Objectives To relate blockage of the urinary catheter to urine chemist
ry. Patients and methods Of 44 patients (age range 19-72 years) with a
n indwelling urinary catheter, 21 were troubled by frequent blockage a
nd 23 experienced no blockage. Variation in urinary pH and calcium con
centration were determined during a 24 h period and related to the occ
urrence of blockage using discriminant analysis. Results The maximum p
H and calcium concentrations observed, or the maximum discriminant fac
tors calculated, correctly discriminated 91% of patients (95% CI, 78-9
7%). Conclusion Attention to volume and variability of fluid intake by
the patient should have a major impact on the incidence of blockage o
f the indwelling urinary catheter.