This supplement provides detailed protocols of the measurements performed within
The Maastricht Study.
Laboratory assessments. Plasma glucose is measured with a standard enzymatic
hexokinase reference method, and serum total cholesterol, HDL cholesterol,
triglycerides, albumin and serum and urine creatinine and uric acid levels are
measured with standard (enzymatic and/or colorimetric) methods by an automatic
analyzer (Beckman Synchron LX20, Beckman Coulter Inc., Brea, USA). When
appropriate LDL cholesterol is calculated according to the Friedewald formula [31].
Measurement of creatinine is based on the Jaffé method traceable to isotope dilution
mass spectrometry (Synchron LX20, Beckman Coulter Inc., Brea, USA). HbA1c is
measured with ion-exchange high performance liquid chromatography (HPLC)
(Variant tm II, Bio-Rad, Hercules, California, USA). Plasma hemoglobin, hematocrit,
red blood cell, leukocyte and platelet count and mean platelet volume are measured
by an automated hematology system (Sysmex XE5000, Kobe, Japan). Urinary
albumin is measured with a immunoturbidimetric assay (Cobas c systems, Roche
diagnostics, Mannheim, Germany).
Physical examination. Weight and height are measured without shoes and wearing
light clothing using a scale and stadiometer to the nearest 0.5 kg or 0.1 cm (Seca,
Hamburg, Germany). Circumference measures of the waist, hip, mid-upper arm, calf
and wrist are measured with a flexible plastic tape measure (Seca, Hamburg,
Germany). Waist and hip circumference are measured in duplicate midway between
the lower rib margin and the iliac crest at the end of expiration, and at the level of the
widest circumference over the greater trochanter, both to the nearest 0.5 cm. Midupper arm circumference is measured in duplicate at the dominant arm at the midpoint between the tip of the shoulder and the tip of the elbow to the nearest 0.1 cm.
Calf circumference is measured in duplicate at the dominant leg while the participant
is sitting at the level of the widest circumference of the calf to the nearest 0.1 cm.
Wrist circumference is measured in duplicate at the dominant arm to the nearest 0.1
cm. Biceps, triceps, suprailiac and subscapular skinfolds are measured three times at
the dominant side of the body to the nearest 0.1 mm by use of a Harpenden skinfold
caliper (Harpenden, West Sussex, UK).
Physical function and performance. A 6-minute fast walk test is conducted to assess
general physical function. Subjects were instructed to walk from one end to the other
of a 20 meter hallway as fast as possible, while attempting to cover as much ground
as possible in the allotted 6 minutes. Technicians encouraged subjects with the
standardized statements “You're doing well” or “Keep up the good work,” but were
asked not to use other phrases. Subjects were allowed to stop and rest during the
test, but were instructed to resume walking as soon as they felt able to do so.
Blood pressure. Office blood pressure is determined three times on the right arm
after a 10-minute rest period, using a non-invasive blood pressure monitor (Omron
705IT, Japan). When the difference between measurement two and three is more
than 10mmHg, a fourth measurement is performed. All available measurements are
used to calculate the average blood pressure. Ambulatory 24-h blood pressure and
7-days home blood pressure (WatchBP O3 and WatchBP home, Microlife,
Switzerland, respectively) are measured at the non-dominant arm. 24-h blood
pressure is measured using an ambulatory device that is programmed to take blood
pressure readings every 15 minutes from 8.00 – 23.00 and every 30 minutes from
23.00 – 8.00. Finally, participants are requested to measure blood pressure at home
for 7 days using an ambulatory monitor. Home blood pressure is measured twice
around 8.00 before breakfast and 20.00 after dinner after 5 minutes of seated rest,
during 7 consecutive days.
Fundus photography. To determine the presence of diabetic retinopathy, fundus
photography of both eyes is performed. All fundus photographs are performed with a
non-mydriatic auto fundus camera (Model AFC-230, Nidek, Gamagori, Japan) in 45
degrees of at least three fields: field 1 is centered on the optic disc (1M), field 2 is
centered on the macula (2M) and field 3 is positioned one disc-diameter temporal to
the center of the macula (3M).