HbA1c and wound infection
A chronic state of impaired glucose metabolism has long been
demonstrated to affect components of the immune system, thereby meaning
HbA1c may impact the rate of post-operative infections. Post-operative
wound infection affects patient morbidity and length of stay in hospital
following cardiac surgery and hence it is important to analyse the
relationship between HbA1c levels and infection rate. Some studies that
have been carried out have shown that HbA1c level has no effect on the
rate of wound infection 28,30,32,39,41. By contrast,
far more studies have demonstrated that elevated HbA1c levels are
associated with increased rate of wound infection20,21,23,26,29,34–37,40,42. The main outcomes from
these studies are summarised in Table 3 and Table 4.
Biskupski et al 39 analysed outcomes in 350
patients who were stratified into three groups according to HbA1c
levels: <7.0%, 7.0-8.0%, and >8.0%. The study
found that there was no significant difference in the incidence of wound
infection for the group with HbA1c <7.0% when compared to
those with HbA1c 7.0-8.0% and to those with HbA1c >8.0%
(1.53% vs 3.40%, P= 0.57 and 1.53% vs 5.97%, P= 0.13
respectively). These findings were replicated in two further studies
which showed that HbA1c level had no effect on the incidence of wound
infection. In a study where the primary outcome analysed was the
incidence of wound infections, it was found that there was no
statistically significant difference in the rate of all subset of wound
infection in patients with HbA1c <7.0% and in those with
HbA1c >7.0% (P=0.431 and P=0.744 for sternal and
non-sternal infections respectively) 42.
By contrast, Gatti et al 41 specifically looked
at whether HbA1c was a risk factor for sternal wound infection following
CABG surgery in 2,130 patients and found that the mean baseline HbA1c
level was significantly higher in patients who had sternal wound
infection (54±17mmol/mol vs 45±13mmol/mol; P< 0.0001).
Logistic regression showed that HbA1c level was an independent risk
factor for sternal wound infection (OR 1.04; 95% CI 1.02-1.05;P< 0.0001) with an HbA1c level greater than 8.6% being
associated with the highest risk of sternal wound infection (OR 5.01;
95% CI 2.47-10.15). Similar results were shown in a range of other
studies which all showed that pre-operative elevated HbA1c was
associated with increased incidence of both sternal and non-sternal
wound infection.
Overall the evidence suggests that elevated HbA1c level is associated
with an increased incidence of wound infection in cardiac surgery
patients but it is unclear if there is a specific level of HbA1c
associated with this increased incidence which could serve as a target
for pre-operative glycaemic control as studies used a range of HbA1c
cut-offs in their analyses. Yet, further work is required to determine
the exact cut-off level and association of HbA1C level and non-sternal
wound infections.