Comparison of Widely Used Biochemical Analytes in the Serum and Saliva Samples of Dialysis Patients

Development of a novel method for the simultaneous detection of trimethylamine N-oxide and creatinine in the saliva of patients with chronic kidney disease - Its utility in saliva as an alternative to blood

Chronic kidney disease (CKD) is associated with increased levels of creatinine and other uremic toxins (UTs), which impaired kidneys cannot filtrate. Typically, CKD is diagnosed by calculating the estimated glomerular filtration rate using serum creatinine or cystatin C levels. In pursuit of more sensitive and reliable biomarkers of kidney dysfunction, scientific attention has turned towards other UTs, such as trimethylamine N-oxide (TMAO), successfully quantified in standard matrices, blood and urine. However, less invasive monitoring of kidney function can be performed using an alternative diagnostic biofluid, saliva, which has been shown to contain clinically relevant concentrations of renal function markers. Accurate quantitative estimation of serum biomarkers using saliva measurements can only be achieved provided that there is a tight saliva-serum correlation for the analyte of interest. Therefore, we aimed to verify the correlation between saliva and serum levels of TMAO in CKD patients using newly developed and validated quantitative liquid chromatography coupled to mass spectrometry (LC-MS) method for simultaneous detection of TMAO, and creatinine - the conventional marker of renal impairment. Secondly, we applied this method to quantify TMAO and creatinine levels in the resting saliva of CKD patients collected with a standardised method involving swab-based collectors. A good linear correlation was obtained between the concentration of creatinine in serum and resting saliva of CKD patients (r = 0.72, p = 0.029) and even better in the case of TMAO (r = 0.81, p = 0.008). The analysed validation criteria were fulfilled. No significant influence of the type of swab in the Salivette® device on creatinine and TMAO concentrations in saliva was detected. Our study indicates that saliva can be successfully used in the non-invasive monitoring of renal failure in CKD by measuring salivary TMAO concentrations.

Salivary changes in chronic kidney disease and in patients undergoing hemodialysis: a systematic review and meta-analysis

OBJECTIVES

This study is aimed at describing changes in salivary flow rate and ionic composition present in the saliva of chronic kidney disease (CKD) patients by assessing the pH, calcium, phosphate, and phosphorus concentrations and comparing them to healthy individuals, along with exploring the influence of hemodialysis on these parameters.

METHODS

The bibliographical search was performed in nine databases to find all types of studies, including observational clinical studies, without restrictions regarding publication year or language. Two reviewers selected the studies, extracted the data, and assessed the risk of bias using JBI tools. Random-effect meta-analysis was performed with the standardized mean difference (SMD) as effect estimate, at a 95% confidence interval.

RESULTS

Thirty-three studies were included in the qualitative synthesis and 31 studies were included in the meta-analysis. Chronic kidney disease patients presented lower salivary flow rate (SMD: - 1.73; 95% CI = - 2.14; - 1.31), higher pH (SMD: 1.57; 95% CI = 1.11; 2.03), and higher phosphorus concentration (SMD: 0.86; 95% CI = 0.63; 1.09) in saliva. Concurrently, salivary flow rate and pH presented significant changes after hemodialysis, with higher salivary flow rate (SMD: 0.53; 95% CI = 0.25; 0.81) and lower pH (SMD: - 0.53; 95% CI = - 0.88; - 0.19) in patients on hemodialysis treatment.

CONCLUSION

Chronic kidney disease patients present reduced salivary flow rate and increased pH and phosphorus concentration in saliva. Hemodialysis can increase the salivary flow rate of these patients.

Effects of hemodialysis treatment on saliva flow rate and saliva composition during in-center maintenance dialysis: a cross-sectional study

Aim

To analyze changes in saliva flow rate and clinical measures from unstimulated whole saliva (UWS) among patients undergoing hemodialysis for end-stage kidney disease (ESKD).

Background

Chronic hemodialysis causes changes in blood chemistry as well as dry mouth, due to removal of excess fluids. UWS is used to examine saliva flow rate as an indicator of mouth dryness. Whether UWS can be used to measure changes in clinical variables following hemodialysis has not been explored.

