Optimal cut-off point for protein:creatinine ratio
Published guidelines have suggested using a protein:creatinine ratio (PCR)
cut-off point of 30mg/mmol for diagnosing significant proteinuria. Cote et al
(2008) have demonstrated that this cut-off point is a reasonable rule-out test
for proteinuria of 0.3g/day or more.1At present, PCR is not
employed in the majority of maternity units in the UK. Instead a 24-hour
quantitation of proteinuria is done. While the latter is the gold standard
diagnostic test for significant proteinuria in pre-eclampsia, many women are
still admitted to hospital to have this done. This has substantial resource and
economic implications and poses the added problems of incomplete collection and
poor timing of return of specimens for analysis.2 We therefore agree
with the authors that the use of protein:creatinine ratios may facilitate the
diagnosis of new significant proteinuria by enabling results the same day the
patient first attends the hospital.
However based on a small sample of
women in our local hospital we advocate a protein: creatinine ratio cut-off
level of ≥20 mg/mmol for instigating 24 hour collection. Our small data set
comparing cut-off values of 30mg/mmol to20 mg/mmol are shown in the table below.
Although a cut-off value of 30mg/mmol appears to
give better likelihood ratios for significant proteinuria, 20mg/mmol has higher
sensitivity although consequentially, a lower specificity. Employing the latter
threshold, the additional resource implications of performing a few more 24
hour urine protein estimations may be obviated by the potential risk of missing
women with established pre-eclampsia who may be sent home at the risk of
complications in an unattended setting. It is on this basis that we recommend
using 20mg/mmol as cut-off threshold for performing 24-hour collections. However
we accept that further studies from both clinical and economic standpoints are
required to determine the best cut-off values for routine clinical practice
Cote et al (2008)
Jivraj et al (2008)
Jivraj et al (2008)
Cut off point
30mg/mmol
30mg/mmol
20mg/mmol
n=1214
n=17
n=17
Sensitivity
83.6%
82%
91%
Specificity
76.3%
100%
67%
LR+
3.53
infinity
2.7
LR-
0.21
0.18
0.14
References:
1. Cote A-M, Brown MA, Lam E et al. Diagnostic accuracy of urinary spot
protein:creatinine ratio for proteinuria in hypertensive pregnant women:
systematic
Rapid Response:
Optimal cut-off point for protein:creatinine ratio
Published guidelines have suggested using a protein:creatinine ratio (PCR) cut-off point of 30mg/mmol for diagnosing significant proteinuria. Cote et al (2008) have demonstrated that this cut-off point is a reasonable rule-out test for proteinuria of 0.3g/day or more.1At present, PCR is not employed in the majority of maternity units in the UK. Instead a 24-hour quantitation of proteinuria is done. While the latter is the gold standard diagnostic test for significant proteinuria in pre-eclampsia, many women are still admitted to hospital to have this done. This has substantial resource and economic implications and poses the added problems of incomplete collection and poor timing of return of specimens for analysis.2 We therefore agree with the authors that the use of protein:creatinine ratios may facilitate the diagnosis of new significant proteinuria by enabling results the same day the patient first attends the hospital.
However based on a small sample of women in our local hospital we advocate a protein: creatinine ratio cut-off level of ≥20 mg/mmol for instigating 24 hour collection. Our small data set comparing cut-off values of 30mg/mmol to20 mg/mmol are shown in the table below. Although a cut-off value of 30mg/mmol appears to give better likelihood ratios for significant proteinuria, 20mg/mmol has higher sensitivity although consequentially, a lower specificity. Employing the latter threshold, the additional resource implications of performing a few more 24 hour urine protein estimations may be obviated by the potential risk of missing women with established pre-eclampsia who may be sent home at the risk of complications in an unattended setting. It is on this basis that we recommend using 20mg/mmol as cut-off threshold for performing 24-hour collections. However we accept that further studies from both clinical and economic standpoints are required to determine the best cut-off values for routine clinical practice
Cote et al (2008)
Jivraj et al (2008)
Jivraj et al (2008)
Cut off point
30mg/mmol
30mg/mmol
20mg/mmol
n=1214
n=17
n=17
Sensitivity
83.6%
82%
91%
Specificity
76.3%
100%
67%
LR+
3.53
infinity
2.7
LR-
0.21
0.18
0.14
References:
1. Cote A-M, Brown MA, Lam E et al. Diagnostic accuracy of urinary spot
protein:creatinine ratio for proteinuria in hypertensive pregnant women: systematic
review. BMJ 2008;336:1003-1006
2. Kyle, P.M., Fielder, J.N., Pullar, B., Horwood, L.J., and Moore, M.P.
Comparison of methods to identify significant proteinuria in pregnancy in the
outpatient setting. BJOG 2008;115:523-527.
Shehnaaz Jivraj
SpR Obstetrics & Gynaecology
Dilly Anumba
Consultant Obstetrician and Subsepcialist Feto-Maternal Medicine
Competing interests: None declared
Competing interests: No competing interests