Electrolyte concentration and electrical conductivity of milk: ability to predict lactational mastitis status—A prospective cohort study

Background Lactational mastitis (LM) is a common and painful postpartum condition. While studies in dairy animals have shown that milk electrolytes and electrical conductivity (EC) can indicate inflammation, human research is scarce. This study compares breast milk electrolyte levels and EC between healthy lactating women and those with LM to improve diagnostic accuracy for this condition. Methods We collected bilateral breast milk from 119 lactating healthy women and 121 women with LM, recorded their clinical characteristics and explored the differences in milk electrolyte concentrations and EC. And then, the self-comparison of conductivity and EC in the inflammation group were recorded, the comparison of mean values in the infected group and the healthy group were conducted. Results indicated differences in electrolyte concentrations and EC between mastitis patients and healthy women. A preliminary optimal cut-off value was established and evaluated for its diagnostic utility in initial LM detection. Results This study included 119 healthy postpartum women and 121 patients with LM. No significant differences in Na⁺, K⁺, Cl⁻, Ca²⁺, or EC were found between left and right breasts in the healthy group. In the LM group, all parameters were significantly higher in affected versus unaffected breasts. All measures were also significantly elevated in the mastitis group compared to the healthy group. Based on these findings, preliminary diagnostic cutoff values were established: Na⁺ (14.300 mmol/L), K⁺ (16.985 mmol/L), Cl⁻ (14.688 mmol/L), Ca²⁺ (6.055 mmol/L), and EC (1.475 mS/cm), offering objective criteria for clinical detection of LM. Conclusions LM incidence is rising and remains a major reason for breastfeeding cessation. Current diagnosis relies on empirical assessment due to the absence of specific diagnostic criteria. Previous animal studies have linked mammary inflammation to alterations in breast milk Na⁺, K⁺, Cl⁻, and Ca²⁺ levels and EC. Our study proposes preliminary cutoff values for these parameters to aid in accurate detection of mammary inflammation, potentially helping to improve breastfeeding continuation rates.