['Mother-to-child transmission (MTCT) of HIV-1 has been associated with symptomatic and asymptomatic mastitis and with the quantity of HIV-1 RNA and DNA in maternal milk. An improved understanding of the relationship between indicators of inflammation and HIV-1 loads in breast milk could improve MTCT prevention strategies.', 'In a cross-sectional study, laboratory indicators of mastitis (breast milk sodium [Na(+)] concentration, sodium : potassium ratio [Na(+) : K(+)], and leukocyte count) were related to breast milk HIV-1 RNA and DNA loads and were evaluated for predicting viral loads in milk.', 'Mastitis was present in 63 (15%) of 407, 60 (15%) of 407, and 76 (18%) of 412 milk specimens, as defined by Na(+) concentration >12 mmol/L, Na(+) : K(+) >1, and total leukocyte counts > or =10(6) cells/mL, respectively. Each indicator was associated with an increased milk HIV-1 RNA load (P<.05) but not with HIV-1 DNA load. Neutrophils correlated better with milk HIV-1 RNA load than total leukocytes. However, neither neutrophil count, Na(+) concentration, nor Na(+) : K(+) displayed a threshold that was both sensitive and specific for the detection of HIV-1 RNA in milk at thresholds of > or =50 or > or =10(4) copies/mL.'] Are laboratory indicators of mastitis associated with elevated HIV-1 DNA loads or predictive of HIV-1 RNA loads in breast milk?