Effects of sex-by-age category (16–45 years <i>vs</i>. 56–80 years) interaction on ranked coefficients of variation (<i>CV</i> = <i>σ/μ</i>) calculated from original paired 24-h urinary solutes (urinary ammonium (NH₃), calcium (Ca), chloride (Cl), citrate (Cit), potassium (K), magnesium (Mg), sodium (Na), oxalate (Ox), phosphorus (P), sulfate (SO₄), uric acid (UA), urine urea nitrogen (UN)) collected from 6,758 female and 9,024 male stone-formers aged 16–80 at the False Discovery Rate [Verhoeven, 2005 #22836].

<p>Effects of sex-by-age category (16–45 years <i>vs</i>. 56–80 years) interaction on ranked coefficients of variation (<i>CV</i> = <i>σ/μ</i>) calculated from original paired 24-h urinary solutes (urinary ammonium (NH₃), calcium (Ca), chloride (Cl), citrate (Cit), potassium (K), magnesium (Mg), sodium (Na), oxalate (Ox), phosphorus (P), sulfate (SO₄), uric acid (UA), urine urea nitrogen (UN)) collected from 6,758 female and 9,024 male stone-formers aged 16–80 at the False Discovery Rate [Verhoeven, 2005 #22836].</p

Effects of Sex on Intra-Individual Variance in Urinary Solutes in Stone-Formers Collected from a Single Clinical Laboratory

<div><p>Background/Aims</p><p>Our work in a rodent model of urinary calcium suggests genetic and gender effects on increased residual variability in urine chemistries. Based on these findings, we hypothesized that sex would similarly be associated with residual variation in human urine solutes. Sex-related effects on residuals might affect the establishment of physiological baselines and error in medical assays.</p><p>Methods</p><p>We tested the effects of sex on residual variation in urine chemistry by estimating coefficients of variation (<i>CV</i>) for urinary solutes in paired sequential 24-h urines (≤72 hour interval) in 6,758 females and 9,024 males aged 16–80 submitted to a clinical laboratory.</p><p>Results</p><p>Females had higher <i>CV</i>s than males for urinary phosphorus overall at the False Discovery Rate (<i>P</i><0.01). There was no effect of sex on <i>CV</i> for calcium (<i>P</i>>0.3). Males had higher <i>CV</i>s for citrate (<i>P</i><0.01) from ages 16–45 and females higher <i>CV</i>s for citrate (<i>P</i><0.01) from ages 56–80, suggesting effects of an extant oestral cycle on residual variance.</p><p>Conclusions</p><p>Our findings indicate the effects of sex on residual variance of the excretion of urinary solutes including phosphorus and citrate; differences in <i>CV</i> by sex might reflect dietary lability, differences in the fidelity of reporting or genetic differentiation in renal solute consistency. Such an effect could complicate medical analysis by the addition of random error to phenotypic assays. Renal analysis might require explicit incorporation of heterogeneity among factorial effects, and for sex in particular.</p></div

Effects of gender on ranked coefficients of variation (<i>CV</i>) from paired 24-h urinary measurements of urinary ammonium (NH₃), calcium (Ca), chloride (Cl), citrate (Cit), potassium (K), magnesium (Mg), sodium (Na), oxalate (Ox), phosphorus (P), sulfate (SO₄), uric acid (UA) and urine urea nitrogen (UN) adjusted for creatinine, urinary volume, age and weight in the complete population of 6,758 females and 9,024 males aged 16–80, and in individuals aged 16–45 and 56–80 in a stepwise backward regression (<i>P</i>_acceptance≤0.1).

<p>Significance (below) is corrected for multiple observations via False Discovery Rate [Verhoeven, 2005 #22836]. Nominal <i>P</i>-value (<i>P</i>_nom) is reported at acceptance or removal from the model during the stepwise procedure. Units indicates original values used in <i>CV</i> calculation.</p><p><i>P</i>_nom = nominal <i>P</i>-value.</p>*<p><i>P</i>_FDR<0.05,</p>**<p><i>P</i>_FDR<0.01.</p><p>Correlation coefficients (<i>r</i>²) refer to the complete model correlation, or model fit at rejection of nonsignificant terms via backwards regression (removal at <i>P</i>>0.1).</p><p>Negative <i>β</i> indicates lower female <i>CV</i>; positive <i>β</i> higher male CV.</p

Mean ranked coefficients of variation (<i>CV</i>) for chloride (Cl), magnesium (Mg), sodium (Na), oxalate (Ox) and phosphorus (P) in a complete population of 6,758 females and 9,024 males submitted to Litholink, Inc.

<p><b>significant at nominal (Cl, Mg, Na and Ox) and </b><b><i>α</i></b><b>_0.05 False Discovery Rate thresholds selected using backwards stepwise regression (</b><b><i>P</i></b><b>_acceptance = 0.1).</b><b> </b></p

Mean ranked coefficients of variation (<i>CV</i>) for citrate (Cit), chloride (Cl), potassium (K), magnesium (Mg) and phosphorus (P) in 4097 females (F) and 4014 males (M) in an approximate ‘menarche-menstrual’ (MM) period (ages 16–45) and in 1715 females and 3479 males in an approximate ‘postmenopausal’ group (PM) (ages 56–80).

<p>Significance of differences in <i>CV</i> by trait and age group (MM <i>vs</i>. PM) indicated as <i>P</i><0.05*, <i>P</i><0.01**.</p

Mean coefficients of variation () and minimum and maximum <i>CV</i>s for urinary (Ca; mg), citrate (Cit; mg), chloride (Cl; mmoles), creatinine (Cr; mg), potassium (K; mmoles), sodium (Na; mmoles), magnesium (Mg; mg), oxalate (Ox; mg), phosphorus (P; g), ammonium (NH₄; mmoles), sulfate (SO₄; meq), uric acid (UA; g) and urea nitrogen (UN; mg) within a complete population of 9,024 male and 6,758 female kidney stone patients aged 16–80, and in individuals aged 16–45 and 56–80.

<p>CV values approaching zero reflect exact measurements on both sampling days for small numbers of observations.</p