This page is dedicated to organizing various examples of standardized exam questions whose answer is acute tubular necrosis (ATN). While this may seem a odd practice, it is useful to see multiple examples of how ATN will be characterized on standardized exams (namely the boards and the shelf exams). This page is not meant to be used as a tradition question bank (as all of the answers will be the same), however seeing the classic “test” characterization for a disease is quite valuable.
KEY CHARACTERISTICS OF THIS CONDITION (ON EXAMS)
When it comes to standardized exams, each condition has its own “code” marked by key buzzwords, lab findings, clues, etc. If you are well versed in this code you will be able to more quickly identify the condition that is being discussed, and get the right answer on the exam you are taking. Below is the “code” for ATN.
- Decreased urine output may be noticed by the patient
- Recent medication usage: aminoglycosides are a common cause. (Amikacin, Gentamicin).
- Recent episode of hypotension/cardiac arrest: ischemia to the kidney can be responsible.
- Oliguria can occur (less then 400 mL of urine in 24 hours), or noticeable decreased urine output.
- Acute renal failure: can be demonstrated by elevated creatinine.
- Brown granular casts: are classic on the UA for ATN (“muddy brown” casts is a common buzzword used)
- Histological signs: tubular re-epiteliazation can be seen in the recovery phase of this condition.
- Elevated FENa: patients will have difficulty resorbing sodium due to nephron damage (which increases the fraction of sodium that is excreted in the urine).
Question # 1
Two weeks after a 57 year old male patient is admitted to the hospital for the treatment of an unexplained fever, he develops acute renal failure. His current medications include heparin, lisniopril, naproxen, and amikacin. A physical exam shows 2+ pitting edema in the lower extremities. A urinalysis reveals the presence of a few WBCs, epithelial cells, and many muddy brown casts. What is the likely diagnosis in this patient?
Explanation # 1
Acute renal failure + aminoglycoside usage (amikacin) + muddy brown casts = ATN
Question # 2
A 25 Year old male is brought to the emergency room after being involved in an automobile collision. Soon after arrival his blood pressure can no longer be obtained. Fluid resuscitation is begun, and blood products are given to the patient until his blood pressure is returned to normal values. He undergoes a laporotomy that shows a splenetic laceration which requires splenectomy to control the bleeding. Over the course of the next day, the patient’s urine output is 300 mL. What is the likely cause for this decreased urine output in this patient?
Explanation # 2
Recent episode of extreme hypotension + oliguria = ATN (secondary to renal ischemia)
Question # 3
A 23 year old female comes to her primary care physician because she has noticed that for the past few days she has not been urinating as much as usual. She is concerned because she has been drinking “plenty of water” and does not understand why she is not “peeing it all out”. She recently underwent an appendectomy for a perforated appendix 18 days ago, for which she received IV gentamicin for 2 weeks. A physical exam is unremarkable and her labs are listed below:
- BUN: 37 mg/dL
- Creatinine: 3.1 mg/dL
- Urine specific gravity: 1.011
- Urine protein: 2+
- Urine sodium: 28 mEq/L
- Urine Casts: brown granular
What is the likely diagnosis in this patient?
Explanation # 3
Recent aminoglycoside usage (gentamicin) + decreased urine output + increased creatinine + brown granular casts in urine = ATN
Question # 4
A 45 year old male is brought to the hospital after being found unconscious in the street. He smells of hard alcohol. His temperature is 96.3°F, blood pressure is 85/50 mm Hg, and pulse is 115 ppm. He is unresponsive to verbal commands, but responds to painful stimuli. He is resuscitated with IV fluids, and while his mental status begins to improve, he starts to complain of flank pain, and the medical team notices that he begins to have decreased urine output. A renal biopsy is performed and shows the presence of degeneration of proximal renal tubules. What is the likely diagnosis in this patient?