Design

A cross-sectional quantitative study.

Methods

Patients with ESKD were recruited by purposive sampling (n = 100) between 1 January and 30 June 2015 from a hospital in northern Taiwan. UWS was collected 1-hour pre-dialysis (T1), mid-dialysis (T2), and 1-hour post-dialysis (T3). Saliva flow rate and clinical variables were analyzed.

Results

Saliva flow rate increased significantly from T1 to T3 (Wald χ² = 10.40, p < .01). Changes in saliva from T1 to T3 included decreases in blood urea nitrogen and creatinine (Wald χ² = 97.12, p < .001 and Wald χ² = 36.98, p < .001, respectively). The pH and osmolality also decreased (p < .001 and p < .01, respectively). Changes in electrolytes included decreases in potassium and calcium (Wald χ² = 6.71, p < .05 and Wald χ² = 17.64, p < .01, respectively) and increases in chloride (Wald χ² = 17.64, p < .001).

Conclusion

Our findings demonstrated saliva flow rate and several saliva components were altered during hemodialysis. The total volume of saliva secretion increased following dialysis, which can reduce xerostomia. Therefore, medical personnel could provide interventions of relieving dry mouth symptoms and increasing saliva flow rate before hemodialysis treatment.

Saliva as a tool for monitoring hemodialysis: a systematic review and meta-analysis

This study aimed to assess whether the reductions in serum urea and creatinine levels are different from the reductions in salivary urea and creatinine levels that occur after hemodialysis in chronic renal patients. The systematic review protocol was registered in the PROSPERO database. Eight databases were searched to identify pretest-posttest studies of chronic kidney disease patients undergoing hemodialysis, with no language or year restrictions. The JBI Critical Appraisal Tool was used to assess the risk of bias. Meta-analyses using random-effect models were conducted to compare salivary and serum correlations and to pooled mean and proportion differences from pre- to posthemodialysis urea and creatinine levels by subgroup analysis. The I2 test was used to assess heterogeneity, and a meta-regression was performed to statistically assess correlations and differences in the pooled effects pre- and postdialysis. The Grading of Recommendation, Assessment, Development, and Evaluation (GRADE) was used to assess the certainty of evidence. The search resulted in 1404 records, and only six studies (n = 252 participants) fulfilled the eligibility criteria and were included. The studies were published between 2013 and 2018. All studies showed a significant reduction in both salivary and serum urea/creatinine levels. All eligible studies presented a low risk of bias. The meta-analysis shows a moderate to high correlation between salivary and blood levels of urea (r: 0.79; 95% CI: 0.56-1.00) and creatinine (r: 0.64; 95%CI: 0.16-1.00), with a very low level of certainty. The reductions in salivary urea and creatinine levels are similar to and correlated with the reductions in blood urea and creatine levels after hemodialysis among chronic kidney disease patients.

Sialometric and Sialochemical Analysis in Individuals With Pulp Stones

The aim of this study was to analyze the saliva of patients with pulp stones, with sialometric and sialochemical tests. Eighty individuals, aged between18 and 65 years, of both sexes, were investigated. Patients were included in the pulp stone group when radiographic examination was suggestive of pulp stones in at least one permanent tooth, whereas those without this alteration were considered controls. Saliva was collected by stimulation, followed by salivary flowrate (SFR) and pH analysis tests. The organic components, such as urea (URE), glucose (GLU), total proteins (TPTs), alkaline phosphatase, creatinine (CRE), salivary amylase (SAM), and uric acid (URA), and the inorganic components, such as calcium, iron, and phosphorus, were evaluated by colorimetric techniques in an ultraviolet–visible (UV–vis) spectrophotometer. Differences among pulp stones and control groups were compared using Student’s t-test, with a significance level of p < 0.05. In both groups prevailed the female. Statistically significant differences between groups were observed for pH (p = 0.027), SFR (p = 0.002), alkaline phosphatase (p = 0.008), and URA (p = 0.005). None of the inorganic components showed significant difference (p > 0.05). In the analyses stratified by sex, difference between groups was observed for pH (p = 0.007) and URA (p = 0.003) in women. In conclusion, sialometric and sialochemical alterations occurred in patients with pulp stones, with significantly higher levels of pH, SFR, alkaline phosphatase, and URA.

