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| Official reprint from UpToDate®  | |

Diagnostic approach to the patient with acute or chronic kidney disease |
Theodore W Post, MD
Burton D Rose, MD | Section Editor 
Gary C Curhan, MD, ScD | Deputy Editor 
Alice M Sheridan, MD |
Last literature review for version 17.2: May 1, 2009  |  This topic last updated: April 30, 2009  |INTRODUCTION — Patients with renal disease may have a variety of different clinical presentations. Some have symptoms (or signs) that are directly referable to the kidney (hematuria, flank pain) or to associated extrarenal symptoms (edema, hypertension, signs of uremia). Many patients, however, are asymptomatic and are noted on routine examination to have an elevated plasma creatinine concentration or an abnormalurinalysis (such as microscopic hematuria or proteinuria). Specific disorders are more likely to be either acute or chronic in duration, thereby narrowing the differential diagnosis among patients presenting with similar clinical findings related to the kidney.
An overview of the diagnostic approach to the patient with renal disease is presented in this topic. There are two major components to thisevaluation:
* Assessment of renal function by estimation of the glomerular filtration rate (GFR), initially by measurement of the plasma creatinine concentration and (in those with stable renal function) the application of formulas which provide reasonable, but not precise, estimates of GFR. (See "Assessment of kidney function: Serum creatinine; BUN; and GFR").
* Careful examination of theurine (by both qualitative chemical tests and microscopic examination), since the urinary findings narrow the differential (show table 1). (See "Urinalysis in the diagnosis of renal disease").
The epidemiology of chronic kidney disease and recommendations for screening are presented separately. (See "Epidemiology of chronic kidney disease and screening recommendations").
MAJOR CAUSES OF KIDNEYDISEASE — The causes of acute or chronic kidney disease are traditionally classified by that portion of the renal anatomy most affected by the disorder [1]. Renal function is based upon four sequential steps, which are isolated to specific areas of the kidney or surrounding structures:
* First, blood from the renal arteries and their subdivisions is delivered to the glomeruli.
* The glomeruliform an ultrafiltrate, nearly free of protein and blood elements, which subsequently flows into the renal tubules.
* The tubules reabsorb and secrete solute and/or water from the ultrafiltrate.
* The final tubular fluid, the urine, leaves the kidney, draining sequentially into the renal pelvis, ureter, and bladder, from which it is excreted through the urethra.
Renal disease can becaused by any process that interferes with any of these structures and/or functions. Identifying prerenal (reduced renal perfusion) and postrenal (obstructive) diseases is particularly important because they may be readily reversible.
There is also a variable time course. The distinction between acute, subacute and chronic kidney disease is arbitrary. Clearly, a rise in the plasma creatinineconcentration or an abnormality on the urinalysis that has developed within days to weeks represents an acute process, whereas evidence of renal disease extending for months to years is a chronic process that may be associated with acute exacerbations.
Prerenal disease — The two major causes of reduced renal perfusion are volume depletion and/or relative hypotension. This may result from truehypoperfusion due to bleeding, gastrointestinal, urinary, or cutaneous losses, or to effective volume depletion in heart failure, shock, or cirrhosis. (See "Chapter 8A: Effective circulating volume and the steady state").
Prerenal disease is most commonly associated with an acute time course. However, among patients with chronic kidney disease, the addition of a prerenal process may result in acute...
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