Explanation # 4
Episode of hypotension + decreased urine output + signs of tubular necrosis on kidney biopsy = ATN
Question # 5
A 67 year old male is hospitalized with an acute myocardial infraction. Upon admission he goes into cardiac arrest, and then is resuscitated successfully. Soon after this episode, the managing medical team notices that his urine production decreases below 400 mL/day. A physical exam is unremarkable and lab results are shown below:
- Sodium: 133 mEq/L
- Potassium: 4.1 mEq/L
- Chloride: 95 mEq/L
- Bicarbonate: 25 mEq/L
- BUN: 28 mg/dL
- Creatinine: 2.6 mg/dL***
A urine sediment demonstrates the presence of muddy brown casts. What is the likely diagnosis in this patient?
Explanation # 5
Period of hypotension/poor renal perfusion (cardiac arrest) + oliguria + increased creatinine + muddy brown casts in urine = ATN
Question # 6
A 35 yea told male is hospitalized with internal bleeding and multiple fractures after he is kicked off of a ill tempered horse that he was riding. He is hypotensive upon arriving to the hospital, but then is successfully resuscitated with IV fluids and taken to the operating room for a right femoral fracture fixation procedure. He is stable during the course of the operation, and his postoperative course is unremarkable except for the development of oliguria on his second day after the procedure. Currently his vitals are within normal limits. A renal biopsy is performed and shows the presence of tubular re-epithelization. What condition did this patient suffer from?
Explanation # 6
Period of hypotension + oliguria + tubular re-epithelization seen on renal biopsy = ATN
Question # 7
A 50 year old male is brought to the emergency room because he has been experiencing crushing chest pain that radiates to his jaw and arm. An EKG and an elevated troponin level reveal that this patient is suffering from a myocardial infarction. A few hours after he is admitted to the hospital he has a cardiac arrest. Resuscitation efforts are successful after a period of 25 minutes. Soon after he is resuscitated the medical team notices that his urine outputs drop dramatically. Lab studies also reveal sharp rises in his BUN and creatinine concentrations. What is this patient likely suffering from?
Explanation # 7
Period of hypotension/poor renal perfusion (cardiac arrest) + oliguria + increased creatinine = ATN
Question # 8
A 75 year old male is admitted to the hospital for the treatment of a severe pneumonia. Since his admission his renal function has been progressively worsening. Upon admission his blood pressure was 80/45 mg/Hg, and his BUN was 12 mg/dL and creatinine was 0.7 mg/dL. The patient was resuscitated with IV fluids successfully, and has been started on antibiotics (ceftriaxone and azithromycin). Now 2 days later, the patient’s blood pressure is within normal limits, however his BUN is 34 mg/dL and creatinine is 2.1 mg/dL. His urine output is also 320 mL/24 h. A urinalysis reveals the presence of muddy brown casts. What is this patient’s diagnosis?
Explanation # 8
Period of hypotension + oliguria + increased creatinine + muddy brown casts on urinalysis = ATN
Question # 9
A 75 year old male has decreased urine output a couple of days after he is admitted to the hospital for the treatment of cholecystitis. His chart reveals that his urine output has been 12 ml/h over the past 3 hours. He is currently receiving IV antibiotics (cefoxitin and gentamicin) for the treatment of a gram-negative bacteria that was discovered upon his admission. His temperature is currently 101.3°F, pulse is 115/min, respirations are 20/min, and his blood pressure is 85/60 mm Hg. An abdominal exam reveals right upper quadrant tenderness, and the rest of his physical exam is non-contributory. Trending his creatinine reveals that his serum concentration has increased from 1.2 mg/dL to 2.5 mg/dL over the course of 2 days. What is the likely diagnosis in this patient?
Explanation # 9
Recent aminoglycoside usage (gentamicin) + period of hypotension + decreased urine output + increased creatinine = ATN
TESTABLE FACTS ABOUT THIS CONDITION (BEYOND ITS IDENTIFICATION)
Many questions on standardized exams go beyond simply recognizing the underlying condition. Often there are specific testable facts regarding some aspect of the disease’s pathophysiology/management/clinical implications that are commonly asked. Some of these are listed below:
- Area of nephron most susceptible to ATN: the proximal convoluted tubule is particularly susceptible to ATN.
Page Updated: 01.22.2017