Renal Pathophysiology



Diagnostic Approach AKI is traditionally divided into three broad categories: prerenal, intrinsic, and postrenal (obstruction) causes as summarized in Figure 11.1. Table 11.1 lists the most common causes for each of these categories. The approach to establishing the correct diagnosis was reviewed in Chapter 8, and the clinical characteristics of some of the individual disorders are discussed in Chapters 9 and 10. There is, however, a sequence of steps that should be followed, be ginning with the history (including timing the onset of the decline in renal function and a thorough review of medications both prescribed and over the counter), physical examination, and a careful analysis of the urine. Time of Onset In many patients with AKI, the date of onset of the decline in renal function can be identified. This is particularly true when the problem begins in the hos pital because serial routine measurements of the BUN and plasma creatinine concentration are often obtained. Suppose, for example, that the plasma cre atinine concentration began to rise on hospital day 8. In this example, some

Acute kidney injury

Postrenal (obstruction)






Interstitial nephritis




Ischemic Toxic

„ FIGURE 11.1. Main categories of acute kidney injury (AKI). Postrenal (ob structive etiologies) should be diagnosed early because the etiology and treatment are usually anatomic. About 40% to 50% of patients with AKI in the outpatient set ting have prerenal etiologies. Once intrinsic renal disease is established, about 75% to 80% of patients have ATN, ∼ 10% interstitial nephritis, and only about 5% to 10% have acute glomerulonephritis or vasculitis.

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