cystatin C levels are less affected by **muscle mass, diet, or inflammation**, making it a more reliable marker for early and subtle changes in GFR, especially in certain populations. *Detecting UTI* - **Urinary tract infections (UTIs)** are primarily detected through **urinalysis** (presence of **leukocytes, nitrites**, and **bacteria**) and **urine culture**. - **Cystatin C** is a serum marker for renal function and has no direct role in detecting the presence of bacterial infection in the urinary tract. *Estimating difference between CRF and ARF* - Differentiating between **chronic renal failure (CRF)** and **acute renal failure (ARF)** typically involves assessing the **chronicity of symptoms**, trend in **creatinine levels**, and **kidney size** and **echogenicity** on ultrasound. - While Cystatin C can reflect current GFR, it doesn't inherently provide discriminatory power between acute and chronic processes without serial measurements or additional clinical context. *Screening for Renal Ca* - **Renal cell carcinoma (RCC)** screening is primarily done using **imaging techniques** like **ultrasonography, CT, or MRI**, especially in individuals with risk factors or symptoms like **hematuria**. - **Cystatin C** is a marker of kidney function and does not serve as a tumor marker for renal cancer.
Question 7: What is the best method to estimate the amount of proteinuria in a 2-year-old child with nephrotic syndrome?
- A. Single morning spot urine sample for protein/creatinine ratio (Correct Answer)
- B. 24 hr urine protein
- C. Dipstick testing
- D. Microalbuminuria
Explanation: ***Single morning spot urine sample for protein/creatinine ratio*** - The **protein/creatinine ratio** in a single morning spot urine sample correlates well with 24-hour urine protein excretion and is more convenient, especially in children. - This method avoids the difficulties associated with **24-hour urine collection** in young children, such as incomplete or inaccurate collection. *24 hr urine protein* - While considered the gold standard, **24-hour urine collection** is often impractical and unreliable in a 2-year-old due to challenges in complete collection. - Incomplete collections can lead to **underestimation** of proteinuria, making the result inaccurate for diagnosis and monitoring. *Dipstick testing* - **Dipstick testing** provides a qualitative or semi-quantitative estimate of proteinuria but can be affected by urine concentration and pH. - It lacks the precision needed to accurately quantify proteinuria for monitoring treatment response or assessing disease severity in **nephrotic syndrome**. *Microalbuminuria* - **Microalbuminuria** refers specifically to the excretion of albumin in amounts too small to be detected by standard dipstick tests but higher than normal. - This test is primarily used for early detection of **diabetic nephropathy** and is not the primary method for quantifying overt proteinuria in nephrotic syndrome.
Question 8: What does the measurement of Glomerular Filtration Rate (GFR) help determine in kidney function?
- A. Heart rate
- B. Recovery from shock
- C. Stage of kidney disease (Correct Answer)
- D. Blood volume
Explanation: Stage of kidney disease - A low GFR indicates impaired kidney function, helping to classify the severity and stage of chronic kidney disease (CKD) [1]. - Monitoring GFR over time is crucial for assessing disease progression and guiding treatment strategies [1]. *Heart rate* - Heart rate is a measure of cardiac function and is not directly assessed by GFR. - Kidney function can indirectly affect heart rate over time (e.g., in advanced kidney disease with fluid overload), but GFR itself doesn't measure it. *Recovery from shock* - While kidney function is important during shock, GFR primarily measures the kidney's filtration capacity at a given moment. - Recovery from shock involves many physiological parameters beyond just kidney filtration, such as blood pressure and organ perfusion. *Blood volume* - Blood volume is regulated by many mechanisms, including hormonal systems (e.g., renin-angiotensin-aldosterone system) and fluid intake/excretion. - Although kidneys play a role in fluid balance, GFR specifically measures the rate of filtration of blood plasma, not the overall blood volume [1].
Question 9: 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 10: What is the most sensitive diagnostic test for detecting early diabetic nephropathy?
- A. Urine microalbumin test (Correct Answer)
- B. Serum urea level
- C. Serum creatinine level
- D. Urine dipstick test
Explanation: ***Urine microalbumin test*** - This test detects small amounts of **albumin** in the urine, which is often the earliest sign of damage to the kidney's filtration system (glomeruli) in patients with diabetes [1, 5]. - It's a key screening tool for early **diabetic nephropathy** because it can identify kidney damage before significant changes in GFR or serum creatinine occur [1, 5]. *Serum urea level* - **Serum urea** levels only become elevated in advanced kidney disease when the kidneys have lost a substantial portion of their function. - Therefore, it is not sensitive enough to detect **early diabetic nephropathy**. *Serum creatinine level* - **Serum creatinine** levels are used to estimate **glomerular filtration rate (GFR)**, but they are not sensitive indicators of early kidney damage [2]. - Significant **kidney damage** must occur before creatinine levels rise above the normal range [1]. *Urine dipstick test* - A routine **urine dipstick test** only detects larger amounts of protein in the urine (macroalbuminuria or proteinuria). - It is not sensitive enough to detect **microalbuminuria**, which is the hallmark of early diabetic nephropathy [1].
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