Clinical characteristics
Clinical and demographic data including the Charlson Comorbidity Index, using the original scoring system [18], were recorded for each patient; scores for age and severe renal failure were included in the Charlson Comorbidity Index [19]. MHD patients underwent blood and serum measurements, described in Tables 1 and 2, which were performed in the DaVita central laboratory (DeLand, Florida). Blood was obtained immediately before a routine mid-week hemodialysis. Blood test results for MHD patients presented here were values obtained monthly and averaged over the 3 months immediately prior to obtaining the other study measurements. Normal controls had blood drawn for a CBC and serum creatinine and albumin which were measured in the Harbor-UCLA Medical Center clinical laboratory. Normal volunteers who had abnormal test results were excluded from the study. Only one normal was excluded, and that was because the daily physical activity measurements from his ActiGraph (see below) were not available.
Table 1 Characteristics of study participants
Characteristic MHD patients N = 72 Normal controls N = 39  p Value
Age (years) 52.3 ± 12.9 51.0 ± 12.7 0.570
Gender (M/F) 49/23 23/16 0.391
Male (%) 68 59
DM/non-DM 23/49
Dialysis vintage (months) 53.9 ± 45.0
47.8 (51.4)
Race (%) 0.423
 African American 29 (40 %) 8 (21 %)
 Asian 22 (31 %) 19 (49 %)
 Caucasian 5 (6.9 %) 4 (10 %)
 Hispanic 15 (21 %) 8 (21 %)
 Pacific Islander 1 (1.4 %) 0
Education levels (%) 0.056
 Below high school graduate 14 (19 %) 2 (5.1 %)
 High school graduate 25 (35 %) 14 (36 %)
 ≤2 years of college
 ≥2 years of college 33 (46 %) 23 (59 %)
Charlson comorbidity index 5.7 ± 2.7 –
Weight (kg) 78.9 ± 21.5 74.8 ± 14.5 0.237
76.4 (25.6) 77.0 (18.9)
Body mass index (kg/m2) 27.8 ± 5.8 27.0 ± 3.9 0.388
26.2 (7.6) 27.0 (5.9)
Lean body mass (kg) 54.0 ± 15.4 51.4 ± 11.3 0.315
51.5 (17.7) 49.1 (15.9)
Lean body mass index (kg/m2) 18.9 ± 3.4 18.4 ± 2.7 0.472
18.3 (3.0) 18.2 (3.2)
Body fat (%) 28.3 ± 8.5 27.9 ± 8.1 0.786
26.8 (11) 25.8 (14)
Serum albumin (g/dL) 4.1 ± 0.3 4.1 ± 0.2 0.606
Serum creatinine (mg/dL) 10.5 ± 4.3 0.84 ± 0.2 <0.0001
9.8 (3.8)
nPNA (g protein/kg/day) 1.10 ± 0.26
Sp Kt/Vurea 1.72 ± 0.40
Serum TIBC (ug/mL) 240.6 ± 40.1
Serum ferritin (ng/mL) 453.2 ± 313.2
Hemoglobin (g/dL) 11.2 ± 0.8 13.8 ± 1.3 <0.0001
11.2 (0.9) 14 (2.1)
Serum calcium (mg/dL) 9.0 ± 0.7
Serum phosphorus (mg/dL) 5.3 ± 1.4
Serum PTH (pg/mL) 480 ± 277
456 (305)
Serum bicarbonate (mEq/L) 24.5 ± 2.6
Data expressed as mean ± standard deviation. Non-normally distributed data are expressed as median values with the interquartile range (IQR, i.e., the arithmetic difference between the 25th percentile value and the 75th percentile value) shown in parentheses
nPNA normalized protein nitrogen appearance, also referred to as protein catabolic rate; TIBC total iron binding capacity; PTH parathyroid hormone
Table 2 Physical activity and physical performance; MHD patients vs. normal controls
MHD patients N = 72 Normal controls N = 39  p Value
Human activity profile
 Maximum activity score 82.5 (13.5) 92 (5) <0.0001
 Adjusted activity score 72 (22) 89 (5) <0.0001
Time spent by monitor readings (%)
 Sleep or marked physical inactivity 81.9 ± 5.8 72.8 ± 6.0 <0.0001
 Light activity 14.4 ± 4.4 20.0 ± 4.5 <0.0001
 ≥ Moderate activity 3.7 ± 2.1 7.2 ± 3.0 <0.0001
Average daily physical activity (vector magnitude)
 Daily physical activity (mean of 7 days) 395,727 (222,350) 636,112 (243,634) <0.0001
 Day of HD 327,250 (188,085)
 1-day-post-HD 442,720 (246,824)a
 2-days-post HD 393,353 (275,123)b
6-min walk distance (meters) 441.3 ± 121.9 617.6 ± 63.2 <0.0001
Sit-to-stand test (no. cycles in 30 s) 15.9 ± 5.3 26.2 ± 5.4 <0.0001
Stair-climbing test (seconds per 22 stairs) 15.8 ± 11.0 9.8 ± 1.1 <0.0001
Data expressed as mean ± standard deviation. Non-normally distributed data are expressed as median values with the interquartile range (IQR, i.e., the arithmetic difference between the 25th percentile value and the 75th percentile value) shown in parentheses
a1-day-post-HD vs day of HD p = 0.018
b2-days-post-HD vs day of HD p = 0.057; 1-day-post-HD vs 2-days-post-HD p = 0.441