7. HbA1c ‐ Studies undertaking multivariable regression analyses to determine the effect of HbA1c on progression to PDR.
| Study | Study type | Time years | N at baseline | Adjustment factors | Effect estimate | P value | Comments | ||
| Type | Value | 95% CI | |||||||
| Type 1 diabetes | |||||||||
| Lloyd 1995 | Prospective cohort | 2 | 496 | DM duration, DR severity at baseline | RR | 5.75 | 1.54 to 21.4 | Top quartile compared to other three quartiles | |
| Klein 1984 | Prospective cohort | 4 | 996 | DM duration, DR severity at baseline, age, sex | RR | 1.5 | 1.4 to 1.8 | < 0.0001 | Per 1 % increase |
| Janghorbani 2000 | Retrospective cohort | 5 | 1349 | DM duration, SBP | RR | 1.83 | 1.4 to 2.39 | ≥ 11 relative to < 11% | |
| Roy 2006 | Prospective cohort | 6 | 725 | Age, hypertension, proteinuria | OR | 1.32 | 1.22 to 1.43 | < 0.001 | Per 1 % increase |
| Porta 2001 | Prospective cohort | 7 | 2013 | DM duration, DR severity at baseline, age DM diagnosis, SBP, albumin excretion rate, waist‐to‐height | Regression estimate | 3.03 | 2.49 to 3.69 | 0.0001 | Comparator unclear |
| Arfken 1998 | Retrospective cohort | 7 | 312 | DR severity at baseline, race, follow‐up period | OR | 1.92 | 1.36‐ to 2.7 | 0.0002 | Per 2 % increase |
| Kullberg 1993 | Prospective cohort | 8 | 172 | DM duration, age DM diagnosis, sex, hypertension | Described narratively, data not reported. | ||||
|
WESDR Klein 1994 |
Prospective cohort | 10 | 334 | DM duration, DR severity at baseline, age, sex | OR | 1.9 | 1.7 to 2.2 | < 0.0001 | Per 1 % increase |
| WESDR Klein XVII |
Prospective cohort | 14 | 996 | DR severity at baseline, hypertension, smoking, aspirin | OR | 1.81 | 1.6 to 2.05 | < 0.001 | Per 1 % increase |
| Skrivarhaug 2006 | Prospective cohort | 24 | 368 | DM duration, DR severity at baseline, age, age at DM diagnosis, hypertension, cholesterol, albumin excretion rate, smoking | RR | 2.05 | 1.44 to 2.93 | < 0.001 | Unclear |
|
WESDR Klein XXII |
Prospective cohort | 24 | 955 | SBP, proteinuria, BMI | HR | 1.38 | 1.31 to 1.46 | < 0.001 | Per 1 % increase |
| Type 2 diabetes | |||||||||
|
WESDR Klein 1988 |
Prospective cohort | 4 | 1370 | DM duration, DR severity at baseline, age, sex | OR | 1.30 | 1.00 to 1.60 | < 0.05 | Older‐onset taking insulin Per 1 % increase |
| Cho 2019 | Retrospective cohort | 4 | 1527 | Age, estimated glomerular filtration rate | OR | 1.11 | 0.93 to 1.32 | Nonsignificant | Per 1 % increase |
| Kim 1998 | Prospective cohort | 5 | 228 | DM duration, age, albumin excretion rate, BMI | RR | 1.30 | 1.04 to 1.61 | < 0.05 | Mean HbA1c during follow‐up |
| Gange 2021 | Retrospective cohort (electronic database) | 5 | 71815 | Age DM diagnosis, race, BMI, smoking, socioeconomic status, insulin use, comorbidities | OR | 2.10 | 1.64 to 2.69 | < 0.001 | Maximum > 9% vs < 6.5% |
| Okudaira 2000 | Prospective cohort | 6 | 527 | DBP | HR | 1.43 | 1.23 to 1.67 | 0.00001 | Mean HbA1c |
| Lee 2021 | Retrospective cohort | 6 | 2623 | DR severity at baseline, age, sex, BMI | HR | 1.09 | 0.97 to 1.22 | 0.164 | Per one standard deviation |
| Kim 2014 | Retrospective | 6 | 452 | DM duration, BMI | HR | 1.19 | 1.10 to 1.46 | 0.005 | Per unit increase |
|
WESDR Klein 94 |
Prospective cohort | 10 | 1370 | DM duration, DR severity at baseline | OR | 1.2a 1.9b |
1.00 to 1.50 1.50 to 2.50 |
0.07 < 0.0001 |
Per 1 % increase |
| Kalter‐Leibovici 1991 | Prospective cohort | 10 | 330 | DM duration, socioeconomic | OR | 1.9 | 1.4 to 2.5 | 10‐year HbA1c | |
| Type 1 and type 2 diabetes | |||||||||
| Harris 2013 | Retrospective cohort (electronic database) | 5 | 4617 | Age, sex, race, comorbidities | HR | 1.14 | 1.07 to 1.21 | < 0.05 | With increasing HbA1c |
| Janghorbani 2000 | Retrospective cohort | 5 | 3482 | DM duration, SBP | RR | 1.33 | 1.13 to 1.53 | ≥ 11 | |
BMI: body mass index; CI: confidence interval; DBP: diastolic blood pressure; DM: diabetes mellitus; DR: diabetic retinopathy; HbA1c: glycated haemoglobin/haemoglobin A1c; HR: hazard ratio; NPDR: non‐proliferative diabetic retinopathy; OR: odds ratio; PDR: proliferative diabetic retinopathy; RR: risk ratio; SBP: systolic blood pressure; vs: versus