Wounds were assessed for STONEES criteria, including the probe-to-bone test (Os) and then added to determine a total number of criteria present; three or more indicated deep or surrounding wound infection. For a positive Os (exposed bone) criterion, an anterior-posterior and oblique view X-ray was requested to determine the presence of underlying osteomyelitis or untreated Charcot foot complications to expedite orthopedic intervention and antibiotic treatment as depicted in Figure 1 (see also Figures 2 and 3).
Quantifiable wound status data using three-dimensional photography (Silhouette camera; ARANZ Medical, Christchurch, New Zealand) were used to calculate surface area/percentage of healing achieved and presented in a linear progress graph. Because all existing patients had this photographic data prospectively collected (it is a standard assessment modality used during visits to the authors’ unit), it was a valid assessment set to analyze. All new patients were assessed in the same manner and followed up for the duration of the study.
All data were entered into a spreadsheet by the investigators after verifying every finding with laboratory results, X-rays, and daily wound documentation sheets. The statistician who was involved in the analysis transferred that spreadsheet into SPSS 13.0 (IBM Corp, Armonk, New York) to perform one-way analysis of variance, Spearman correlation analysis, and χ2 tests.
In an attempt to model the relationship between the independent variable (variation of wound status) and some of the dependent variables (either in isolation or together) in this study, general linear models were created (with wound size as the dependent variable). One of the outcomes is known as the R2 value, depicting a statistical measure of how closely the data are connected to the established regression line. As additional measurement, an adjusted R2 could be employed to support the initial R2 after adjustment for the number of predictors present in the linear model. The adjusted R2 increases only if statistical adjustment improves the model more than would be expected by chance and is more reliable than R2 alone.
Of the total sample (N = 80), 48% were older than 60 years (mean, 50 years), and 71.3% were male (Table 1). Diabetes mellitus was present in 90% of participants (n = 72), and an HbA1c greater than 6.8% was found in 62.5% (n = 45). An HbA1c in excess of 10% (indicating severe poor glycemic control; mean HbA1c, 8.15 was present in 13 patients with diabetes. Of the total sample, 76.3% (n = 61) had both diabetes mellitus and a 25(OH)D deficiency.
Because of wound complexity, prolonged wound duration (ie, wounds slow to heal, stalled, or deteriorated; mean, 138 days; range, 0–490 days) was found in 78.8% (n = 63) of the sample (Table 1). Wound parameter such as an increased surface temperature 3° F or more (mean, 4.3° F) was present in 82.5% of the sample (n = 66). Three or more STONEES criteria (with or without exposed bone) were found in 57.5%, (n = 46) with an overall mean of 2.5 STONEES criteria per person (Table 2).
The mean achieved 25(OH)D level was 12.4 (SD, 7.8) ng/mL (range, 4.2–49.02 ng/mL), indicative of severe 25(OH)D deficiency. Cross-tabulated findings revealed that 25(OH)D deficiency (<#20 ng/mL) was present in 91.3% of females and 82.4% of males (Table 3). When compared with the subgroup of participants with diabetes with an elevated HbA1c (>#6.8%; n = 50), 88% (n = 44) demonstrated a 25(OH)D deficiency of less than 20 ng/mL (Table 3).
Mean wound healing achieved per week was 1.48%, or 5.9% per 30 days, much lower than the 30% per 4 weeks’ progress expected of healable wounds.21 A slow healing rate was present in 38.8% (n = 31) of the total sample (Table 1), but of the subgroup of patients with diabetes (n = 72), 41.6% (n = 30) showed slow healing, and 25% had deteriorating wounds (n = 18).
An increased surface temperature of more than 3° F was recorded over a contralateral mirror-image comparator in 82.5% (n = 66) of the patients (Tables 1 and 3). An exposed bone in the wound bed (positive Os criterion, as seen in Figures 2 and 3) was present in 33 persons with 25(OH)D deficiency (41.3%; Table 3) and 35 persons with diabetes (48.6%; Table 4).
Statistically Significant Findings
Poor wound healing was statistically associated with both older age and higher HbA1c levels (P < .0001) on the one-way analysis of variance test. A further link was present between poor wound healing where three or more STONEES criteria, an exposed bone in the wound bed, or a 3° F temperature difference was present in the surrounding skin (P < .006).
The Spearman two-tailed test using a 1% level of significance correlated poor wound healing outcomes with older age as well as lower 25(OH)D levels. Correlations at this same level of significance were also present between older age and
- a 3° F or greater local versus contralateral mirror-image temperature increase,
- patients with three or more STONEES criteria (including the aforementioned temperature increase); and
- a wound with exposed bone (Os criterion).
Further correlations between length of wound duration and male sex and wound deterioration over time with either STONEES’ Os or Temperature criteria were also present (P = .05).
General Linear Modeling
Using adjusted R2 values (Table 5), the combination of 25(OH)D and the presence of three or more STONEES criteria could only explain 8.9% of the variation in achieved wound healing status. When considering 25(OH)D and glycemic control, this value dropped to 3.2%. However, with the addition of a third factor (three or more positive STONEES criteria), 31.3% of the achieved wound healing status could be explained. When two metabolic markers (25[OH]D and HbA1c) were compared with a separate wound-related criterion from the STONEES set, it clearly revealed that an exposed bone in the wound bed (positive Os criterion) could explain 49.4% of the variation in achieved wound healing status.
