MEDICINE NEPHROLOGY PRACTICE
QUESTIONS AND SOLUTIONS 2026
COMPLETE LEARNING RESOURCE
◉ Postrenal AKI
Answer: AKI resulting from urinary tract obstruction from prostatic
hypertrophy, crystallization of drugs or obstructive proteins. Clinical
presentation: lower abdominal pain, restless, anuria. Delirium,
listlessness, anorexia.
◉ Glomerular Filtration Rate (GFR)
Answer: The amount of filtrate formed per minute by the two
kidneys combined; a normal value is 60-90 mL/min. An estimation
of it is based on serum creatinine level, sex, age, and weight. CKD-
EPI is more accurate in approximation.
◉ Initial Assessment of AKI
Answer: *Initial Assessment of AKI*
• CBC with differential (peripheral eosinophilia)
• BMP (Na+, K+)
• BUN to Cr ratio
○ > 20:1 is suggestive of prerenal
,○ 10-20:1 is suggestive of postrenal
○ < 10:1 is suggestive of intrarenal
• FENa% (fractional excretion of sodium)
• UA: urine color/quality, sediment (RBCs, muddy brown,
eosinophils, lipid casts)
• Urine osmolarity
• Complement levels, ANA panel
• Imaging: Renal U/S, CT, Abd/pelvis, Bladder U/S
• Biopsy
◉ Blood Urea Nitrogen (BUN)
Answer: A measure of the mass of urea nitrogen, making it an
indirect measure of urea in the blood. Urea is formed in the liver as
an end product of protein metabolism and is excreted in the urine by
the kidneys. Therefore, it is directly related to the metabolic function
of the liver and the excretory function of the kidney. Levels can be
increased with decreased GFR, increased protein intake, or GI bleed.
Levels can be decreased with malnutrition/liver failure. Tends to be
more variable than Cr. Unlike Cr, BUN is in some cases reabsorbed in
the PCT based on the cause of kidney injury, leading to the helpful
diagnostic tool, the BUN/Cr ratio. Once Cr is in the filtrate, it will be
in the urine.
◉ Creatinine (Cr)
, Answer: The lab of choice to evaluate/monitor kidney function. It is
a normal catabolic product of creatine in skeletal muscle in the body,
which generally occurs at a steady rate. Production quantity is
determined by skeletal muscle mass. Constant in most people
(though this can be affected by diet/supplementation) --> and
therefore serum Cr concentration remains the same. Directly
proportional to the GFR (once in the filtrate, it never gets
reabsorbed).
◉ BUN:Cr Ratio
Answer: Ratio of creatinine to BUN level. It is very frequently used to
help assess the cause of an AKI.
○ > 20:1 is suggestive of prerenal
○ 10-20:1 is suggestive of postrenal
○ < 10:1 is suggestive of intrarenal
◉ > 20:1
Answer: A BUN:Cr ratio of _____:_____ is indicative of an AKI
secondary to a prerenal cause.
◉ < 10:1
Answer: A BUN:Cr ratio of _____:_____ is indicative of an AKI
secondary to an intrinsic cause.
QUESTIONS AND SOLUTIONS 2026
COMPLETE LEARNING RESOURCE
◉ Postrenal AKI
Answer: AKI resulting from urinary tract obstruction from prostatic
hypertrophy, crystallization of drugs or obstructive proteins. Clinical
presentation: lower abdominal pain, restless, anuria. Delirium,
listlessness, anorexia.
◉ Glomerular Filtration Rate (GFR)
Answer: The amount of filtrate formed per minute by the two
kidneys combined; a normal value is 60-90 mL/min. An estimation
of it is based on serum creatinine level, sex, age, and weight. CKD-
EPI is more accurate in approximation.
◉ Initial Assessment of AKI
Answer: *Initial Assessment of AKI*
• CBC with differential (peripheral eosinophilia)
• BMP (Na+, K+)
• BUN to Cr ratio
○ > 20:1 is suggestive of prerenal
,○ 10-20:1 is suggestive of postrenal
○ < 10:1 is suggestive of intrarenal
• FENa% (fractional excretion of sodium)
• UA: urine color/quality, sediment (RBCs, muddy brown,
eosinophils, lipid casts)
• Urine osmolarity
• Complement levels, ANA panel
• Imaging: Renal U/S, CT, Abd/pelvis, Bladder U/S
• Biopsy
◉ Blood Urea Nitrogen (BUN)
Answer: A measure of the mass of urea nitrogen, making it an
indirect measure of urea in the blood. Urea is formed in the liver as
an end product of protein metabolism and is excreted in the urine by
the kidneys. Therefore, it is directly related to the metabolic function
of the liver and the excretory function of the kidney. Levels can be
increased with decreased GFR, increased protein intake, or GI bleed.
Levels can be decreased with malnutrition/liver failure. Tends to be
more variable than Cr. Unlike Cr, BUN is in some cases reabsorbed in
the PCT based on the cause of kidney injury, leading to the helpful
diagnostic tool, the BUN/Cr ratio. Once Cr is in the filtrate, it will be
in the urine.
◉ Creatinine (Cr)
, Answer: The lab of choice to evaluate/monitor kidney function. It is
a normal catabolic product of creatine in skeletal muscle in the body,
which generally occurs at a steady rate. Production quantity is
determined by skeletal muscle mass. Constant in most people
(though this can be affected by diet/supplementation) --> and
therefore serum Cr concentration remains the same. Directly
proportional to the GFR (once in the filtrate, it never gets
reabsorbed).
◉ BUN:Cr Ratio
Answer: Ratio of creatinine to BUN level. It is very frequently used to
help assess the cause of an AKI.
○ > 20:1 is suggestive of prerenal
○ 10-20:1 is suggestive of postrenal
○ < 10:1 is suggestive of intrarenal
◉ > 20:1
Answer: A BUN:Cr ratio of _____:_____ is indicative of an AKI
secondary to a prerenal cause.
◉ < 10:1
Answer: A BUN:Cr ratio of _____:_____ is indicative of an AKI
secondary to an intrinsic cause.
