Background: Developing a simple quantitative tool for mastitis diagnosis is essential. The Ion-Selective Electrode for sodium has been reported to reliably measure sodium concentrations in human milk. Research Aim: To determine whether an Ion-Selective Electrode measurement of sodium:potassium ratios could serve as a diagnostic tool for mastitis and, if so, to determine the diagnostic cut-off value. Methods: A total of 107 milk samples, including 55 from milk bank donors and 52 from participants with mastitis, were studied. The sodium:potassium ratios were determined in 33 samples (without mastitis n = 15; with mastitis n = 18) by the Ion-Selective Electrode and ion chromatography. The remaining 74 samples (donor milk n = 40; participants with mastitis n = 34) were analyzed by Ion-Selective Electrode only. Values were averaged over three measurements for each method. Results: The median postpartum months of donors and participants with mastitis were 2 and 3 months, respectively. The mean ( SD) sodium:potassium ratios without and with mastitis were 0.5 (0.1) and 1.7 (1.2), respectively. A positive correlation existed between sodium:potassium ratios obtained from the two methods ( r = 0.98). Area under the curve values were 0.951 (95% CI [0.904, 0.986]) for the Ion-Selective Electrode ( N = 107) and 0.978 (95% CI [0.926, 1.000]) for the ion chromatography ( n = 33) methods. The optimal cut-off value for the Ion-Selective Electrode method was 0.60, with 86.5% sensitivity and 92.7% specificity. Conclusions: The Ion-Selective Electrode was sufficiently accurate for the diagnosis of mastitis. Cohort studies are needed to explore the relationship between sodium:potassium ratios and clinical outcomes.

Background: Microwave heating can be effective in preventing cytomegalovirus infection transmitted via human milk. Temperature changes during microwaving using different containers, in different areas inside a container, or using milk from different mothers are not well studied. Research Aim: To determine temperature changes of human milk during microwaving using different containers, in different container areas, using different human milk, and in a 30-ml soft polypropylene bag (sachet) immersed in water. Methods: In this experimental in vitro study, human milk (100 ml) was poured into six different bottles. The temperature was monitored simultaneously at each bottle’s bottom and surface (microwaving at 600 W) and at nine places inside the container (microwaving at 500 W). Human milk (20 ml) from six participants was inserted into a sachet, then immersed in 80 ml of human milk or water in a bottle, and the temperatures inside and outside the sachet during microwaving (at 500 W) were monitored. Results: The temperature changes at the surface were significantly larger than those at the bottom. Temperatures at the bottoms of different bottles, of human milk from different participants, or inside and outside the sachet, did not differ significantly. No temperature outliers inside the bottle were observed. Conclusion: Microwaving at 500 W and 600 W for 60 s was not significantly different in temperature changes among different areas inside bottles or among milk from different participants. A small volume of human milk (up to 100 mL) can be heated using a sachet.

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We aimed to evaluate if human milk-based fortifier (HMBF) affects human milk fat globule (MFG) size less than cow milk-based fortifier (CMBF), which may impact overall infant feeding tolerance. Measurements of donated human milk were performed before fortification as well as at 1 hour, 24 hours, and 48 hours after fortification with CMBF or HMBF. MFG size in each sample of fortified milk was measured by laser light scattering. MFG size in the fortified milks increased gradually over time. At 24 and 48 hours after fortification, MFG size in the milk with CMBF was larger than that in the milk with HMBF (4.8 ± 0.5 vs 4.3 ± 0.3 μm, p<0.01, 5.1 ± 0.7 vs 4.5 ± 0.4 μm, p = 0.03, respectively). HMBF is associated with less alteration of MFG size than CMBF. This may have an impact on feeding tolerance of very preterm infants.