Table 1.
Selected characteristics of included studies
| No. of studies by study designs | |||
|---|---|---|---|
| All | Without follow-up | With follow-up | |
| N | 286 | 245 | 41 |
| Peripheral immune biomarkers as primary exposure of interest, n (%) | |||
| Yes | 258 (90.2) | 224 (91.4) | 34 (82.9) |
| No | 28 (9.8) | 21 (8.6) | 7 (17.1) |
| Publication period, n (%) | |||
| 1980s and before | 8 (2.8) | 8 (3.3) | 0 (0.0) |
| 1990–1999 | 31 (10.8) | 31 (12.7) | 0 (0.0) |
| 2000–2009 | 81 (28.3) | 72 (29.4) | 9 (22.0) |
| 2010–2019 | 117 (40.9) | 102 (41.6) | 15 (36.6) |
| 2020 and after | 49 (17.1) | 32 (13.1) | 17 (41.5) |
| Sampling representativeness, n (%) | |||
| Single-hospital | 214 (74.8) | 206 (84.1) | 8 (19.5) |
| Multi-hospital | 34 (11.9) | 28 (11.4) | 6 (14.6) |
| Regional | 33 (11.5) | 8 (3.3) | 25 (61.0) |
| National | 5 (1.7) | 3 (1.2) | 2 (4.9) |
| Study population by region, n (%) | |||
| Asia | 53 (18.5) | 47 (19.2) | 6 (14.6) |
| Europe | 152 (53.1) | 135 (55.1) | 17 (41.5) |
| North America | 54 (18.9) | 38 (15.5) | 16 (39.0) |
| Others * | 27 (9.4) | 25 (10.2) | 2 (4.9) |
| Total sample size, n (%) | |||
| 20–99 | 158 (55.2) | 152 (62.0) | 6 (14.6) |
| 100–999 | 107 (37.4) | 90 (36.7) | 17 (41.5) |
| 1000 and over | 21 (7.3) | 3 (1.2) | 18 (43.9) |
| AD assessment # , n (%) | |||
| NINCDS-ADRDA | 207 (72.4) | 186 (75.9) | 21 (51.2) |
| DSM-III or IV | 89 (31.1) | 76 (31.0) | 13 (31.7) |
| ICD-9 or 10 | 11 (3.8) | 3 (1.2) | 8 (19.5) |
| Others | 25 (8.7) | 21 (8.6) | 4 (9.8) |
| Not reported | 25 (8.7) | 21 (8.6) | 4 (9.8) |
| AD severity examined, n (%) | |||
| Yes | 42 (14.7) | 40 (16.3) | 2 (4.9) |
| No | 244 (85.3) | 205 (83.7) | 39 (95.1) |
| Biomarker sample source, n (%) | |||
| Serum | 121 (42.3) | 108 (44.1) | 13 (31.7) |
| Plasma | 113 (39.5) | 101 (41.2) | 12 (29.3) |
| Serum and plasma | 46 (16.1) | 32 (13.1) | 14 (34.1) |
| Not reported | 6 (2.1) | 4 (1.6) | 2 (4.9) |
| Assay type reported, n (%) | |||
| Yes | 272 (95.1) | 238 (97.1) | 34 (82.9) |
| No | 14 (4.9) | 7 (2.9) | 7 (17.1) |
| Mean age of AD cases, n (%) | |||
| Middle-aged (<65 years) | 12 (4.2) | 10 (4.1) | 2 (4.9) |
| Youngest-old (65–74 years) | 112 (39.2) | 103 (42.0) | 9 (22.0) |
| Middle-old (75–84 years) | 117 (40.9) | 106 (43.3) | 11 (26.8) |
| Oldest-old (85 years) | 2 (0.7) | 2 (0.8) | 0 (0.0) |
| Not reported | 43 (15.0) | 24 (9.8) | 19 (46.3) |
| Other sociodemographic characteristics examined, n (%) | |||
| Gender | 236 (82.5) | 205 (83.7) | 31 (75.6) |
| Education | 93 (32.5) | 68 (27.8) | 25 (61.0) |
| Race/ethnicity | 31 (10.8) | 22 (9.0) | 9 (22.0) |
| None reported | 39 (13.6) | 35 (14.3) | 4 (9.8) |
*
Others include Africa, Australia, and South America
#
Some studies used more than one AD assessment tool