General Linear Modeling of Patients with Diabetes
The data of all persons with diabetes (n = 72) were analyzed separately to eliminate any confounding effects that the patients without diabetes may have had on the first round of general linear modeling (Table 6). 25(OH)D and the presence of three or more STONEES criteria increased the adjusted R2 score from 8.9% in the total sample to 17.1% in the diabetes-only group. The adjusted R2 value for 25(OH)D, glycemic control, and the presence of three or more STONEES criteria increased from 31.3% to 42.1%. These three factors therefore played a larger role in the achieved wound healing status of a patient with diabetes as compared with participants overall. Exposed bone remained an important criterion together with low 25(OH)D levels and poor glycemic control, explaining 47.9% of the wound outcomes.
In a study of 500 healthy Bahraini blood donors3 without diabetes, 49.4% had 25(OH)D concentrations of less than 20 ng/mL; clearly, the Bahraini population is at general risk of 25(OH)D deficiency. This is further supported by research such as the mother and newborn study4 and in the fathers of those newborns.5
In this study, 72 patients with diabetes and wound-related complications were documented as part of the sample. 25(OH)D deficiency (<#20 ng/mL) was present in 61 of those patients (84.7%). This finding supports previous research in that patients who are diabetic with poor glycemic control are prone to 25(OH)D deficiency.7–10 This study also identified that this finding is more likely with a diabetes-related open wound present on the foot. Further, these findings support the correlation between older age coupled with both 25(OH)D deficiency and poor glycemic control.22,23
It is accepted in literature that males are more likely to have diabetes-related complications,24–26 which may also include foot-related wounds. The results found in the males of this sample confirm this observation. However, the high presence of 25(OH)D deficiency found in the male population (82.4%) compared with 91.3% of the female population was an unexpected finding. In this study, the male sex was not protective against 25(OH)D deficiency when diabetes and a wound-related complication were comorbidities.
The overall severity of 25(OH)D deficiency found in this study (85%) is suggestive that the presence of a diabetes-related wound may be a positive indicator of a potential low 25(OH)D level. When 25(OH)D deficiency was compared with wound infection markers, half of the sample had either a positive Temperature criterion, Os criterion, or STONEES set of three or more criteria present. When those markers were compared with the maintenance of glycemic control, half of the sample again had an exposed bone, along with two or more other STONEES clinical signs present.
Of note, more than two-thirds of patients with a 25(OH)D deficiency presented with a positive increase in surface temperature over a mirror-image site, indicating a high likelihood of the presence of deep or surrounding wound infection.17–19 A 3° F temperature increase on a foot of an individual with diabetes, even without additional STONEES criteria, should not be ignored. It may be indicative of sustained tissue trauma that could lead to ulcer formation. High-quality self-monitoring studies of patients with diabetes27–29 have confirmed that a 3° to 4° F temperature increase on any area of the foot should be followed by plantar pressure redistribution and rest until the temperature subsides to prevent subsequent skin breakdown.
In this study, the inability of a wound to heal could not conclusively be attributed to a 25(OH)D deficiency, poor glycemic control, or even the presence of local infection markers individually, although it does support the studied 25(OH)D deficiency trend already identified in the Bahraini population4–6 and also supports that 25(OH)D deficiency is associated with diabetes mellitus.8–10,22–26 However, the simultaneous identification of local wound bed status indicators was important. Surface temperature differentials and a positive STONEES set of three or more clinical signs positively correlated to poor wound outcomes in the presence of either 25(OH)D deficiency or poor glycemic control.
The study facility is located in a tertiary care hospital with hyperbaric oxygen therapy chambers. Most patients referred here are those with DFU (Wagner grade 3 or higher) complications and live within a confined island population. The study was designed to incorporate a small consecutive sample (N = 80) over a short study period to remain within reasonable clinical expenditure. These results should therefore be contextualized by the fact that this is a cross-sectional pilot study designed to support the premise that 25(OH)D deficiency should be considered when wound healing difficulty in persons with diabetes-related wound complications is encountered.
By designing an RCT as a follow-up to this cross-sectional study, the causal link supported by these results could be scientifically validated, defining 25(OH)D levels as an important cofactor that delays or prevents DFU healing. Prospective scientific studies (ideally RCTs) are required to demonstrate that patients with diabetes receiving 25(OH)D supplementation can obtain sufficient serum levels to support wound healing. These sufficient levels need to be linked to improved HbA1c levels and accelerated ulcer healing along with the management of the signs of infection.
In this study, a correlation was found between poor wound healing outcomes and the presence of poorly controlled diabetes mellitus and 25(OH)D deficiency. These factors were detrimental to the ability of wounds to avoid deep and surrounding wound infection (especially with increased surface temperature or an exposed bone present in the base of the wound bed). It also added to a delay in achieving the expected 12-week wound healing trajectory.
Vitamin D status may be an overlooked factor in the pathophysiology of DFU development and subsequent delay in wound healing outcomes. The strongest statistical associations (adjusted R2 = 49.4%) linked delayed DFU healing in participants with diabetes to 25(OH)D deficiency, poor glycemic control, and exposed bone in the wound bed.
As a result of this study, the initial wound assessment protocol at the study facility has changed; providers now obtain 25(OH)D and HbA1c levels simultaneously with the standard wound assessment procedures. This approach aids providers in considering multifactorial aggravating factors in this subgroup of patients as part of a holistic care plan.21
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Keywords:Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.
25-hydroxyvitamin D; Bahrain; diabetes; diabetic foot ulcer; exposed bone; glycemic index; HbA1c; vitamin D; vitamin deficiency; 25(OH)D; wound healing; wound infection