Renal Pathophysiology

CHAPTER 8 Urinalysis and Approach to the Patient With Renal Dysfunction


in the urine in normal subjects. How this occurs is not clear, but alterations in renal hemodynamics may play a contributory role. The frequency of transient urinary abnormalities was illustrated in a study of 1,000 young men who had yearly urinalyses between the ages of 18 and 33 years. Hematuria was seen in 39% on at least one occasion and in 16% on two or more occasions in the absence of any known disease in almost all subjects.

Acute Versus Chronic Renal Disease

CASE PRESENTATION-2 A 72-year-old man has a 20-year history of type 2 diabetes and hypertension. His baseline creatinine is 1.6 mg/dL with an estimated glomerular filtration rate (eGFR) of 45 mL/min. His medications include losartan (an angiotensin receptor blocker) and empagliflozin (an SGLT2i). He develops nausea, vomiting, and diar rhea due to a viral illness. Physical examination is unremarkable with the excep tion of a supine blood pressure of 128/72 mm Hg and heart rate of 90 beats/min and 108/60 mm Hg and a heart rate of 115 beats/min standing. Laboratory data reveal the following: BUN = 64 mg/dL (9-25) Creatinine = 3.1 mg/dL (0.8-1.4) Glucose = 120 mg/dL (70-100) Urinalysis = Specific gravity—1,030; pH—5, 4 + glucose; 2 + protein; 2-4 red blood cells and 3-5 white blood cells; numerous hyaline and occasional granular casts In addition to the urinary findings, knowledge of the duration of the renal disease (acute vs chronic) may be diagnostically important. This can be done most accurately if previous information is available. As an example, gross hematuria following an upper respiratory infection in a patient with a previously normal urinalysis is indicative of acute disease. In comparison, a progressive rise in the plasma creatinine concentration over several years is clearly indicative of chronic renal failure. Timing may be particularly important when a hospitalized patient de velops AKI (defined as a recent elevation in the plasma creatinine concen tration; Chapter 11). In this setting, it is often possible to identify the time frame in which the injury was sustained because serial measurements of the plasma creatinine concentration are typically obtained. A rise in the plasma creatinine concentration beginning on a specific day may be due to renal in jury that occurred in the 12 to 24 hours prior to the elevated value (such as the onset of hypotension or the administration of radiocontrast media) or due to the cumulative effect of a renal toxin (such as an aminoglycoside anti biotic) or excess fluid removal with a diuretic.

CHAPTER 8 Urinalysis and Approach to the Patient With Renal Dysfunction

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