Saliva as an alternative to blood in the determination of uremic state in adult patients with chronic kidney disease: a systematic review and meta-analysis

OBJECTIVES

To assess whether salivary urea and creatinine levels accurately reflect their serum levels in blood samples of adults to detect chronic kidney disease.

MATERIALS AND METHODS

A systematic review was conducted in eight electronic databases. The protocol was registered in PROSPERO. Only diagnostic test studies were included. The JBI critical appraisal tools assessed the risk of bias. A meta-analysis of proportions was performed. The GRADE tool assessed the quality of evidence and strength of recommendation across the studies included.

RESULTS

Eight studies met the eligibility criteria and were included. Six studies assessed salivary urea, and six studies assessed salivary creatinine. All studies presented moderate risk of bias. The meta-analysis depicted an overall sensitivity of 93.3% (95% CI = 88.6; 97.9) for salivary creatinine levels and 87.5% (95% CI = 83.2; 91.8) for salivary urea levels, while the overall specificity was 87.1% (95% CI = 82.8; 91.3) and 83.2% (95% CI = 65.0; 101.4) for salivary creatinine and urea levels, respectively. The overall accuracy of salivary creatinine was 5.2 percentage points higher compared with salivary urea levels (90.8% vs. 85.6%). According to the GRADE tool, the analysed outcomes were classified as having low to moderate level of certainty.

CONCLUSION

Compared with blood samples, salivary urea and creatinine levels presented high diagnostic values for chronic kidney disease screening, but should not be considered equivalent to levels obtained from blood at stages three, four, or five of the disease.

CLINICAL SIGNIFICANCE

Chronic kidney disease patients could receive a clinically significant benefit from replacing blood with saliva for potentially monitoring renal function. Saliva collection presents greater simplicity, comfort, safety, and lower collection cost.

Dual Roles of the Mineral Metabolism Disorders Biomarkers in Prevalent Hemodilysis Patients: In Renal Bone Disease and in Vascular Calcification

Background

Vascular calcification (VC) is highly prevalent in dialysis (HD) patients, and its mechanism is multifactorial. Most likely that systemic or local inhibitory factor is overwhelmed by promoters of VC in these patients. VC increased arterial stiffness, and left ventricular hypertrophy. Thus, the present study aimed to investigate the association of VC and myocardial remodeling and to analyze their relationship with VC promoters (fibroblast growth factor 23-FGF23, Klotho, intact parathormon-iPTH, vitamin D) in 56 prevalent HD patients (median values: age 54 yrs, HD vintage 82 months).

Methods

Besides routine laboratory analyzes, serum levels of FGF 23, soluble Klotho, iPTH, 1,25-dihydroxyvitamin D3; pulse wave velocity (PWV); left ventricular (LV) mass by ultrasound; and VCs score by Adragao method were measured.

Results

VC was found in 60% and LV concentric or eccentric hypertrophy in 50% patients. Dialysis vintage (OR 1.025, 95%CI 1.007–1.044, p=0.006) FGF23 (OR 1.006, 95% CI 0.992–1.012, p=0.029) and serum magnesium (OR 0.000, 95%CI 0.000–0.214, p=0.04) were associated with VC. Changes in myocardial geometry was associated with male sex (beta=-0.273, 95% CI -23.967 1.513, p=0.027), iPTH (beta 0.029, 95%CI -0.059–0.001, p=0.027) and vitamin D treatment (beta 25.49, 95%CI 11.325–39.667, p=0.001). Also, patients with the more widespread VC had the highest LV remodeling categories. PWV was associated patient’s age, cholesterol, diastolic blood pressure, LV mass (positively) and serum calcium (negatively), indicating potential link with atherosclerotic risk.

Conclusions

Despite to different risk factors for VC and myocardial remodeling, obtained results could indicate that risk factors intertwine in long-term treatment of HD patients and therefore careful and continuous correction of mineral metabolism disorders is undoubtedly of the utmost importance.