WBR0618
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| Author | [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Serge Korjian)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Physiology |
| Sub Category | SubCategory::Renal |
| Prompt | [[Prompt::A researcher is studying the effects of cimetidine, an H2 receptor blocker, on renal clearance mechanisms. He conducts an experiment where he estimates the glomerular filtration rate (GFR) in 20 volunteers first by measuring creatinine clearance then by measuring inulin clearance. He then administers 800 mg of oral cimetidine to the volunteers and notes the change in GFR and clearances of both creatinine and inulin. Which of the following changes are most likely to occur following the oral intake of cimetidine?
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| Answer A | AnswerA::A |
| Answer A Explanation | AnswerAExp::Creatinine secretion does not increase with use of cimetidine. |
| Answer B | AnswerB::B |
| Answer B Explanation | AnswerBExp::Creatinine secretion does not increase with use of cimetidine. |
| Answer C | AnswerC::C |
| Answer C Explanation | AnswerCExp::Cimetidine inhibits tubular secretion of creatinine. As such, creatinine clearance will decrease but calculated GFR based on creatinine will become closer to the true GFR, which is calculated by measuring inulin clearance. |
| Answer D | AnswerD::D |
| Answer D Explanation | AnswerDExp::Inulin clearance is not affected. |
| Answer E | AnswerE::E |
| Answer E Explanation | AnswerEExp::Absolute difference between both eGFRs should decrease. eGFR(creatinine) will be less of an overestimation of the true GFR. It will approach the GFR calculated by inulin clearance. |
| Right Answer | RightAnswer::C |
| Explanation | [[Explanation::The use of creatinine clearance for the estimation of the glomerular filtration rate (eGFR) generally overestimates the true GFR due to the combined filtration and secretion of creatinine along the renal tubules. As such, inulin remains the gold standard for the estimation of the GFR because it is only filtered and not secreted. Cimetidine, an H2 receptor blocker, blocks tubular creatinine secretion. Because cimetidine blocks the tubular secretion of creatinine, the creatinine clearance is decreased. The use of cimetidine allows only the filtration of creatinine to occur by preventing its secretion. Thus, the estimation of GFR based on creatinine clearance is expected to become more accurate with the use of cimetidine and approximate inulin clearance or the true GFR. Inulin clearance is not affected by cimetidine. Educational Objective: Cimetidine blocks the tubular secretion of creatinine, thus decreasing creatinine clearance. As such, creatinine will only be filtered and approximation of eGFR based on creatinine values becomes more accurate and closer to the true GFR. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Inulin, WBRKeyword::Creatinine, WBRKeyword::Cimetidine, WBRKeyword::Filtration, WBRKeyword::eGFR, WBRKeyword::GFR, WBRKeyword::Glomerular filtration rate, WBRKeyword::Creatinine clearance |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |
