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ORIGINAL ARTICLE
Year : 2015  |  Volume : 28  |  Issue : 2  |  Page : 406-410

Clinical significance of saliva urea and creatinine levels in patients with chronic kidney disease


1 Department of Internal Medicine, Faculty of Medicine, Menoufiya University, Menoufiya, Egypt
2 Department of Clinical Pathology, Faculty of Medicine, Menoufiya University, Menoufiya, Egypt

Date of Submission10-Mar-2014
Date of Acceptance27-Jun-2014
Date of Web Publication31-Aug-2015

Correspondence Address:
Basem Said Abd Al-Baky Mashal
Shebin El-kom, El Menoufiya 32511
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1110-2098.163893

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  Abstract 

Objectives
This study was carried out to explore the changes and clinical significance of urea and creatinine in saliva in patients with chronic kidney disease (CKD) and provide a noninvasive, quick, accurate, and reliable test for diagnosing kidney disease.
Background
Monitoring of markers in saliva instead of serum is advantageous because saliva collection is a noninvasive, simple, and inexpensive approach. Measurement of biomarkers in saliva may be an effective alternative method for monitoring the effectiveness of hemodialysis.
Patients and methods
Urea and Cr in the saliva and serum were collected from both healthy individuals and CKD patients and measured with a biochemical analyzer. Fifty individuals participated in this study, divided into 40 patients with CKD and 10 apparent healthy controls.
Results
The concentrations of urea and Cr in both saliva and serum were positively correlated in healthy individuals and CKD patients. The levels of saliva urea and Cr in CKD patients were significantly higher than those of healthy individuals (P < 0.05). Saliva urea and Cr concentrations of middle-stage and late-stage CKD patients were higher than those of healthy people and early-stage CKD patients (P < 0.05). Areas under the curve of the receiver operating characteristic of saliva creatinine and urea and serum creatinine and urea were, respectively, 0.876, 0.796, 0.942, and 0.922 and specificity was 80, 80, 90, and 80, respectively.
Conclusion
The levels of urea and Cr in saliva and serum are closely related. The concentration of saliva urea and Cr can reflect renal damage, monitor the kidney function of CKD patients, and help in the diagnosis of middle-stage and late-stage CKD. It is a simple, noninvasive, and quick method.

Keywords: chronic kidney disease, creatinine, saliva, urea


How to cite this article:
Bader RS, Kora MA, El-Shalakany AH, Mashal BS. Clinical significance of saliva urea and creatinine levels in patients with chronic kidney disease. Menoufia Med J 2015;28:406-10

How to cite this URL:
Bader RS, Kora MA, El-Shalakany AH, Mashal BS. Clinical significance of saliva urea and creatinine levels in patients with chronic kidney disease. Menoufia Med J [serial online] 2015 [cited 2020 Feb 27];28:406-10. Available from: http://www.mmj.eg.net/text.asp?2015/28/2/406/163893


  Introduction Top


Saliva is an exocrine secretion produced by three pairs of major glands and numerous minor glands located throughout the oral mucosa. In humans, saliva is the first step in digesting food. It maintains the mineralization of the teeth and moisturizes and protects the oral mucosa. It is necessary for speech and swallowing of food. It is also essential for protection against serious systemic pathogens. A little known fact about saliva, however, is that it is a unique medium that can be used as a diagnostic fluid [1] .

Saliva is a diagnostic fluid for scientists and clinical researchers. It is easy to collect and noninvasive and can be collected repeatedly without discomfort to the patient. It can be obtained in a variety of settings, ranging from health fairs to roadside law enforcement procedures [2] .

The late Dr Irwin Mandel reported that salivary diagnostics have origins in ancient China through the use of the rice test. A person accused of a crime was given a mouthful of dry rice. If guilty, anxiety inhibited salivation so that the defendant could not form an adequate bolus for chewing and swallowing [3] .

Saliva has been considered a mirror of the human body able to reflect an individual's emotional, hormonal, immunologic, and neurological status. Saliva is also an indicator of nutritional and metabolic influence and of tissue fluid levels of natural substances, as well as of molecules introduced for therapeutic or recreational purposes [4] .

Serum urea and creatinine correlate very well with salivary urea, which can be used as a low-cost, easily accessible, and noninvasive diagnostic method for screening patients in early stages of kidney disease, especially in developing countries where resources are limited, giving the possibility of establishing a secondary prevention program [5] .


  Patients and methods Top


Forty patients with chronic kidney disease (CKD) participated in the present study. Their ages ranged from 23 to 74 years with a mean age of 47.6 ± 12.14 years. Patients were selected from among those attending the Medical Hospital Complex, Health Insurance, Tanta.

They were divided into two groups:

Group I: This group comprised CKD patients and was divided into two subgroups:

Group Ia: This subgroup consisted of 30 end-stage renal disease (ESRD) patients on regular hemodialysis and comprised 20 male and 10 female patients. Their ages ranged from 31 to 74 years with a mean of 48 ± 11.42 years.

Group Ib: This subgroup consisted of 10 CKD patients in different stages except stage 5 and comprised eight male and two female patients. Their ages ranged from 36 to 73 years with a mean of 53 ± 11.54 years.

In addition, 10 apparently healthy individuals were included as a control group (group II), comprising eight male and two female patients. Their ages ranged from 23 to 64 years with a mean of 40.7 ± 12.56 years.

We excluded patients with acute kidney injury or hepatorenal syndrome.

All patients and controls were subjected to the following:

(1) Full history taking : It included present and past history.

(2) Thorough clinical examination:

(a) General examination.

(b) Abdominal examination.

(c) Chest examination.

(3) Laboratory investigations:

(a) Routine laboratory investigations:

(i) Complete blood count.

(ii) Kidney function tests - for example, serum creatinine and blood urea.

(iii) Serum calcium.

(iv) Serum intact parathyroid hormone.

(v) Creatinine clearance by 24 h urine collection and by Schwartz formula.

(3) Special laboratory investigations:

(a) Salivary urea and creatinine.

Sample collection

All samples were collected in the early morning.

Collecting 5 ml of saliva is simple and gives a copious amount for the saliva test. Unstimulated whole saliva can be collected with either passive drooling or by spitting directly into a plastic collector vial and after collection kept on ice and frozen to analyze saliva urea and creatinine.

At the same time 3-5 ml of venous blood was drawn by means of sterile vein puncture and transferred into a dry sterile centrifuge tube. The whole blood was allowed to clot at room temperature and then centrifuged for 10 min at 4000 rpm. The clear supernatant serum was separated from the clot and kept frozen at −20°C until analysis for serum urea and creatinine.

Estimation of creatinine in serum and saliva

Principle

In the presence of a strong base such as NAOH, picrate reacts with creatinine to form a red chromophore. The rate of increasing absorbance at 510 nm due to the formation of this chromophore is directly proportional to the creatinine concentration in the sample and is measured using a bichromatic (510, 600 nm) rate technique.

Red chromophore → Creatinine + Picrate NaOH(absorbs at 210 nm)

Reagents:



Reagent preparation

All reagents were liquid and ready to use.

Reagent stability

All reagents were stable until the expiration date stated on the label when stored at 2-8°C.

Specimen collection and handling: The recommended specimen types were serum, plasma, and saliva.

  1. Serum and plasma can be collected using recommended procedures for collection of diagnostic blood specimens by means of venipuncture.
  2. Complete clot formation should take place before centrifugation. Serum or plasma should be physically separated from cells with a maximum limit of 2 h from the time of collection. Specimens should be free of particulate matter.
  3. Saliva can be collected by either passive drooling or by spitting directly into a plastic collector vial and after collection kept on ice and frozen until analysis.
Procedure

Sampling, reagent delivery, mixing, processing, and printing of results were performed automatically using the Dimention system.

Results

The instrument automatically calculates and prints the concentration of creatinine in mg/dl (μmol/l).

Expected values

Serum

Male patients: 0.8-1.3 mg/dl (71-115 μmol/l).

Female patients: 0.6-1.0 mg/dl (53-88 μmol/l).

This serum reference population comprised the following: 71 male patients, aged 19-72 years and 129 female patients, aged 19-72 years.

Saliva

The salivary level of creatinine shares a close relationship with serum levels, with an average concentration 10 times less than that of serum.

Estimation of urea in serum and saliva

Principle

Urease specifically hydrolyzes urea to form ammonia and carbon dioxide.

Ammonia is used by the enzyme glutamate dehydrogenase (GLDH) to reductively aminate a-ketoglutarate (α-KG), with simultaneous oxidation of reduced nicotinamide-adenine dinucleotide (NADH). The change in absorbance at 340 nm due to the disappearance of NADH is directly proportional to the blood urea nitrogen concentration in the sample and is measured using a bichromatic (340, 383 nm) rate technique.

Reagents:



Reagent preparation

Hydrating, mixing, and diluting are automatically performed by the instrument.

Reagent stability

All reagents are stable until the expiration date stated on the label when stored at 2-8°C.

Specimen collection and handling

  1. Serum and plasma can be collected using recommended procedures for collection of diagnostic blood specimens by means of venipuncture.
  2. Saliva can be collected by either passive drooling or by spitting directly into a plastic collector vial and after collection kept on ice and frozen until analysis
  3. Procedure
Sampling, reagent delivery, mixing, processing, and printing of results are automatically performed by the Dimention system.

Results

The instrument automatically calculates and prints the concentration of creatinine in mg/dl (μmol/l).

Expected values

Serum

The expected reference value for serum was 7-18 mg/dl (2.5-6.4 mmol/l).

This reference population comprised the following: 110 male patients, aged 20-65 years and 110 female patients, aged 20-65 years.

Saliva

Six random saliva samples were clarified, diluted, and tested in the kit. The saliva urea values ranged from 39 to 66 mg/dl, with an average concentration of 52.2 mg/dl.


  Results Top


The study was carried out on 40 CKD patients (group I) who were divided into subgroup Ia (consisting of 30 ESRD patients on regular hemodialysis) and subgroup Ib (consisting of 10 CKD patients in different stages except stage 5). In addition, 10 apparent healthy individuals served as the control group (group II).

The results showed a nonsignificant difference among the studied groups regarding age and sex (P > 0.05). There was significant difference among the studied groups regarding serum creatinine, serum urea, saliva creatinine, and saliva urea (P < 0.05). The levels of saliva urea and creatinine in CKD patients were significantly higher than those of healthy people (P < 0.05).

There was significant positive correlation (P < 0.05) between serum creatinine and saliva creatinine in the healthy group, CKD patients, and ESRD patients (r = 0.83, 0.58, and 0.89, respectively) [Table 1]. There was also a positive correlation (P < 0.05) between serum urea and saliva urea in the healthy group, CKD patients, and ESRD patients (r = 0.89, 0.99, and 0.98, respectively).
Table 1 Correlation between serum creatinine and saliva creatinine in the chronic kidney disease group

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The sensitivity, specificity, and area under the curve (AUC) of saliva urea and creatinine are comparable to those of blood urea and serum creatinine [Table 2].
Table 2 Sensitivity, specificity, and area under the curve of saliva urea and creatinine and serum urea and creatinine

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  Discussion Top


The worldwide increase in the number of patients with CKD and consequent ESRD necessitating renal replacement therapy and attendant cardiovascular disease is threatening to reach epidemic proportions over the next decade, and only a small number of countries have robust economies to meet the challenges posed [6] .

A change in the global approach to CKD from treatment of ESRD to much more aggressive primary and secondary prevention is therefore imperative in developing countries such as Egypt [7] .

Medical diagnosis currently depends heavily on information gathered from blood tests, urine tests, biopsies, and physical examination. Saliva remains a largely untapped source of medical information that can enhance diagnostic accuracy while saving the patient from some of the discomfort associated with a blood test or other more invasive procedures. Many constituents of the blood make their way into saliva, thus making saliva an indicator of the current state of the blood and of the rest of the body. Many biomarkers, or substances used as indicators of biological states, can be readily found in saliva [8] .

Any diagnostic tool that can detect kidney disease in its early stages can save lives. The kidney's main responsibility is cleaning the blood of waste. Because urine forms mainly through passive diffusion, just like saliva, many components of the blood exchanged at the kidney are also exchanged at the salivary glands [9] .

A wide variety of symptoms indicate the need for a kidney test, and hence physicians call for such tests quite frequently. Saliva testing can replace the initial blood sampling in these situations. A positive saliva test may lead to more invasive tests, but a negative one can spare the patient and physician this inconvenience.

Analysis of saliva composition may be used as a diagnostic tool for the localization and assessment of various systemic diseases (such as ESRD). Such analysis must be based on a broad understanding of the specific concentrations and origins of the various immunological and biochemical components of saliva [10] .

