Twenty-four Hour and Spot Urine Metabolic Evaluations: Correlations Versus Agreements
Received 26 May 2009; accepted 26 August 2009. published online 16 November 2009.
Objectives
To investigate the correlations and agreements between the solute/creatinine ratios from the 24-hour and early morning spot urine samples for metabolic evaluation in stone-formers given the various pitfalls with the 24-hour urinary metabolic evaluation in stone-formers.
Methods
30 urinary stone-formers out of an initial 62 recruited provided a complete 24-hour urine and early morning spot urine samples for metabolic evaluation. Pearson correlation and Bland and Altman Test were used to assess the correlations and agreements.
Results
Significant correlations were established between the 24-hour urinary solute excretions and the corresponding early morning spot urine solute/creatinine ratios for calcium, magnesium, urate, potassium, oxalate, citrate, and the Differential Gibb's free energy value of calcium oxalate DG(CaOx) values. However, all these solute/creatinine measurements between the 24-hour and early morning spot urine samples were judged to be not within the acceptable limits based on the estimated “limit of agreement” by the Bland and Altman Test of Agreement. Diurnal circadian rhythm and postprandial excretion surge are thought to be responsible for the disagreements.
Conclusions
Thus, the early morning spot urine is not suitable to be used interchangeably to replace the 24-hour urine collection in the evaluation of urinary metabolic abnormalities in stone-formers. A good correlation does not translate to an agreement between the 2 measurements.
aDepartment of Physiology, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia
bDepartment of Surgery (Division of Urology), Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia
cDepartment of Pharmacology, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia
Reprint requests: Yet Hoi Hong, M.B.B.S., MMedSc, Department of Physiology, Faculty of Medicine, University of Malaya, 50603, Kuala Lumpur, Malaysia
This project was funded under the University of Malaya Research Grant (Vote-F: FS 154/2007C), Kuala Lumpur, Malaysia.
ABSTRACT