OB-GYN-L Messages for March, 2002: Re: Protein creatinine ratio

Re: Protein creatinine ratio

From:

ainsron@msn.com

Thu Mar 14 21:18:56 2002

Clinical Nephrology, Vol. 55, No. 6/2001 (436-447)

Cost-benefit analysis and prediction of 24-hour proteinuria from the spot urine protein-creatinine ratio V.C. Chitalia1, J. Kothari2, E.J. Wells3, J.H. Livesey4, R.A. Robson1, M. Searle1 and K.L. Lynn1 1Department of Nephrology, Christchurch Hospital, Christchurch, New Zealand, 2Department of Medicine, Division of Nephrology, Seth G.S. Medical College and K.E.M. Hospital, University of Bombay, India, 3Department of Public Health, Christchurch School of Medicine, and 4Department of Endocrinology, Christchurch Hospital, Christchurch, New Zealand Aim: A prospective cross-sectional study was performed on 170 patients with various glomerular diseases to study the accuracy of predicting 24-hour proteinuria from the spot urine protein-creatinine ratio (Up/Uc). A cost-benefit analysis was performed for the New Zealand health economic system to obtain the best cut-off values for proteinuria. Subjects, methods and results: Two spot urine samples (Up/Uc1 and Up/Uc2) were collected on the same day as the collection of a 24-hour urine. A randomly chosen subsample of 50 patients provided a second set of urine samples. The correlation and precision of agreement between the two methods were examined. The predictive intervals were calculated for derived 24-hour proteinuria. The level of agreement was evaluated by the Bland-Altman method and concordance analysis. The limits of agreement were evaluated against the clinical limits of agreement. A cost-benefit analysis (CBA) was performed to obtain the optimum operating points on receiver operating characteristic (ROC) curves for the best decision threshold. Correlations of r = 0.97 and 0.99 were observed between Up/Uc1, Up/Uc2 and 24-hour proteinuria, respectively. The 95% predictive intervals were wide. A high concordance correlation coefficient was obtained. The most of the differences between the two methods fell within the clinical limits of agreement. The Up/Uc1 of 0.26 and 3.20 represent the best thresholds to detect normal and nephrotic proteinuria, respectively. Conclusions: Despite wide confidence intervals, a good correlation and precision of agreement were demonstrated between the two methods across the whole range of proteinuria, regardless of the level of renal function. The difference between the two methods was less than the biological variability in the protein excretion and its measurement, enabling the methods to be used interchangeably. The optimum thresholds for abnormal and nephrotic range proteinuria were obtained.

At Thu, 14 Mar 2002, Montgomery, Lynn MD wrote: >
>This is why I ask. Abstract from this years SMFM meeting:
>
> "Prospective prediction of 24 hour proteinuria by spot protein
> creatinine ratio. Binno, et.al.
>
> Objective: The degree of proteinuria is frequently assessed
> in obstetric patients with preeclampsia, diabetes and other
> medical complications. The gold standard has been a 24 hour
> collection of urine. Obviously collecting urine for 24 hours
> is cumbersome and may frequently result in erroneous results
> secondary to incomplete collections. In the non-obstetric
> population, the spot Protein Creatinine Ratio (PCR) is used
> to assess the degree of proteinuria. This study examined the
> prospective prediction of the 24 hour proteinuria using the
> spot PCR in obstetric patients.
>
> Study Design: One hundred-twenty antepartum patients with a
> variety of medical indications, were asked to obtain a 24 hour
> urine specimen at home, on the day prior to their clinic visit.
> At their clinic visit they were asked to obtain a single urine
> sample for the spot PCR. The 24 hour urine protein content was
> measured in the laboratory. The spot PCR was used to predict
> the 24 hour urine protein content and the correlation between
> the measured 24 hour urine protein and the predicted 24 hour
> urine protein is presented.
>
> Results: Ninety five patients completed the urine collections
> for data analysis. The Peason coefficient for the correlation
> between the measured and the predicted 24 hour urine protein
> was 0.903, with R-squared value of 0.815 and a P < .001. The
> 24 hour proteinuria < 300mg was accurately predicted in 63 out
> of 68 patients, proteinuria between 300mg and 5 grams was
> accurately predicted in 20 out of 23 patients and proteinuria
> > 5 grams was accurately predicted in all remaining cases.
>
> Conclusion: These results confirm that the spot Protein Creatinine
> Ratio is a highly reliable assessment for the degree of proteinuria
> in the pregnant population. Using PCR will enhance patient care
> and will be cost saving as well."
>
>So if it can't be done, how did they do it?
>Lynn
>
>-----Original Message-----
>From: ob-gyn-l@obgyn.net [mailto:ob-gyn-l@obgyn.net]On Behalf Of Steve &
>Eryl Raymond
>Sent: Thursday, March 14, 2002 10:31 AM
>To: Multiple recipients of list OB-GYN-L
>Subject: Re: Protein creatinine ratio
>
>Can't be done. Total urinary excretion varies diurnally.
>stray
>
>"Montgomery, Lynn MD" wrote:
>
>> Hey y'all,
>> This may be a stupid question, but does anybody know how to convert a spot
>> protein creatinine ratio into an equivalent total 24 hour protein amount?
>> Lynn
>>
>> Lynn D. Montgomery, M.D.
>> Director, Maternal-Fetal Medicine
>> Rocky Mountain Perinatal Center
>> 2825 Fort Missoula Rd, Suite 130
>> Missoula, Montana, 59804
>> 406-327-4094
>> fax: 406-327-4154
>> e-mail: lmontgomery@communitymed.org
>> website: http://www.communitymed.org/rmpc/
>
>--
>
>Dr.S.H. Raymond
>Head of Department of O & G
>Empangeni Hospital
>South Africa 3880
>Phone: (+27) 35-7721111
>Fax: (+27) 35-7922596
>

-- Ronald E. Ainsworth, MD

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