NMS Q&A Family Medicine

Nephrology 117by creatinine clearance. For example, stage 2 is defined as“kidney damage” (e.g., abnormal urinalysis) with creatinineclearance of 60 to 89 mL/minute/1.73 m 2 (somewhatabove 50% of normal renal function for a person under40 years of age). At this stage, the parathyroid hormonelevels begin to rise because of the renal retention of phosphates(as discussed earlier).Renal failure, stage 3, is defined as creatinine clearancein the range of 30 to 59 mL/minute/1.73 m 2 . Calciumabsorption declines, leading to further secretion of parathormone;lipoprotein activity declines; left ventricularhypertrophy appears; and anemia develops. Stage 4 kidneydisease is defined as creatinine clearance in the rangeof 15 to 29 mL/minute/1.73 m 2 ; end-stage disease shows 15 mL/minute/1.73 m 2 . A completely accurate creatinineclearance requires a measurement of both 24-hoururine creatinine and serum creatinine levels. Serum creatininedoes not begin to rise until renal function has fallenby about 50%. The urinalysis says nothing directly regardingthe status of renal function.9. The answer is E. Decreased production of erythropoietinaccounts for the anemia specific to renal failure. Thus,the anemia is normochromic and normocytic. Iron deficiencyproduces a microcytic, hypochromic anemia,whereas both folic acid and B 12 deficiency cause a macrocyticanemia. The anemia that accompanies renal failureincreases the progression of and the ultimate mortalitythat is due to end-stage kidney disease. Therefore, a criticalpart of the treatment of renal failure is the institutionof exogenous erythropoietin. As implied in Question 6,hemoglobin should be followed as creatinine clearancefalls below 60 mL/minute/1.73 m 2 and hematocrit falls toless than 30% to 35%, whereupon treatment with erythropoietinis started. Recombinant erythropoietin in theform of epoetin alfa is used clinically.10. The answer is E. In and of itself, renal cell carcinomais not a contraindication for contrast media in radiographicstudies. In fact, because the contrast medium isfiltered by the glomeruli and concentrated in the tables, aCT scan with contrast is an excellent modality for diagnosisof cysts and neoplasms. Serum creatinine 5 mg/dL isa contraindication for contrast media because of the dangerof precipitating ARF. In diabetics, the tolerance levelfor serum creatinine is lowered to 2 mg/dL. Even prerenalazotemia (exemplified by the choice showing normal creatininewith elevated BUN) poses a risk for ARF in thepresence of contrast medium. Neither glomerular diseasenor renal cell carcinoma are contraindications for contrastin the absence of other contraindications.11. The answer is A. Magnetic resonance imaging is anexcellent tool for diagnosing neoplasm when contrast inCT scan or intravenous pyelogram is contraindicated. ACT scan without contrast, as implied in the discussion forQuestion 8, is not useful in diagnosing neoplasms; certainly,a plain film is not useful either. Although arteriographyand venography may be useful in evaluating masses,both require contrast.12. The answer is B. Direct toxicity by contrast materialin radiographic imaging is the proximate cause of ARF inthe clinical setting presented. ARF in this case is due toacute tubular necrosis, the cause of 85% of cases of ARF.However, it is not likely to occur unless other causes ofrenal damage are present. The latter include any cause ofischemia, hypovolemia, or hypoxia. These are dehydration,preexisting diabetes, hypotension, sepsis, and prolongedanesthesia with vasodilating anesthetic agents.Other causes of direct nephrotoxicity and acute tubularnecrosis include the presence of aminoglycosides (gentamicinthe most, tobramycin the least potent in thatregard); cyclosporine (used to prevent rejection of transplantedorgans); various antineoplastic agents (e.g., cisplatin);and organic solvents and heavy metals (e.g.,mercury, cadmium, and arsenic). Of cases of ARF, 15% ofthem are caused not by tubular necrosis but by interstitialnephritis. Causes of the latter are generally autoimmunerelated. A recently appreciated contrast medium renaltoxicity is significantly more complex. It is now knownthat gadolinium employed as contrast medium in patientswith GFR 30 mL/minute/1.73 m 2 can cause nephrogenicsystemic fibrosis.13. The answer is D. Hypertension, history of hematuria,and flank mass together are strongly suggestive of polycysticdisease of the kidneys (PCDK). Although anypresentation of hematuria of long duration demands evaluationfor urinary tract neoplasm, most bladder tumorspresent with painless intermittent or persistent hematuria,with a small percentage manifesting irritative bladdersymptoms (frequency or dysuria). Renal cell carcinoma isnotorious for painless hematuria, sometimes over longperiods before becoming diagnosable. However, neitherof the aforementioned cancers present with bilateralmasses. Pancreatic cysts may occur in conjunction withPCDK, as may hepatic and splenic cysts. Of patients withPCDK, 50% have hypertension, often preceding the polycysticmanifestations; 50% of cases will progress to endstagerenal disease by the time the patient reaches the ageof 60 years. Despite hematuria that may be significant,anemia is unusual because PCDK is associated with theproduction of erythropoietin.14. The answer is D. Although a systolic BP 220, a diastolicBP 125, or both constitute a diagnosis of acceleratedhypertension, which is an urgent medical state, thediagnosis of malignant hypertension requires these levelsof BP in association with any of the other choices presentedin the question. Accelerated hypertension is a medicalemergency, requiring BP control to avoid development