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Obstetrics & Gynecology 1999;93:780-782
© 1999 by The American College of Obstetricians and Gynecologists
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ORIGINAL RESEARCH

Peritoneal Fluid Urea Nitrogen and Creatinine Reference Values

KELLY J. MANAHAN, MD and JAMES FANNING, DO

From the Division of Gynecologic Oncology, Department of Obstetrics and Gynecology, Medical College of Ohio, Toledo, Ohio.

Address reprint requests to: James Fanning, DO Department of Obstetrics and Gynecology Richard D. Ruppert Health Center Medical College of Ohio 3120 Glendale Avenue Toledo, OH 43614-5809


   Abstract
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Abstract
Materials and Methods
 Results
 Discussion
 References
 
Objective: To evaluate urea nitrogen and creatinine levels in peritoneal fluid.

Methods: We prospectively evaluated 20 consecutive women having radical hysterectomy with lymphadenectomy. On postoperative days 2 and 3, serum, urine, and peritoneal fluid samples were tested for urea nitrogen and creatinine. Using power analysis we calculated an adequate sample size to be 16 patients.

Results: The mean urea nitrogen was 11 mg/dL in serum, 11 mg/dL in peritoneal fluid, and 469 mg/dL in urine. The mean creatinine was .9 mg/dL in serum, 1.0 mg/dL in peritoneal fluid, and 141 mg/dL in urine. Urea nitrogen and creatinine values in peritoneal fluid and serum were essentially identical. Urine urea nitrogen and creatinine values were significantly greater than serum and peritoneal values (47 to 157 times greater) (P < .011). On postoperative days 2 and 3, serial levels of serum, peritoneal fluid, and urine urea nitrogen and creatinine in the same subject showed no significant variation (P ranging from .19 to .31).

Conclusion: Normal reference values of urea nitrogen and creatinine in peritoneal fluid are equivalent to serum values and significantly less than urine levels.

A common problem after radical hysterectomy with lymphadenectomy is increased peritoneal drainage (more than 500 mL in 24 hours) with decreased urinary output (less than 1000 mL in 24 hours). The major differential diagnosis is between increased postoperative peritoneal drainage and urinary fistula. In a study of 968 radical hysterectomies for cervical cancer, Averette et al1 reported a 4.4% incidence of urinary fistula. Measurements of urea nitrogen and creatinine levels in peritoneal fluid have been compared to levels in serum, and peritoneal fluid urea nitrogen and creatinine levels similar to serum levels are believed to be diagnostic of increased peritoneal drainage rather than urinary fistula. Although that test is used, we were unable to identify reference values for urea nitrogen or creatinine in postoperative peritoneal fluid or urine through a search of MEDLINE from 1966–1998, a laboratory manual,2 the New England Journal of Medicine,3 and direct consultation with the pathologist in charge of laboratory medicine at the Medical College of Ohio.

The purposes of this study were to measure peritoneal fluid urea nitrogen and creatinine in women who had radical hysterectomy with lymphadenectomy and to determine the correlation and variability of urea nitrogen and creatinine levels in serum, peritoneal fluid, and urine.


   Materials and Methods
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Abstract
 Materials and Methods
Results
 Discussion
 References
 
Twenty consecutive women who had Rutledge class III radical hysterectomy4 with bilateral pelvic and periaortic lymphadenectomy were entered in this prospective trial during 1 year. No potential subjects were excluded. The surgical stapling technique of radical hysterectomy, as described by Fanning et al,5,6 was done on all subjects. An intraperitoneal suction drain was placed in the deepest part of the pelvis. The drainage catheter exited the skin through a site separate from the surgical incision and was attached to a closed-suction adapter.

On postoperative days 2 and 3, 10-mL samples of blood, urine, and peritoneal fluid were collected simultaneously once daily from each subject, placed in redtop chemistry tubes, and sent to the laboratory for measurement of urea nitrogen and creatinine levels. All samples were processed by routine enzymatic and photometric analysis using a LX20 analyzer (Beckman Coulter, Inc., Fullerton, CA).

