particle size and density, as well as adipocytokines (
CRP, IL-6, fibrinogen, adiponectin,
leptin)
shown in Table 5-2 using existing SEARCH laboratory methods. Standardized
anthropometry methods include height, weight, waist circumference; systolic and
diastolic blood pressure; and evaluation for acanthosis nigricans all follow existing
SEARCH protocols
(3, 4)
. Assessment of health behaviors all follow current SEARCH
protocols, including dietary intake by food frequency
(5)
, physical activity, alcohol, and
active and passive smoking as previously described
(6)
.
5.1.6.
Retinopathy
SEARCH will obtain retinal images using a non-mydriatic fundus camera. Consistent
with NHANES retinal photos
(7)
, two 45-degree images are taken of each eye: the first
image is centered on the optic nerve and the second centered on the macula. This device
can measure vessel anatomy which is important because retinal arteriolar and venular
calibers diameter have been associated with selected markers of atherosclerosis, stroke
and coronary heart disease in adult populations
(8, 9)
. Among adults with T2D, retinal
vessel caliber was independently associated with risk of incident nephropathy, lower
extremity amputation, and stroke mortality
(10)
. In young Australian individuals with
T1D, retinal vessel measurements were associated with duration of diabetes, gender, A1c,
blood pressure and cholesterol, and these associations were observed even among those
without DR
(11)
.
As for the SEARCH pilot effort, we will utilize the expertise of the Ocular Epidemiology
Reading Center (OERC) at the University of Wisconsin-Madison, an internationally
recognized center of excellence diabetic retinopathy research
(12)
. The OERC will grade
the images for presence and severity of DR, macular edema and retinal vessel caliber.
5.1.7.
Nephropathy
Microalbuminuria has been the mainstay of diabetic nephropathy prediction modeling.
However, recently its validity and robustness has been questioned
(13)
, with increasing
recognition of non-proteinuric diabetic kidney disease
(14, 15)
, the tendency of
microalbuminuria to regress more often than progress, and about 1/3
rd
of
microalbuminuric patients never progressing to proteinuria
(16, 17)
. Nonetheless, patients
who develop persistent microalbuminuria have about 5 times the risk of progressing to
overt nephropathy compared to those who are normoalbuminuric at a baseline
observation at least 5 years after diabetes diagnosis
(18)
. The first two phases of SEARCH
collected random urine samples. The pitfalls of random urines, especially in adolescents
who are susceptible to benign orthostatic proteinuria (frequency of 2-5%), are well
Section 5B - Data Collection (Phase 3 - 1/2011, rev. 8/2011)
Section 5B - Page 5
Cohort
Study
appreciated. However, for the SEARCH Cohorts Study, we will continue to collect a
random urine sample during the visit for longitudinal analysis. Unique to SEARCH 3,
we will add a first morning void sample that the participant will bring to the clinic.
Urinary albumin and creatinine will be measures to obtain an albumin/creatinine ratio.
Samples will not be collected during the visit on participants who are pregnant or
menstruating, have had a fever greater than 100 degrees in the past 24 hours, or who have
taken an antibiotic in the past seven days for a urinary tract infection. A dipstick test will
also be performed to test for the presence of blood or leukocytes. Urine will also be
stored (first morning void only) to assess other markers of nephropathy in the future.
(08/2011)
Serum cystatin C has been associated not only with renal function, but also positively
associated with coronary calcification among individuals with T1D
(19)
. Serum cystatin C
(20, 21)
and creatinine will be measured for calculation of estimated glomerular filtration
rate (eGFR) using the new Schwartz equation for children
(22)
. Serum creatinine will be
used to calculate eGFR in subjects over the age of 18, using the CKD EPI equation which
has been demonstrated to be more precise than the modification of Diet in Renal Disease
(MDRD) equation at higher GFRs
(23)
. eGFR will be used to monitor change in filtration
function of the kidney. All three equations will be used in those 14-18 yrs, as there has
been little investigation regarding the appropriate age or developmental stage to change
from equations traditionally used for children, to those for adults. The limited precision
of creatinine and cystatin C based estimation of GFR in the normal ranges are
recognized. However, these methods may provide useful information on changes in GFR
which are predictive of important outcomes
(24)
.
5.1.8.
Markers of Macrovascular Disease: Vascular Dysfunction
While there is great concern regarding the extent to which diabetes mellitus increases
CVD risk, very little is known about the early stages of this process as they progress in
adolescents and young adults. Vascular dysfunction occurs early in the atherosclerotic
process and it is associated, among others, with obesity, hypertension and insulin
resistance
(25)
. Since atherosclerosis is known to progress in a non-uniform fashion
throughout the vascular tree
(26)
, multiple methods have been developed to evaluate
vascular function non-invasively. Non-invasive methods to study vascular function
include, among others, assessment of arterial stiffness.
5.1.8.1.
Measurement of arterial stiffness
The SphygmoCor CPVH System from AtCor Medical (Lisle, IL) is a portable system
to measure arterial stiffness by pulse wave velocity (PWV), augmentation index (Aix)
by non-invasive arterial tonometry, and heart rate variability (HRV).
Section 5B - Data Collection (Phase 3 - 1/2011, rev. 8/2011)
Section 5B - Page 6
Cohort
Study
5.1.8.1.1.
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