Patients with kidney disease may have a variety of different clinical presentations. Some have symptoms that are directly referable to the kidney (gross hematuria, flank pain) or to extrarenal symptoms (edema, hypertension, signs of uremia). Many patients, however, are asymptomatic and are noted on routine examination to have an elevated serum creatinine concentration or an abnormal urinalysis.
Once kidney disease is discovered, the presence or degree of kidney dysfunction and rapidity of progression are assessed, and the underlying disorder is diagnosed. Although the history and physical examination can be helpful, the most useful information is initially obtained from estimation of the glomerular filtration rate (GFR) and examination of the urinary sediment.
Estimation of the GFR is used clinically to assess the degree of kidney impairment and to follow the course of the disease. However, the GFR provides no information on the cause of the kidney disease. This is achieved by the urinalysis, measurement of urinary protein excretion, and, if necessary, radiologic studies and/or kidney biopsy.
This topic will provide an overview of the issues concerning assessment of the GFR in the patient with chronic kidney disease. The utility of the urinalysis, radiologic studies, and kidney biopsy are discussed separately, as is the general approach to the patient with kidney disease. (See "Urinalysis in the diagnosis of kidney disease" and "Radiologic assessment of renal disease" and "Indications for and complications of renal biopsy" and "Diagnostic approach to the patient with acute kidney injury (acute renal failure) or chronic kidney disease".)
OVERVIEW OF KIDNEY FUNCTION
Prior to discussing the evaluation of kidney function, it is helpful to first briefly review normal kidney physiology. The kidney performs a number of essential processes: