Hidradenitis suppurativa (HS) is characterized by a high inflammatory burden—often presenting with irritated nodules, abscesses, and fistulas in intertriginous areas. As such, lab markers such as c-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) can be useful indicators of degree of inflammation in HS.¹ Protein gap, another laboratory measure of inflammation, is defined as the difference between serum total protein and albumin levels.² Protein gap, like ESR and CRP, is often elevated in inflammatory conditions due to hypergammaglobulinemia.^3–5 However, little is known regarding the relationship between protein gap and the severity of hidradenitis suppurativa. Since late-stage HS is associated with plasma and B cell signatures and elevated immunoglobulin levels, we hypothesized that protein gap would positively correlate with HS severity and could be a useful marker of inflammatory burden.

In this study, we characterized the association between disease severity and protein gap levels for HS patients through retrospective chart review. Patients were included if diagnosed with HS (ICD code: ICD-10 code L73.2) and seen in the Duke Dermatology HS clinic with at least 1 follow-up appointment between July 1, 2018 and July 1, 2021. Patient demographics, disease characterization, and inflammatory markers were recorded. Severity of disease was measured by the International Hidradenitis Suppurativa Severity Score System (IHS4). Protein gap is reported from patients’ initial visit and was obtained through comprehensive metabolic panel.

The association between IHS4 and protein gap was assessed using univariable and multivariable linear regression models using log (IHS4) due to the violation of the normality assumption of raw IHS4 score. Additional covariates in the multivariable model included age, sex, smoking, body mass index (BMI), race, insulin resistance, hormone therapy, oral antibiotics, and immunomodulatory therapy. Model results are presented as the geometric mean ratio (GMR) with 95% confidence interval (CI). Pearson’s correlation coefficient (r) was also used to graphically evaluate the relationship between log (IHS4) and protein gap.

The final analysis consisted of 113 patients, with 82.3% self-reported female participants and 63.1% self-reporting as Black. Most of the patients included were never-smokers (54.1%) and did not have diabetes or prediabetes (56.4%). Full demographic characterization of the included patients is listed in Table 1. At their initial visit, included patients had a median (Q1-Q3) IHS4 score of 8 (2-28) and protein gap of 3.6 g/dL (3.2-4.5). We found that protein gap has a moderate to strong positive correlation with disease severity as measured by log (IHS4) (r=0.60, p<0.001) (Figure 1). Multivariable analysis further demonstrated that protein gap is associated with 2.24 times higher geometric mean IHS4 (95% CI: 1.69-2.96, p<0.001) per one unit increase in protein gap (Table 2).

298338 Table 1.

298339 Table 2.

Figure 1.

None