Investigational Review Board approval was given for this study, and informed consent was obtained from each subject. Paired Student t test was used to compare values of urea nitrogen and creatinine in serum, peritoneal fluid, and urine and to compare intrasubject serial values measured on postoperative days 2 and 3. Correlation coefficients were also calculated. With a desired level of significance of P = .05, a power of .80, and a doubling of urea nitrogen and creatinine considered medically significant, a necessary sample size of 16 patients was calculated.


   Results
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Abstract
 Materials and Methods
 Results
Discussion
 References
 
The median age of subjects was 47 years (range 22–63 years). Seventeen women had cervical carcinoma and three had endometrial carcinoma with gross cervical involvement. All women had normal preoperative serum urea nitrogen and creatinine levels. None developed clinical evidence of urinary fistulas, evidenced by prolonged, excessive peritoneal drainage or excessive vaginal discharge. The mean urea nitrogen level in serum was 11 mg/dL (range 5–17 mg/dL). The mean creatinine level in serum was 0.9 mg/dL (range 0.5–1.8 mg/dL). The mean urea nitrogen level in peritoneal fluid was 10 mg/dL (range 3–27 mg/dL). The mean creatinine level in peritoneal fluid was 0.9 mg/dL (range 0.5–2.0 mg/dL). The mean urea nitrogen level in urine was 469 mg/dL (range 106–918 mg/dL). The mean creatinine level in urine was 141 mg/dL (range 50–290 mg/dL). Among individual subjects, urea nitrogen in peritoneal fluid exceeded that in serum in only two cases, both of which had urea nitrogen level in peritoneal fluid of 14 mg/dL and in serum of 12 mg/dL. Peritoneal fluid creatinine level exceeded serum creatinine in only three cases, in which peritoneal fluid values were .8, .8, and 1.1 mg/dL and serum creatinine values were .7, .6, and .7 mg/dL, respectively.

Table 1Go gives the intrasubject values of urea nitrogen and creatinine in serum, peritoneal fluid, and urine measured on postoperative days 2 and 3. Intrasubject serial serum values of urea nitrogen and creatinine showed narrow ranges, small standard deviations (SDs) (P = .25 and .29, respectively), and good correlations. Intrasubject serial peritoneal fluid values of urea nitrogen and creatinine had narrow ranges, small SDs (P = .19 and .27, respectively), and excellent correlations. Intrasubject serial urine values of urea nitrogen and creatinine had larger ranges and SDs (P = .31 and .22, respectively) and fair correlations.


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  		Table 1. Intrapatient Variability of Serum, Peritoneal Fluid, and Urine Levels of Urea Nitrogen and Creatinine
 
Table 2Go compares urea nitrogen and creatinine values in serum, peritoneal fluid, and urine samples. Urea nitrogen levels in serum and peritoneal fluid were nearly identical (P = .94). Urine urea nitrogen mean values were markedly different (47 times greater) from serum and peritoneal fluid values (P < .001). Urea nitrogen levels in serum and peritoneal fluid had excellent correlations, whereas urine and peritoneal levels had poor correlations. Serum and peritoneal fluid values of creatinine were virtually identical (P = .98) and creatinine mean value in urine was markedly different (157 times greater) from that in serum and peritoneal fluid (P < .001). Serum and peritoneal fluid creatinine levels had excellent correlation, whereas urine and peritoneal fluid levels showed poor correlation.


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  		Table 2. Comparison of Serum, Peritoneal Fluid, and Urine Levels of Urea Nitrogen and Creatinine
 

   Discussion
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Abstract
 Materials and Methods
 Results
 Discussion
References
 
We found that postoperative serial peritoneal fluid levels of urea nitrogen and creatinine had limited intrasubject variance, were identical to serum values, and were significantly less than urine values. Although we were unable to identify reference values of urea nitrogen and creatinine in peritoneal fluid, we believe our data show that reference values are equivalent to serum values. Although we logically assumed that reference values of urea nitrogen and creatinine in peritoneal fluid would be equivalent to serum values because physiologic peritoneal fluid is a plasma filtrate, we believe that reference values must be scientifically established because in the present era of scientific medicine, "medicine practiced by intuition or anecdotal experience, which may have been laudable at one time in medical history, is now condemned because it cannot withstand the scrutiny of scientific methods."7

