Comparing 24 h Urine and Spot Urine Calcium Measurements in Clinical Routine: Accuracy and Limitations.

Assessing urinary calcium levels is essential for diagnosing conditions like nephrolithiasis and hyperparathyroidism. The gold standard remains 24-hour urine collection, which is widely accepted but often difficult to implement in clinical settings due to compliance and logistical issues. Researchers have proposed using spot urine samples with calcium-to-creatinine ratios (CCR) as a more convenient alternative. However, the reliability of spot urine CCR for diagnosing hypercalciuria remains uncertain. Prior studies have shown mixed results, with some suggesting moderate diagnostic accuracy and others indicating significant variability. This uncertainty has motivated investigations into whether spot urine can reliably substitute 24-hour urine in clinical practice. No prior work has resolved the extent to which spot urine CCR can be used as a diagnostic tool. The gap in understanding the agreement and limitations of spot urine measurements has driven recent research efforts. Existing evidence suggests a need for systematic comparison between the two methods. This paper contributes by analyzing the diagnostic accuracy and agreement of spot urine CCR against 24-hour urine measurements.

The aim of this study is to evaluate the diagnostic accuracy and agreement between spot urine calcium-to-creatinine ratios and 24-hour urine calcium excretion. The specific problem addressed is whether spot urine CCR can serve as a reliable alternative to 24-hour urine collection in clinical settings. Researchers sought to determine how well spot urine CCR correlates with 24-hour urine calcium levels. The motivation stems from the practical limitations of 24-hour urine collection, which often leads to patient non-compliance and incomplete samples. By analyzing a multi-center dataset, the study aims to provide evidence on the clinical utility of spot urine CCR. The study also examines the sensitivity and specificity of spot urine CCR for detecting hypercalciuria. The researchers focused on defining optimal cut-off values for diagnosing hypercalciuria using spot urine measurements. This work is intended to guide clinicians in deciding when and how to use spot urine CCR in routine diagnostics.

The study employed a retrospective, multi-center design using data from 201 patients who provided both 24-hour and spot urine samples. Researchers normalized calcium excretion using the calcium-to-creatinine ratio (CCR) in both sample types. They assessed agreement between the two methods using Bland-Altman analysis to calculate mean differences and limits of agreement. Pearson and Spearman correlation coefficients were used to evaluate the strength of the relationship between spot and 24-hour urine CCR. Receiver operating characteristic (ROC) curve analysis was performed to determine diagnostic accuracy and identify optimal cut-off values. Hypercalciuria was defined as ≥6.25 mmol/24 h in women and ≥7.5 mmol/24 h in men. The study focused on calculating sensitivity, specificity, and predictive values for spot urine CCR. Data were collected from routine diagnostic work-ups between January 2019 and December 2024.

Hypercalciuria was detected in 52.7% of cases based on 24-hour urine measurements. ROC analysis revealed a moderate diagnostic accuracy for spot urine CCR, with an area under the curve (AUC) of 0.76. The optimal cut-off for predicting hypercalciuria was 4.4 mmol/g, achieving 70.8% sensitivity and 72.4% specificity. Bland-Altman analysis showed a geometric mean ratio of 1.06 between spot and 24-hour urine CCR. The multiplicative limits of agreement ranged from 0.59 to 1.91, indicating moderate agreement. A spot urine CCR below 2 mmol/g had high sensitivity (82%) but low specificity for ruling out hypercalciuria. The negative predictive value of low spot urine CCR was 82%, suggesting limited utility in certain cases. These findings suggest that spot urine CCR cannot fully replace 24-hour urine collection for diagnosing hypercalciuria.

The authors concluded that spot urine CCR cannot replace 24-hour urine collection for accurately assessing urinary calcium excretion. However, very low spot urine CCR values may have limited utility as an initial rule-out tool in selected patients. The study found that spot urine CCR had moderate diagnostic accuracy and agreement with 24-hour urine measurements. The proposed cut-off of 4.4 mmol/g achieved acceptable sensitivity and specificity for predicting hypercalciuria. Researchers observed that low CCR values below 2 mmol/g had high sensitivity but low specificity for ruling out hypercalciuria. These findings suggest that spot urine CCR may support triage decisions in specific clinical situations. The authors propose that further prospective studies are needed to validate these findings. They emphasize the importance of using 24-hour urine collection as the gold standard in clinical practice.