michigan hypertension core curriculum - State of Michigan

to assess renal dimensions and duplex to assess renal resistive index [RRI]), and selective renal
arteriography in some patients (to assess cortical blood flow and intrarenal arteriolar patterns).
Individually, none of these parameters is an absolute predictor of outcome, and over-reliance on any
single test may exclude patients who might benefit from revascularization. 32-34 In any given patient,
certain measures may indicate greater degrees of nephropathy than others, but advanced nephropathy
is characterized by proteinuria > 1 gram/24 hr, renal length < 10 cm, and RRI >0.8, compared to others
with less nephropathy.
Scr is the most common measure of renal function, but is limited for assessing the extent of
dysfunction or for distinguishing nephropathy from renal ischemia. Scr is insensitive to glomerular
filtration rate (GFR) until 50-75 % of renal mass has been lost (Figure 7). Stated in another way, a
patient who loses 50 % of renal mass (as might occur after nephrectomy or with unilateral renal artery
occlusion) should have a normal Scr; Scr > 2 mg/dL in a patient with unilateral ARAS is generally
indicative of significant nephropathy. 35 Selective renal arteriography and renal biopsy can be used
to assess nephropathy. Although a biopsy can reliably confirm nephropathy, it is impractical and
uncommonly used. Arteriographic findings provide useful information that complements the noninvasive
evaluation (Table 4, Figure 5).
Clinical evaluation of renal ischemia. Several noninvasive and invasive methods have utility for
estimating renal blood flow, assessing the hemodynamic significance of RAS, and identifying renal
ischemia (Table 6). 36,37 Nuclear scintigraphy with Technetium-labeled pentetic acid ( 99M Tc-DTPA) is
reliable for measuring fractional renal blood flow 36-39 and when used in conjunction with 125 I-Iothalamate,
allows accurate measurement of total- and single kidney-GFR. In patients with unilateral RAS,
hypoperfusion of the stenotic kidney is reasonable evidence for renal ischemia 36 ; patients with normal
renal blood flow may have RAS, but not ischemia.
The invasive evaluation of renal ischemia is based on hemodynamic assessment of RAS
rather than renal artery perfusion per se (Table 6). Stenosis severity is determined by visual estimates
or quantitative angiography using a single angiographic projection may be inaccurate due to plaque
eccentricity and vessel foreshortening, and has poor correlation with hemodynamic significance. 40
Translesional pressure gradients (TLG) can be measured with small catheters or special pressure
wires, and TLG > 20 mmHg is considered hemodynamically significant. 20 Fractional flow reserve (FFR)
can determine the hemodynamic significance of RAS 40,41 , and FFR < 0.80 may predict a favorable BP
110 Hypertension Core Curriculum