Blicharz and colleagues suggest that the measurement of biomarkers in saliva may be an effective alternative method for monitoring the effectiveness of hemodialysis. Monitoring of markers in saliva instead of serum is advantageous because saliva collection is a noninvasive, simple, and inexpensive approach with minimal infectious risk that can be performed by the patient with no involvement of medical personnel. Saliva can be tested at home, thus avoiding a visit to the clinic or hospital [11] .

There was significant difference between the studied groups with regard to serum creatinine, serum urea, saliva creatinine, and saliva urea (P < 0.05). The levels of saliva urea and creatinine in CKD patients were significantly higher than those of healthy individuals (P < 0.05).

The present study showed significant positive correlation between serum creatinine and saliva creatinine in the healthy group, in CKD patients, and in ESRD patients (r = 0.83, 0.58, and 0.89, respectively). There was also a positive correlation between serum urea and saliva urea in the healthy group, in CKD patients, and in ESRD patients (r = 0.89, 0.99, and 0.98, respectively).

This study is in agreement with that by Xia et al. [12] who stated that the concentrations of urea, Cr, and UA in both the saliva and the serum were positively correlated in healthy individuals and CKD patients.

The sensitivity, specificity, and AUC of saliva urea and creatinine are comparable to those of blood urea and serum creatinine.


  Conclusion Top


The sensitivity, specificity, and AUC of saliva urea and creatinine are comparable to those of blood urea and serum creatinine. The concentration of saliva urea and Cr can reflect renal damage, monitor kidney function of CKD patients, and help in the diagnosis of middle-stage to late-stage CKD. It is a simple, noninvasive, and quick diagnostic method.


  Acknowledgements Top


Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Aps JKM, Martens LC. Review: the physiology of saliva and transfer of drugs into saliva. Forensic Sci Int 2005; 150 :119-131.  Back to cited text no. 1
    
2.
Giovanni ND, Fucci N, Chiarotti M, et al. Cozart Raiscan system: our experience with saliva test. J Chromat B Analyte Technol Biomed Life 2002; 773 :1-6.  Back to cited text no. 2
    
3.
Elsana S, Sikuler E, Yaari A, et al. HCV antibodies in saliva and urine. J Med Virol 2002; 55 :24-27.  Back to cited text no. 3
    
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Streckfus CF, Bigler LR. Saliva as a diagnostic fluid. Oral Dis 2002; 8 :69-76.  Back to cited text no. 4
    
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Daquan MA. Salivary gland disease. Beijing: Peoples Medical Publishing House; 2002. 119-120.  Back to cited text no. 5
    
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El Nahas AM, Bello AK. Chronic kidney disease. The global challenge. Lancet 2005; 365 :331-340.  Back to cited text no. 6
    
7.
Schoolwerth AC, Engelgau MM, Hostetter TH, et al. Chronic kidney disease: a public health problem that needs a public health action plan. Prev Chronic Dis 2006; 3 :A57.  Back to cited text no. 7
    
8.
Aydin S. A comparison of ghrelin, glucose, alpha-amylase and protein levels in saliva from diabetics J Biochem Mol Biol 2007; 40 :29-35.  Back to cited text no. 8
    
9.
American Association for Clinical Chemistry. Creatinine. Available at: http://www.labtestsonline.org/understanding/analytes/creatinine/test.html. [Last accessed on 2013 Aug].  Back to cited text no. 9
    
10.
Nagler RM, Klein I, Zarzhevsky N, Drigues N, Reznick AZ. Characterization of the differentiated profile of human saliva. Free Radic Biol Med 2002; 32 :51-54.  Back to cited text no. 10
    
11.
Blicharz TM, Rissin DM, Bowden M, Hayman RB, DiCesare C, Bhatia JS, et al. Use of colorimetric test strips for monitoring the effect of hemodialysis on salivary nitrite and uric acid in patients with end-stage renal disease: a proof of principle. Clin Chem 2008; 54 :1473-1480.  Back to cited text no. 11
    
12.
Y Xia, Peng C, Zhou Z, Cheng P, Sun L, Peng Y, et al. Clinical significance of saliva urea, creatinine, and uric acid levels in patients with chronic kidney disease. J Cent South Univ 2012; 75 :32-36.  Back to cited text no. 12
    



 
 
    Tables

  [Table 1], [Table 2]


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