WBR234
| Author | [[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Will Gibson)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Physiology |
| Sub Category | SubCategory::Renal |
| Prompt | [[Prompt::An experiment to measure the filtration fraction in healthy volunteers is conducted. One sample of the available urine and serum values is shown below. If the urine flow is 2.0 ml/min, what is the best approximate filtration fraction?
|
| Answer A | AnswerA::20% |
| Answer A Explanation | AnswerAExp::One could obtain this number by using the ratio of the serum PAH to serum creatinine. However, this does not reflect any standard physiologic parameter. |
| Answer B | AnswerB::30% |
| Answer B Explanation | AnswerBExp::According to the calculation, this is an incorrect answer. |
| Answer C | AnswerC::35% |
| Answer C Explanation | AnswerCExp::According to the calculation, this is an incorrect answer. |
| Answer D | AnswerD::40% |
| Answer D Explanation | AnswerDExp::According to the calculation, this is a correct answer. |
| Answer E | AnswerE::100% |
| Answer E Explanation | AnswerEExp::This number could be achieved by dividing the renal creatinine concentration by the serum creatinine concentration. However, this measure does not reflect any normal physiologic parameter. |
| Right Answer | RightAnswer::D |
| Explanation | [[Explanation::Despite the presence of several parameters, utilization of only creatinine and PAH is required to calculate the filtration fraction.
Filtration fraction (FF) is calculated by the following equation: FF (%) = (GFR / RPF) x 100 GFR = (UCr x V)/PCr = (100 mg/dL x 2 ml/min ) / (1 mg/dL) = 200 mL/min RPF = (UPAH x V)/PPAH = (50 mg/dL x 2 ml/min ) / (0.2 mg/dL) = 500 mL/min FF (%) = (GFR / RPF) x 100 = (200/500) x 100 = 0.4 x 100 = 40% Abbreviations:
Educational Objective: The filtration fraction can be calculated by the following formula: FF (%) = (GFR/RPF) x 100 |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Renal physiology, WBRKeyword::Renal plasma flow, WBRKeyword::Filtration fraction, WBRKeyword::Nephrology, WBRKeyword::Kidney, WBRKeyword::GFR, WBRKeyword::PAH, WBRKeyword::Creatinine |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |
