Urinary protein/creatinine ratio weighted by estimated urinary creatinine improves the accuracy of predicting daily proteinuria

The correlation of spot urinary protein-to-creatinine ratio with 24-h urinary protein excretion in various glomerulopathies

BACKGROUND

Proteinuria is an important and well-known biomarker of many forms of kidney injury. Its quantitation is of particular importance in the diagnosis and management of glomerular diseases. Its quantification can be done by several methods. Among these, the measurement of 24-h urinary protein excretion is the gold standard method. However, it is cumbersome, time-consuming, and inconvenient for patients and is not completely foolproof. Many alternative methods have been tested over time albeit with conflicting results. Among the latter, the measurement of urine protein-to-creatinine ratio (uPCR) in single-voided urinary samples is widely used. The majority of studies found a good correlation between uPCR in single urine samples with 24-h urinary protein estimation, whereas others did not.

AIM

To investigate the correlation of spot uPCR with 24-h urinary protein estimation in patients suffering from different forms of glomerulopathies at a single large-volume nephrological center in Pakistan.

METHODS

This cross-sectional, observational study was conducted at the Department of Nephrology, Sindh Institute of Urology and Transplantation, Karachi, Pakistan from September 2017 to March 2018. All newly presenting adult patients with proteinuria who were being investigated for suspected glomerulonephritis and persistent proteinuria with ages between 18 to 60 years were enrolled. All patients were given detailed advice regarding 24-h urine collection starting at 7:00 AM for total protein and creatinine excretion estimations. A spot urine sample was collected the next day at the time of submission of a 24-h urine sample for measuring uPCR along with a blood sample. The data of patients were collected in a proforma. SPSS version 20.0 was used for statistical analysis.

RESULTS

A total of 157 patients were included. Their mean age was 30.45 ± 12.11 years. There were 94 (59.8%) males and 63 (40.2%) females. The mean 24-h urinary protein excretion was 3192.78 ± 1959.79 mg and the mean spot uPCR was 3.16 ± 1.52 in all patients. A weak but significant correlation was observed between spot uPCR and 24-h urinary protein excretion (r = 0.342, P = 0.01) among all patients. On subgroup analysis, a slightly better correlation was found in patients older than 47 years (r = 0.78), and those with body mass index > 25 kg/m2 (r = 0.45). The Bland and Altman's plot analysis comparing the differences between spot uPCR and 24-h protein measurement also showed a wide range of the limits of agreement between the two methods.

CONCLUSION

Overall, the results from this study showed a significant and weakly positive correlation between spot uPCR and 24-h urinary protein estimation in different forms of glomerulopathies. The agreement between the two methods was also poor. Hence, there is a need for careful interpretation of the ratio in an unselected group of patients with kidney disease.

Withstanding the test of time: Morning versus afternoon/evening urine protein-to-creatinine ratios in preeclampsia

OBJECTIVE

There are mixed findings regarding time preference for measuring spot urine protein to creatinine ratios (UPCR) in renal patients but no such literature among pregnant patients. We compare AM versus PM measurements for UPCR among pregnant patients with preeclampsia.

STUDY DESIGN

This retrospective study included 163 patients diagnosed with preeclampsia. Laboratory tests of UPCR, urine specificity gravity, and uric acid were collected for these patients during the morning (AM) 12:00 AM (00:00) through 11:59 AM (11:59) and afternoon/evening (PM) 12:00 PM (12:00) through 11:59 PM (23:59).

MAIN OUTCOME MEASURES

Outcomes were UPCR percentages indicative of preeclampsia, UPCR median values, abnormal uric acid, and normal urine specific gravity indicative of a quality sample for measuring UPCR.

RESULTS

UPCR ≥ 0.3 indicative of preeclampsia significantly differed (p < 0.001) where the AM group (76.7 %) had a greater percentage than the PM group (52.8 %). Median UPCR significantly differed (p < 0.001) where the AM group had a greater median (0.44) than the PM group (0.32). None of the uric acid or urine specific gravity comparisons significantly differed between the AM and PM groups. Similar patterns occurred for subgroups of those with hypertension, nulliparous, and preeclampsia with severe features.

CONCLUSION

We found that UPCR had greater median values and more values indicative of preeclampsia for AM measurements than PM measurements. Clinicians who use spot urine measurements and not 24-hour urine measurements should preferably measure UPCR in the AM rather than the PM.

Diagnostic efficacy and influence factors of urinary protein/creatinine ratio replacing 24-h urine protein as an evaluator of proteinuria in children

PURPOSE

The aim was to investigate the diagnostic efficacy of urinary protein/creatinine ratio (UPCR) and factors influencing its substitutability of 24-h urine protein (24hUP) in children with proteinuria.

METHODS

A total of 356 children were recruited, including 149 with non-nephrotic-range proteinuria and 207 with nephrotic-range proteinuria which were further divided into Henoch-Schönlein purpura nephritis (HSPN), lupus nephritis (LN), and primary nephrotic syndrome (PNS). The urine protein and creatinine were measured by routine methods. Bland-Altman analysis was used to test the agreement. Spearman correlation was performed to evaluate the relevance. The receiver operating characteristic curve was used to analyze the diagnostic efficacy of UPCR.

