General Considerations
A patient with renal disease can present either as an initial
outpatient or inpatient consultation. Some patients may be
referred because of abnormal urinary fi ndings, such as hematuria
or proteinuria, which may have been incidentally
discovered during routine clinical evaluation or as part of
initial employment requirements. Depending on the stage of
renal disease, they can present with mild edema or generalized
pruritus, as well as more advanced signs and symptoms
of uremia, such as decreased appetite, weight loss, and even
alterations in mental status. In general, the symptoms and
signs of patients with renal disease tend to be nonspecifi c
(Table 1–1). Still others would present only with elevation in
serum creatinine.
To narrow the differential diagnosis, it is necessary to fi rst
determine whether the disease is acute, subacute, or chronic
on presentation. However, there is usually an overlap in these
stages, and at times, it is not exactly clear. Certainly, a patient
who presents with an elevated serum creatinine that was
documented to be normal a few days previously has an acute
presentation, whereas a patient who presents with a previously
elevated serum creatinine that has been rising steadily
over the past several months to years has a chronic disease.
Oftentimes, acute exacerbations of chronic renal disease are
common presentations.
The next question concerns which segment or component
of the renal anatomy is involved. This is subdivided into
prerenal, postrenal, or renal (Table 1–2).
Prerenal disease refers to any process that decreases renal
perfusion, such as intravascular volume depletion, hypotension,
massive blood loss, or third spacing of fl uids. It can also
be due to congestive heart failure, whereby decreased effective
circulating volume decreases blood fl ow toward the kidneys
(see Chapter 9).
Postrenal disease refers to any obstruction that impedes
urinary fl ow through the urinary tract. Examples include
benign prostatic hypertrophy or cervical malignancy (see
Chapter 16).
Renal involvement is further subdivided into vascular,
glomerular (see Chapters 23–35), or tubulointerstitial disease
(see Chapters 36 and 37), depending on which segment
is involved.
 Assessment of Glomerular
Filtration Rate (GFR)
The most common method of assessing renal function is
by estimation of the glomerular fi ltration rate (GFR). The
GFR gives an approximation of the degree of renal function.
Daily GFR in normal subjects is in the range of 150–250
L/24 hours or 100–120 mL/minute/1.73 m2 of body surface
area. GFR is decreased in those with renal dysfunction,
and is used to monitor renal function in those with
chronic kidney disease. It is also used to determine the appropriate
timing for initiation of renal replacement therapy.
To date, there are several methods by which GFR is
measured, namely serum creatinine concentration, 24-hour
creatinine clearance, as well as estimation equations such as
the Cockroft–Gault formula and the Modifi cation of Diet in
Renal Disease (MDRD) Study formula (Table 1–3).
Using the serum creatinine alone to estimate renal
functioning is inaccurate for several reasons. First, a small
amount of creatinine is normally secreted by the tubules,
and this amount tends to increase as progressive renal decline
occurs, thereby overestimating the true GFR value.
Similarly, there are factors that increase serum creatinine
without truly affecting renal function, such as dietary meat
(protein) intake, volume of muscle mass, and medications
that interfere with tubular secretion of creatinine such as
cimetidine, trimethoprim, and probenecid. Elderly patients,
those with cachexia, amputees, as well as patients
with spinal cord injury or disease tend to have less muscle
mass, hence, lower serum creatinine values (Table 1–4).