A 20-year-old male college student is found passed out in th

[kailash]

A 20-year-old male college student is found passed out in the stairwell of his dormitory, unresponsive to pain or verbal stimuli. No further history is obtainable from the patient, and no other dormitory residents are able to give any additional history. The initial vital signs at the site are: blood pressure 110/58 mm Hg, pulse 78/min, and respirations 16/min. The ambulance technician gives 2 mg of naloxone, with very little response. The patient is then transported to the nearby emergency room. The patient appears to be a disheveled male with alcohol on his breath. The patient is responsive and cooperative to commands; however, he has difficulty with answering questions. The remainder of the examination is unremarkable. Initial laboratory studies reveal:

Sodium 132 mEq/L; potassium 5.4 mEq/L; bicarbonate 20 mEq/L; chloride 96 mEq/L; BUN 34 mg/dL; creatinine 2.9 mg/dL; glucose 108 mg/dL; alcohol level 9 mg/dL (low).

Urine dipstick is negative for leukocytes, nitrites, and blood.

Which of the following tests would you order next to help diagnose the cause of this patient's acute renal failure?

(A) Urine specific gravity
(B) Urine fractional excretion of sodium
(C) CT scan of abdomen and pelvis
(D) Serum osmolality
(E) Urine myoglobin

[kailash]

answer is D

This patient is most likely intoxicated with an alcohol that is not predominantly ethanol. The clue to this diagnosis is a person who appears drunk with alcohol on his breath but in whom the ethanol level is low. Another clue to the presence of a toxic alcohol is a metabolic acidosis with an elevated anion gap. This patient has an anion gap of 16, which is elevated, and a calculated serum osmolality of 282.



Using the serum osmolality, one can calculate the serum osmolar gap. If the measured serum osmolality were significantly higher than what you calculate with the formula described above, it would be highly suggestive of an additional osmolar particle, such as methanol or ethylene glycol. The fact that there is renal failure is by far more consistent with ethylene glycol poisoning.

Another clue to this diagnosis (not present in this case) would be the presence of crystals in the urine or a low calcium level. The urine dipstick in patients with rhabdomyolysis should be positive for blood, but they should also have a microscopic examination that doesn't show red cells. There is no point in getting a urine myoglobin level in a patient whose dipstick is negative for blood. The urine fractional excretion of sodium (FeNa) is used to help distinguish between prerenal azotemia from decreased renal perfusion, compared with azotemia from a problem intrinsic to the kidney itself.. A FeNa <1% is consistent with prerenal azotemia, and a FeNa >1% is from problems intrinsic to the kidney itself. The urine specific gravity can give an approximation of the urine osmolality. Prerenal has a high urine specific gravity. What we need, however, is a serum osmolality. A CT scan or ultrasound of the kidney is useful to help diagnose an obstruction of the urinary system