Adherence of self-monitoring of blood glucose in persons with type 1 diabetes in Sweden

Abstract

Background

In persons with type 1 diabetes, obtaining good glycemic control is crucial in avoiding microvascular and macrovascular complications from the eyes, kidneys, nerves, and cardiovascular system, and reducing excess mortality.^1–3 Simultaneously, it is important to minimize the risk of hypoglycemia, which leads to considerable discomfort and risk of serious complications for many patients.² Previous studies have shown a correlation between frequent self-monitoring of blood glucose (SMBG) and glycemic control measured by hemoglobin A1c (HbA1c).^4–9 The difference in HbA1c between those not measuring their blood glucose at all and those measuring only a few times every week, but not daily, has been shown to be negligible.^{5 6} In comparison, the difference between those never or seldom measuring and those measuring 3–4 times per day is about 1% (10 mmol/mol). The difference between measuring 3–4 times per day and measuring 10 times per day has also been shown to have an effect on HbA1c of about 1% (10 mmol/mol).⁷

The American Diabetes Association's (ADA) Standards of Medical Care in Diabetes, suggest a partly individualized number of SMBG measurements per day for patients on intensive insulin regimes (multiple daily insulin injections or insulin pump). SMBG is recommended at least 4 times per day, but for many patients 6–10 times per day is appropriate to achieve good metabolic control.^{10 11} Earlier studies on patients with diabetes type 1 have shown varying adherence to guidelines, from two-thirds of patients not performing daily SMBG,⁶ to 85% of patients measuring 3 times per day or more.⁷ Some studies are limited to patients downloading blood glucose meter data at the clinic, probably leaving out a large proportion of non-adherent patients. Many modern studies are focused on continuous glucose monitoring (CGM); however, a vast majority of patients are limited to traditional blood glucose meters because of limited reimbursement of CGM. Therefore, more recent data on patient adherence to modern guidelines using traditional blood glucose meters is weak, especially in Sweden, where no such study has been conducted.

The aim of the present study was to describe the proportion of patients measuring blood glucose levels at least 4 times per day. Secondary objectives were to further investigate possible predictors for good SMBG adherence as well as studying the association between SMBG frequency and HbA1c.

Methods

Results

SMBG according to guidelines

The proportion of subjects with SMBG ≥4 daily in the last 30 days was 43.9% (n=138 of 314, 95% CI 38.5% to 49.4%). For the three clinics with highest response rate, 41.3% performed ≥4 SMBG/day (n=90 of 218, 95% CI 34.7% to 47.8%) (table 2). SMBG for individuals within the same clinics were essentially independent (r<0.05) and a sensitivity analysis accounting for within-clinic correlation gave similar results to those presented in table 2 (data not shown). The distribution of SMBG frequency is shown for each group in figure 1A.

Table 2

Primary Analysis: Self-Monitoring of Blood Glucose.

	Site 1–3 (n=228)	All sites (n=329)
Responders on SMBG last 30 days	n=218	n=314
SMBG >= 4 last 30 days	90 (41.3%) (34.7% to 47.8%)	138 (43.9%) (38.5% to 49.4%)
SMBG >= 3 last 30 days	124 (56.9%) (50.3% to 63.5%)	184 (58.6%) (53.2% to 64.0%)
SMBG <= 1 last 30 days	42 (19.3%) (14.0% to 24.5%)	56 (17.8%) (13.6% to 22.1%)
Responders on SMBG last 7 days	n=223	n=323
SMBG >= 4 last 7 days	93 (41.7%) (35.2% to 48.2%)	147 (45.5%) (40.1% to 50.9%)
SMBG >= 3 last 7 days	138 (61.9%) (55.5% to 68.3%)	202 (62.5%) (57.3% to 67.8%)
SMBG <= 1 last 7 days	35 (15.7%) (10.9% to 20.5%)	47 (14.6%) (10.7% to 18.4%)
Number of daily SMBG last 30 days	3.5 (2.4) 3.2 (0.0; 14.7) n=218	3.7 (2.7) 3.3 (0.0; 14.7) n=314
Number of daily SMBG last 7 days	3.6 (2.2) 3.6 (0.0; 10.6) n=223	3.9 (2.5) 3.6 (0.0; 12.9) n=323
Number of SMBG per day as estimated by study persons	3.9 (2.6) 4 (0; 25) n=207	4.2 (2.7) 4 (0; 25) n=307
How many SMBG per day do you think is recommended?	3.9 (1.1) 4 (1; 5) n=171	3.9 (1.1) 4 (1; 5) n=246
Number of postprandial measurements per week	6.3 (7.7) 4 (0; 35) n=195	7.3 (8.9) 4 (0; 50) n=290
Number of complete blood sugar curves per month	2.3 (6.8) 0.0 (0; 31) n=190	3.2 (8.2) 0 (0; 31) n=275

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Results are presented for the sites with ≥70% response rate separately and for all five sites.