We previously reported that the only clinically significant difference between the surgical stapling technique and traditional technique of radical hysterectomy is decreased operation time and blood loss, so we do not believe that values of peritoneal fluid urea nitrogen and creatinine are influenced by the type of hysterectomy done.5,6

We established that levels of urea nitrogen and creatinine in peritoneal fluid and serum were identical and that urine values were significantly greater (47 to 157 times), when excessive peritoneal fluid was found after radical hysterectomy; therefore, we propose that the measurement of urea nitrogen and creatinine in peritoneal fluid might be a valid initial test to determine intraperitoneal urinary leakage. If peritoneal fluid values were equal to serum values, then one might follow that woman conservatively. Conversely, if peritoneal fluid values were higher than serum values one might proceed with more extensive radiologic evaluation to detect possible urinary fistula. There appear to be several situations where measurement of urea nitrogen and creatinine in peritoneal fluid can be clinically beneficial. Excessive postoperative peritoneal fluid, diagnosed by increased suction catheter output or development of pelvic ascites, might occur after gynecologic procedures other than radical hysterectomy, such as surgery for endometriosis, pelvic inflammatory disease, large pelvic masses, or after urogynecologic procedures. Urea nitrogen and creatinine levels in peritoneal fluid can be collected from excessive postoperative peritoneal fluid to determine intraperitoneal urinary leakage. Measurement of peritoneal fluid urea nitrogen and creatinine can also identify intraperitoneal urine leakage after trauma. In a study on calves, peritoneal fluid levels of creatinine increased 18 times after traumatic urinary bladder rupture.8 In cases of excessive postoperative suprapubic incisional drainage, measurement of urea nitrogen and creatinine levels might help differentiate urinary leakage from impending incisional dehiscence. Excessive postoperative vaginal drainage might be evaluated by urea nitrogen and creatinine levels to help diagnose postoperative urinary fistulas.


   Footnotes
 
Presented at the 29th Annual Meeting of the Society of Gynecologic Oncology, Orlando, Florida, February, 1998.

PII S0029-7844(98)00516-X

Received August 5, 1998. Received in revised form October 16, 1998. Accepted November 5, 1998.


   References
Top
Abstract
 Materials and Methods
 Results
 Discussion
 References
 
1. Averette HE, Nguyen HN, Donato DM, Penalver MA, Sevin BU, Estape R, et al. Radical hysterectomy for invasive cervical cancer: A 25-year prospective experience with the Miami technique. Cancer 1993;71:1422–37.[Medline]

2. Henry JB. Clinical diagnosis and management by laboratory methods, 18th ed. Philadelphia, Pennsylvania: W.B. Saunders, 1991:469.

3. Kratz A, Lewandrowski KB. Case records of the Massachusetts General Hospital. Weekly clinopathological exercises. Normal reference laboratory values. N Engl J Med 1998;339:1063–72.[Free Full Text]

4. Piver MS, Rutledge F, Smith JP. Five classes of extended hysterectomy for women with cervical cancer. Obstet Gynecol 1974;44:265–72.[Abstract/Free Full Text]

5. Fanning J, Hilgers RD, Palabrica C. Surgical stapling technique for radical hysterectomy. Gynecol Oncol 1994;55:179–84.[Medline]

6. Fanning J, Hilgers RD, Murray KP. Surgical stapling technique for radical hysterectomy. J Pelvic Surg 1995;1;73–8.

7. Council on Resident Education in Obstetrics and Gynecology. Educational Objectives. Core curriculum in obstetrics and gynecology. 5th ed. Washington DC: Council on Resident Education in Obstetrics and Gynecology, 1996:1.

8. Wilson DG, MacWilliams PS. An evaluation of the clinical pathologic findings in experimentally induced urinary bladder rupture in pre-ruminant calves. Can J Vet Res 1998;62:140–3.[Medline]





This Article
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