RESULTS

Bland-Altman analysis showed there was an excellent agreement between UPCR and 24hUP in each group. Correlations between UPCR and 24hUP were strong in 356 children (r = 0.869) and in the non-nephrotic-range proteinuria group (r = 0.806), but moderate in nephrotic-range proteinuria group (r = 0.586). With the increase of nephrotic-range proteinuria, the correlations between UPCR and 24hUP were decreased further, however, after UPCR was adjusted by 24-h urine creatinine (24hUCr), the correlation coefficient was improved (r = 0.682). In three subgroups with nephrotic-range proteinuria, high correlation coefficient (r = 0.731) was observed in HSPN, but not in LN (r = 0.552) and PNS (r = 0.563). The sensitivity and specificity of UPCR for diagnosing nephrotic-range proteinuria were 89.9 % and 92.2%.

CONCLUSIONS

UPCR is competent in evaluating proteinuria. The degree of proteinuria, 24hUCr and the underlying pathological types of renal disease may be the important influencing factors in the correlation between UPCR and 24hUP in children with nephrotic-range proteinuria.

Correlation between spot and 24h proteinuria: Derivation and validation of equation to estimate daily proteinuria

Daily urine protein (UP) loss is a cumbersome but important measurement to guide diagnosis and treatment of renal disease. Spot urine protein-creatinine ratio (UPCR) can been applied to estimate daily proteinuria. However, the correlations between spot and 24h proteinuria remain controversial. In this cross-sectional study, simultaneous collection of 24h and spot urines were performed from 1,039 (derivation cohort) and 204 CKD patients (validation cohort) of Chang Gung Memorial Hospital, from 2007 to 2017. The correlations between spot UPCR and 24h proteinuria were compared. The mean age of patients of derivation and validation cohort was 63 and 55 years and the mean estimated glomerular filtration rate was 62 ± 35 and 59 ± 36 mL/min/m², respectively. The correlation coefficient was 0.819 between UPCR and 24hUP. Prediction equation was derived as: Log₁₀24hUP (g) = 0.814 x Log₁₀UPCR (mg/mg) + 0.110 x Gender– 0.004 x Age + 0.004 x Body weight (kg) + 0.002 x CKD stage coefficient– 0.018, where CKD stage coefficient: CKD stage G1 = 1, G2 = 2, G3a = 3.1, G3b = 3.2, G4 = 4, G5 = 5. Correlation coefficient between measured and predicted 24hUP among derivation group and validation group is 0.866 and 0.915, respectively. However, the agreement of spot and daily estimates was less pronounced with proteinuria > 3g than lower values in Bland-Altman analysis. Spot UPCR can accurately predict 24hUP in patients with daily proteinuria below 3g. The development of this equation may facilitate estimation of 24hUP in the clinical practice.

Clinical utility of spot urine protein-to-creatinine ratio modified by estimated daily creatinine excretion in children

BACKGROUND

The spot urine protein-to-creatinine ratio (UPCR) is widely used to predict 24-h urine protein (24-h UP) excretion. In patients with low daily urine creatinine excretion (UCr), however, the UPCR may overestimate 24-h UP. The aim of this study was to predict 24-h UP using UPCR adjusted by estimated 24-h UCr in children.

METHODS

This study included 442 children whose 24-h UP and spot UPCR were measured concomitantly. Estimated 24-h UCr was calculated using three previously existing equations. We estimated the 24-h UP excretion from UPCR by multiplying the estimated UCr. The results were compared with the measured 24-h UP.

RESULTS

There was a strong correlation between UPCR and 24-h UP (r = 0.801, P < 0.001), and the correlation improved after multiplying the UPCR by the measured UCr (r = 0.847, P < 0.001). Using the estimated UCr rather than the measured UCr, there was high accuracy and strong correlation between the estimated UPCR weighted by the Cockcroft-Gault equation and 24-h UP. Improvement was also observed in the subgroup (proteinuria vs. non-proteinuria) analysis, particularly in the proteinuria group.

CONCLUSIONS

The spot UPCR multiplied by the estimated UCr improved the accuracy of prediction of the 24-h UP in children.

Estimation of the 24-h urinary protein excretion based on the estimated urinary creatinine output

BACKGROUND

The urinary protein/creatinine ratio [Up/Ucr (g/gCr)] has been used in the clinical management of patients with chronic kidney disease (CKD). However, a discrepancy is often noted between the Up/Ucr and 24-h urinary protein excretion [24hUp (g/day)] in patients with extremes of muscle mass. We examined devised a method for precise estimation of the 24-h urinary protein excretion (E-24hUp) based on estimation of 24-h urinary creatinine output (E-24hCr).

METHODS

Three parameters, spot Up/Ucr, 24hUP and E-24hUp (=Up/Ucr × E-24hCr), were determined in 116 adult patients with CKD. The correlations among the groups were analyzed.

RESULTS

There was a significant correlation between the Up/Ucr and 24hUp (p < 0.001). We divided the patients into three groups according to the 24hUp; the low urinary protein group (<1.0 g/day), the intermediate urinary protein group (1.0-3.5 g/day), and the high urinary protein group (>3.5 g/day). There was a significant correlation between the Up/Ucr and 24hUp in the low (p = 0.04) and high urinary protein (p = 0.01) groups, whereas the correlation coefficient was lower in the intermediate urinary protein (p = 0.07) group. Thus, we found a significant correlation between 24hUp and E-24hUp in the study population overall (p < 0.001), in the low (p = 0.01), in the intermediate (p < 0.001), and in the high urinary protein group (p < 0.001).

CONCLUSION

We conclude that a poor correlation exists between the Up/Ucr and 24hUp in patients with intermediate urinary protein excretion levels. The recommended parameter for monitoring proteinuria in such patients may be the E-24hUp, which is calculated using the E-24hCr.