A statistical comparison of pad numbers versus pad weights in the quantification of urinary incontinence

Pad per day (PPD) usage is a frequently utilized measure of urinary incontinence. The 24-hour pad weight test (24PWT) is a reproducible test for quantifying incontinence volumes. We investigated whether PPD validly reports the magnitude of urinary incontinence. Methods: This was a retrospective review of patients undergoing stress incontinence surgery front July 2002 to 2005. Inclusion criteria were a documented 24PWT and patient-reported PPD usage. Grains of urine loss per pad (GPP) provided a third measure of incontinence. Descriptive statistics and correlations between all variables and significance were noted. Factor analysis was performed on the three measures of leakage and age for all patients over age 50. Results: One hundred forty-five male and 116 female patients met inclusion criteria. Correlated against 24PWT, GPP has the strongest association with a correlation of 0.80 for males and 0.88 for females. PPD has a weaker correlation of 0.64 for males and 0.61 for females (R-2 = 0.38 overall). Factor analysis identified two components associated with incontinence. A "leakage" component correlated belt with 24PWT and GPP. Additionally, an "age" component implies that despite stable 24PWT values, older patients increase GPP while PPD decreases. Conclusions: Self-reported PPD is an unreliable measure of incontinence as this variable only measures 38% of the variation of urinary incontinence volume. Patients at a given PPD level present with a wide range of 24PWT values. Older patients have higher per-pad leakage. Future incontinence studies should report 24PWT to ensure the most reliable and uniform data.