For categorical variables, n (%) / 95% CI for proportion is presented. Confidence intervals are computed using normal approximation.

Mean (SD) / median (min; max) / n = is presented for continuous variables.

SMBG, self-monitoring of blood glucose.

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Figure 1

(A) Distribution of number of daily SMBG last 30 days. (B) HbA1c as function of daily SMBG. HbA1c, hemoglobin A1c; SMBG, self-monitoring of blood glucose.

The median patient belief was that recommended number of daily SMBG was 4. 29.7% of patients believed that ≤3 SMBG measurements per day were recommended by healthcare providers, and 11.4% believed that ≤2 SMBG measurements were recommended (see online table S2 supplement). Postprandial measurements were seldom performed; the median number per week was 4 in both groups.

supplementary data

bmjdrc-2016-000342suppl.pdf

The number of SMBG measurements performed during the last 30 days correlated with patient perceptions of the mean number of measurements performed per day, r=0.89 (p<0.0001) in all clinics. Patient apprehension of the recommended number of SMBG measurements showed a weaker yet statistically significant correlation to the actual number of measurements, r=0.42, p<0.0001.

Using data from all clinics, predictors for performing more frequent SMBG were older age (p=0.033) and female sex (p<0.001), using multiple regression analysis (R²: 3.6%). In univariate analyses, residential status (living single with children) and high physical activity showed a significant association with SMBG frequency (p=0.046 and p=0.049, respectively). The association with high stress level was of borderline significance (p=0.055). When using the same methodology for the three clinics where response rate was ≥70%, age was the only significant predictor (p=0.004). Results are shown in table 3. When using a model that accounted for dependencies within clinics, a non-significant intraclinic correlation was seen and similar results in the analysis of predictors of more frequent SMBG were obtained (data not shown).

Table 3

Average daily SMBG last 30 days related to patient characteristics (all sites)

	Univariable*		Multivariable†
Variable	Beta (95% CI)	p-Value	Beta (95% CI)	p-Value
Age (per 5 years)	0.10 (0.01 to 0.19)	0.029	0.10 (0.01 to 0.18)	0.033
Female sex	0.80 (0.21 to 1.39)	0.0084	0.78 (0.19 to 1.37)	0.0097
Diabetes duration (per 5 years)	−0.00 (–0.10 to 0.10)	0.99
Smoker	−0.17 (–0.97 to 0.63)	0.68
High school or higher	0.09 (–0.82 to 0.99)	0.85
Occupation
Working/Student	−0.53 (–1.18 to 0.12)	0.11
Retired	0.54 (–0.20 to 1.27)	0.15
Unemployed/Sick-leave/Disability pension	0.26 (–0.72 to 1.25)	0.60
Residential status
Living with other adult(s)	0.56 (–0.15 to 1.27)	0.12
Single with children	−1.31 (–2.60 to -0.02)	0.046
Living alone	−0.20 (–0.99 to 0.60)	0.63
Stress level (1-5)	0.27 (–0.01 to 0.55)	0.059
Physical activity (1-4)	0.32 (0.00 to 0.64)	0.049
BMI (per 5 units)	0.00 (–0.37 to 0.37)	0.99
Insulin pump	0.12 (–0.58 to 0.82)	0.73
Carbohydrate counting	0.34 (–0.31 to 0.98)	0.31
Laser treatment	−0.11 (–0.85 to 0.62)	0.76
Microalbuminuria	0.07 (–1.47 to 1.62)	0.93
Foot ulcer	−0.77 (–2.12 to 0.57)	0.26
Stroke	0.47 (–1.07 to 2.02)	0.55
Myocardial infaction	0.49 (–1.38 to 2.37)	0.61
Percutaneous coronary intervention	−0.31 (–1.90 to 1.27)	0.70
Aorto-coronary bypass surgery	0.11 (–1.87 to 2.08)	0.92

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* All tests are performed with univariable linear regression.

† Multivariable linear regression model found by stepwise selection. R-squared for multivariable linear regression model = 3.6%.

BMI, body mass index.

Discussion

To the best of our knowledge, this is the first study evaluating the proportion of persons with type 1 diabetes performing SMBG according to current guidelines of four times per day or more. A minority of patients (41%) fulfilled this criterion. Further, it shows that 30% of patients believed that fewer than 4 SMBG/day were recommended, and 11% believed that as few as ≤2 measurements/day were recommended. HbA1c was associated with frequency of SMBG measurements, but SMBG explained only a relatively small part of the HbA1c level. Older age and female sex were associated with more frequent SMBG than younger age and male sex.

Karter et al⁴ showed that 34% of persons with type 1 diabetes performed SMBG 3 times or more per day. Data were based on sales of test strips, an in-direct measure of SMBG. The study was performed at a single health maintenance organization (Kaiser Permanente). In a study by Miller et al,⁷ 93% of persons with type 1 diabetes self-reported performing SMBG three or more times per day, and 62% did so five or more times per day. This study included children, while a slightly lower testing frequency was seen in adults. Others^{12 13} have studied adherence to SMBG recommendations but did not report the actual frequency of SMBG measurements per day.

