Stepwise Approach To Diagnosis Of Acute Renal Failure

Step 1

Step 2

Step 3

Step 4

History

Consider urinary diagnostic

Consider selected

Consider renal biopsy

Record review

indices (see Fig. 12-16)

therapeutic trials

Consider empiric therapy

Physical examination

Consider need for further

for suspected diagnosis

Urinary bladder catherization

(if oligoanuric) Urinalysis (see Fig. 12-15)

evaluation to exclude urinary tract obstruction Consider need for more data to assess intravascular volume or cardiac output status Consider need for additional blood tests Consider need for evaluation of renal vascular status

Stepwise approach to diagnosis of acute renal failure (ARF). The multiple causes, predisposing factors, and clinical settings demand a logical, sequential approach to each case of ARF. This figure presents a four-step approach to assessing ARF patients in an effort to delineate the cause in a timely and cost-effective manner. Step 1 involves a focused history, record review, and examination. The salient features of these analyses are noted in more detail in Figure 12-13. In many cases, a single bladder catheterization is needed to assess the degree of residual volume, which should be less than 30 to 50 mL. Urinalysis is a critical part of the initial evaluation of all patients with ARF. Generally, a relatively normal urinalysis suggests either a prerenal or postrenal cause, whereas a urinalysis containing cells and casts is most compatible with a renal cause. A detailed schema of urinalysis interpretation in the setting of ARF is depicted in Figure 12-15. Usually, after Step 1 the clinician has a reasonably good idea of the likely cause of the ARF. Sometimes, the information noted under Step 2 is needed to ascertain definitively the cause of the ARF. More details of Step 2 are depicted in Figure 12-14. Oftentimes, urinary diagnostic indices (see Fig. 12-16), are helpful in differentiating between prere-nal (intact tubular function) and acute tubular necrosis (impaired tubular function) as the cause of renal failure. Sometimes, further evaluation (usually ultrasonography, less commonly computed tomography or magnetic resonance imaging) is needed to exclude the possibility of bilateral ureteric obstruction (or single ureteric obstruction in patients with a single kidney). Occasionally, additional studies such as central venous pressure or left ventricular filling pressure determinations are needed to better assess whether prerenal factors are contributing to the ARF. When the cause of the ARF continues to be difficult to ascertain and renal vascular disorders (see Fig. 12-17 and 12-18), glomerulonephritis (see Fig. 12-19) or acute interstitial nephritis (see Fig. 12-20) remain possibilities, additional blood analyses and other tests described in Figures 12-18 through 12-20 may be indicated. Sometimes, selected therapeutic trials (eg, volume expansion, maneuvers to increase cardiac index, ureteric stent or nephrostomy tube relief of obstruction) are necessary to document the cause of ARF definitively. Empiric therapy (eg, corticosteroids for suspected acute allergic interstitial nephritis) is given as both a diagnostic and a therapeutic maneuver in selected cases. Rarely, despite all efforts, the cause of the ARF remains unknown and renal biopsy is necessary to establish a definitive diagnosis.

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