EVIDENCE-BASED ANSWER
YES, UNDER SOME CIRCUMSTANCES. Patients with type 2 diabetes who aren’t on insulin and perform self- monitoring of blood glucose (SMBG) show small but significant reductions in hemoglobin A1c (HbA1c) at 6 months but not at 12 months (strength of recommendation [SOR]: B, systematic reviews and meta-analyses of disease-oriented evidence).
Patients with a baseline HbA1c <8% who self-monitor don’t reduce their HbA1c levels, but patients with a baseline HbA1c >8% do (SOR: B, systematic reviews and meta-analyses of disease-oriented evidence).
More frequent SMBG—4 to 7 times weekly—doesn’t reduce HbA1c more than less frequent self-monitoring—1 or 2 times a week (SOR: B, a systematic review and meta-analysis of disease-oriented evidence).
Evidence summary
A 2012 Cochrane review and meta-analysis of 9 RCTs found that 1261 patients who used SMBG showed a small but statistically significant decrease in HbA1c at 6 months compared with 1063 controls. In 2 other RCTs, patients using SMBG showed a nonsignificant decrease in HbA1c compared with control subjects at 12 months (TABLE 1).1
TABLE 1
Difference in HbA1c by duration of self-monitoring*
| Study | Duration (months) | Total number of patients | Number of patients using SMBG | Number of patients not using SMBG | Mean HbA1c difference | 95% CI for average HbA1c reduction |
|---|---|---|---|---|---|---|
| Meta-analysis1 | 6 | 2324 | 1261 | 1063 | –0.26 | –0.39 to –0.13 Test overall effect Z=3.99 (P<.0001) |
| Meta-analysis2 | 6 | 1563 | 858 | 705 | –0.21 | –0.38 to –0.04 (P value NR) |
| Meta-analysis1 | 12 | 493 | 323 | 170 | –0.13 | –0.31 to 0.04 Test overall effect Z=1.50 (P=.13) |
| Meta-analysis2 | 12 | 648 | 391 | 257 | –0.16 | –0.38 to 0.05 (NS) |
| CI, confidence interval; HbA1c, hemoglobin A1c; NR, not reported; NS, not significant; SMBG, self-monitoring blood glucose. *Mean HbA1c was not reported for either of the 2 studies described here. | ||||||
Another meta-analysis reported similar findings. The study grouped 9 RCTs based on the duration of SMBG and examined the change in HbA1c from baseline. In 5 of the trials, SMBG for 6 months was associated with a small decrease in HbA1c, but in the other 4, SMBG for longer than one year didn’t significantly change HbA1c levels.2
Baseline values make a difference
A meta-analysis of 9 RCTs demonstrated that SMBG was marginally superior to non-SMBG for reducing HbA1c when the baseline value was >8%. SMBG didn’t lower HbA1c in patients with a baseline HbA1c <8%. The greatest change in HbA1c occurred in patients with baseline values >10% (TABLE 2).3
In another meta-analysis, 12 of 15 RCTs found SMBG to be better than non-SMBG at reducing HbA1c when the baseline was >8%.4
TABLE 2
Patients benefit from self-monitoring when baseline HbA1c is >8%
| Study | Duration (months) | Number of patients | Baseline HbA1c | Mean HbA1c difference | 95% CI for average HbA1c reduction |
|---|---|---|---|---|---|
| Meta-analysis3 | 6-12 | SMBG=301 Controls=150 | <8% | –0.15 | –0.33 to 0.03 (NS) |
| Meta-analysis4 | 6-12 | SMBG=386 Controls=390 | <8% | –0.21 | –0.37 to –0.05 (NS) |
| Meta-analysis3 | 6-12 | SMBG=964 Controls=920 | 8%-10% | –0.27 | –0.40 to –0.14 (P<.0001) |
| Meta-analysis4 | 4-12 | SMBG=1154 Controls=1156 | ≥8% | –0.38 | –0.58 to –0.18 (P value NR) |
| Meta-analysis3 | 4-7 | SMBG=29 Controls=33 | >10% | –1.23 | –2.31 to –0.14 (P<.03) |
| CI, confidence interval; HbA1c, hemoglobin A1c; NR, not reported; NS, not significant; SMBG, self-monitoring blood glucose. | |||||
Limitations of studies
Limitations of the studies (TABLES 1 AND 2) reviewed included methodological quality,1,3 limited patient compliance reporting,3 heterogeneity,1,2,4 and small sample size.2,3
More frequent self-monitoring has no effect
A systematic review of 4 RCTs with a total of 637 patients compared frequent SMBG (4-7 times a week) with less frequent self-monitoring (1-2 times a week) for periods ranging from 3 to 12 months and found no difference in reduction of values (HbA1c reduction difference between the groups = –0.21; 95% confidence interval, –0.57 to 0.15).4
Recommendations
The American Diabetes Association advocates SMBG as a guide for patients who use oral or medical nutrition therapies for diabetes. Patients should receive initial instruction in SMBG and routine follow-up evaluation of their technique and ability to use data to adjust therapy.5
The American Association of Clinical Endocrinologists (AACE) advises that SMBG can be initiated at the same time as medical therapy, lifestyle modification, specific diabetes education, or dietary consultation. If HbA1c levels are above target, the AACE recommends more frequent SMBG: preprandially, 2 hours postprandially, occasionally between 2 am and 3 am, during illness, or anytime a low glucose level is suspected.6