Effect of alkalinisation and increased fluid intake on bacterial phagocytosis and killing in urine.

The effect of alkalinisation and increased fluid intake on bacterial phagocytosis and killing in urine was studied. Phagocytosis of Escherichia coli and Staphylococcus saprophyticus by polymorphonuclear neutrophils (PMN) took place in only one of three first voided early morning urine samples from volunteers, and no bacterial killing occurred. This was attributed to the high osmolality (690 to 720 mOsm) and low pH of the early morning urine; two samples were pH 5.8 and the third, in which phagocytosis occurred, was pH 6.4. Afternoon urine samples from the same volunteers had lower osmolality and a higher pH, with a high rate of phagocytosis (> or = 88%) and 55-69% killing. PMN remained viable (mean 94%) after exposure for 1 h to both early morning and afternoon urine. Volunteers taking 4 g sodium citrate showed a mean rise of urinary pH of 1 unit. Water loading in patients with urinary tract infections produced a bacteria to neutrophil ratio conducive to bacterial killing, bacterial counts being reduced by a mean of 2.5 logs after 1-3 h without a corresponding reduction in neutrophils. Thus, raising the pH and reducing the osmolality of urine increases the ability of neutrophils to eliminate infecting organisms.