WBR0903

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 2 CK
Main Category
Sub Category
Prompt	[[Prompt::A 33 year old male patient known to have diabetes mellitus type 1 on insulin presents to the ER for severe vomiting and abdominal pain. His symptoms started in the afternoon shortly following a lunch meeting his company organized. When he was asked about what he ate throughout this day, he answers that he didn’t eat anything except some egg salad. Upon physical exam, the patient looks pale, his skin and mouth mucosa are dry and the upper abdomen is tender. Vital signs are: temperature of 37 degree Celsius, blood pressure of 100/60 mmHg and heart rate of 100 bpm. Blood results reveal a sodium level of 132 mEq/L. What are the most possible values of spot urine sodium and BUN/creatinine ratio respectively that are expected in this patient’s conditions?]]
Answer A	[[AnswerA::<10 and <20:1]]
Answer A Explanation	[[AnswerAExp::Since the patient is dehydrated his BUN/Creatinine ratio should be high reflecting a low fluid volume in his body. BUN/Creatinine <20:1 is incorrect.]]
Answer B	[[AnswerB::<10 and >20:1]]
Answer B Explanation	AnswerBExp::Since the patient is dehydrated, his spot urine sodium is expected to be low because he is having extrarenal losses of sodium, while his BUN/Creatinine ratio should be high reflecting a low fluid volume in his body.
Answer C	[[AnswerC::>10 and >20:1]]
Answer C Explanation	[[AnswerCExp::Since the patient is dehydrated, his spot urine sodium is expected to be low and not >10.]]
Answer D	[[AnswerD::>20 and >20:1]]
Answer D Explanation	AnswerDExp::Since the patient is dehydrated, his spot urine sodium is expected to be low and not more than 20.
Answer E	[[AnswerE::>20 and <20:1]]
Answer E Explanation	[[AnswerEExp::A spot urine sodium >20 and a BUN/creatinine ratio <20:1 is usually found in the setting of euvolemic patients. Since the patient is dehydrated, his spot urine sodium is expected to be low and not more than 20. Moreover, the patient is dehydrated; therefore, his BUN/Creatinine ratio should be high reflecting a low fluid volume in his body. BUN/Creatinine <20:1 is incorrect.]]
Right Answer	RightAnswer::B
Explanation	[[Explanation::Hyponatremia is defined as a serum sodium concentration < 135 meq/L. Hyponatremia can be caused by several medical conditions. The causes of hyponatremia can be differentiated clinically depending on the volume status of the patient. This patient presents with acute gastrointestinal symptoms following ingestion of eggs suggesting food poisoning, possibly due to staphylococcus toxins. The patient shows dehydration signs upon physical exam and has low blood pressure, both confirming the patient’s low volume status. In this context, the hyponatremia of the patient is most likely resulting from dehydration secondary to gastrointestinal losses through vomiting. Hence, since the patient is dehydrated, his spot urine sodium is expected to be low because he is having extrarenal losses of sodium, while his BUN/Creatinine ratio is high reflecting a low fluid volume in his body. Educational objective: The causes of hyponatremia can be differentiated clinically depending on the volume status of the patient. If a patient is dehydated, his spot urine sodium is expected to be low because he is having extrarenal losses of sodium, while his BUN/Creatinine ratio is high reflecting a low fluid volume in his body. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::Hyponatremia, WBRKeyword::dehydration
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::