Several observational studies have shown an association between frequency of SMBG and HbA1c.^4–9 The extent to which the number of SMBG measurements explains HbA1c level in the present study is relatively low, although there was a statistically significant association (p<0.0001). Adjusted R-square for SMBG measurements during the last 30 days and HbA1c level at all clinics was 6.8%. This indicates that the number of SMBG measurements was estimated to explain around 7% of the HbA1c level, while other factors explain the remaining 93%. Therefore, other factors are likely crucial for obtaining good glycemic control. Hence, although a present focus is on the development of novel glucose monitoring systems such as CGM and Flash Glucose Monitoring, it is still important for clinicians to focus on other tools such as dietary advice, psychological interventions in certain patients, and insulin adjustments.^14–17

The correlation between HbA1c and SMBG may have been weakened by the fact that HbA1c was not measured using a standardized chronological distance to the questionnaire being fulfilled, but rather the mean of the two latest known values. However, this approach was chosen due to the apparent risk that patients more often measure blood glucose closer to clinic visits, thus leading to falsely higher results in the primary analysis of SMBG frequency. It is possible that lack of power may explain the lack of a significant association between HbA1c and SMBG measurements >7. A limitation to this study was that the devices used by patients were not calibrated nor of the same model. Differences in accuracy could theoretically affect HbA1c independently.^{18 19} However, public procurements in Sweden only allow blood glucose meters with a CV of <10%,²⁰ which ensures a relatively high level of precision.

Younger age was associated with performing fewer SMBG. Reporting not remembering SMBG was associated with fewer SMBG and younger age. Perhaps a different lifestyle with fewer routines in young adults explains some part of this finding. Men performed fewer SMBG. We found no sex differences in reported reasons for not performing more frequent SMBG. The finding that men perform fewer SMBG is consistent with previous studies.^{6 21} One explanation could be different attitudes towards exposing disease traits from a sociologic perspective.²²

In this study, we also attempted to estimate how patients with type 1 diabetes perceive they should measure blood glucose. Thirty percent of patients were not aware of recommended guidelines for SMBG measurements. A total of 70% of patients were aware of guidelines but only about 40% followed them. Pain from the measurement itself has previously been described as a primary reason for why patients do not perform SMBG.²³ In the present study, we found that only 14% of patients stated this as a main reason for not performing more frequent SMBG.

Instead, we found that about 50% of patients reported not remembering and lack of time as main reasons for not performing more frequent SMBG measurements. About 20% of patients reported self-consciousness as a main reason as well. Not remembering was associated with poorer glycemic control, higher insulin doses, and fewer SMBG. Our results indicate that psychological and lifestyle factors seem to play a substantial role in performing and not performing SMBG.

Data collection in this study was completed before FGM (ie, Freestyle Libre) was available, and hence availability of CGM or CGM-like equipment was lower than it is today. Hopefully, easier and less painful methods to measure glucose will increase the proportion of patients performing recommended numbers of measurements per day. However, studies on CGM have not yet shown drastic effects on HbA1c,²⁵ again emphasizing the importance of factors other than blood glucose monitoring. One problem with earlier studies on CGM and FGM is that they often focused on patients with rather good adherence to SMBG guidelines. Often, either inclusion criteria demanded adhering to SMBG ≥3–4 times per day^25–27 or the patient cohort had a mean SMBG measurement of >5 times per day.²⁴ In the present study, this would exclude >50% of the diabetes population in Sweden, despite the availability of free glucose meters and test strips.

Although our response rate was fairly high (≥70% at 3 sites), the frequency of SMBG measurements among non-participating patients may have been different, which to some extent may affect the resulting frequency in the population. Sites included in this study cover nearly 100% of patients with type 1 diabetes in their defined geographical areas and include different socioeconomic groups. Thus, our study population is believed to be a representative cross section of the population in Sweden. When comparing mean age, sex, diabetes duration, and HbA1c between nationwide data in Sweden and our cohort, the composition seems similar.²⁸ However, the fact that results may differ from those in other hospitals in Sweden due to different treatment patterns cannot be excluded, although this seems unlikely. In other countries where, for example, glucose strips are not available free of charge, adherence may be even lower.

In summary, this study shows that even though glucose meters and test strips are generally available at no cost in Sweden, <50% of patients measure capillary blood glucose levels four times per day or more. This indicates a need to further support performing SMBG by increased availability and continued development of IT tools and user-friendly glucose-monitoring devices. Previous studies have shown some promising effects on adherence to SMBG recommendations through education, problem solving, contingency management, goal setting, cognitive behavioral therapy, and motivational interviewing.²⁹ As a non-negligible proportion of patients with type 1 diabetes are not aware of SMBG guidelines, we also suggest that repeated and focused information may be essential to optimize glycemic control.

Acknowledgments

Footnotes

References