PAROTID-FLUID UREA NITROGEN FOR THE MONITORING OF HEMODIALYSIS

Diagnostic Performance of a Saliva Urea Nitrogen Dipstick to Detect Kidney Disease in Malawi

INTRODUCTION

Kidney disease (KD), including acute kidney injury, is common, severe and leads to significant mortality in the developing world. However, simple tools to facilitate diagnosis and guide treatment are lacking. We studied the diagnostic performance of saliva urea nitrogen (SUN) measured by dipstick to diagnose KD in a low-resource setting.

METHODS

Medical admissions to a tertiary hospital in Malawi had serum creatinine tested at presentation; SUN was measured using a dipstick. Patients with serum creatinine above normal range underwent serial measurements of SUN and blood urea nitrogen for up to 7 days. Hospital outcome was recorded in all patients.

RESULTS

A total of 742 patients were included (age 41 ± 17·3 years, 56.1% male); 146 (19.7%) had KD, including 114 (15.4%) with acute kidney injury. SUN >14 mg/dl had a sensitivity of 0.72 and a specificity of 0.87 to diagnose KD; specificity increased to 0.97 when SUN levels were combined with self-reported urine output. The diagnostic performance of SUN was comparable with the one of blood urea nitrogen (SUN area under curve, 0.82; 95% confidence interval, 0.78-0.87; blood urea nitrogen area under curve, 0.82; 95% confidence interval, 0.59-1.0). SUN >14 mg/dl on admission was an independent predictor of all-cause mortality (hazard ratio = 2.43 [95% confidence interval, 1.63-3.62]).

DISCUSSION

SUN measured by dipstick can be used to identify patients with KD in a low-resource setting. SUN is an independent predictor of mortality in this population.

International Society of Nephrology's 0by25 initiative (zero preventable deaths from acute kidney injury by 2025): focus on diagnosis of acute kidney injury in low-income countries

In developing countries with limited medical infrastructure, preservation and recovery of renal function following acute kidney injury (AKI) is difficult. In conjunction with clinical presentation, rapid measurement of renal function is essential for early diagnosis and management. Especially in low- and middle-income countries, simple interventions such as hydration and avoidance of toxins have the highest probability of recovery. In such contexts, measurement of urine volume and osmolality and serum creatinine with point-of-care devices and saliva urea nitrogen dipsticks can be valuable. This review aims to identify currently available methodologies to assist in reaching the ambitious goal of the 0by25 initiative to eliminate all preventable deaths from AKI by 2025.

Assessment of salivary urea as a less invasive alternative to serum determinations

OBJECTIVE

Experimental studies describe how urea is excreted through salivary glands and correlates with serum levels independently of salivary flow rate. This study confirms that salivary urea (SaU) is a reliable biomarker of uraemic state. In order to validate the SaU methodology, the following factors were taken into account: the independence of urea levels from saliva flow rate in healthy subjects and patients with chronic renal failure and the agreement between SaU and serum urea (U) levels in the entire population. In addition, reference intervals and cut-off values for SaU and U were established.

MATERIAL AND METHODS

Urea levels were determined in 268 matched whole saliva (SaU) and serum (U) samples obtained simultaneously from 78 healthy individuals and 154 patients with chronic renal failure. A serum enzymic colorimetric assay was adapted to SaU determinations.

RESULTS

SaU was independent of salivary flow rate. The agreement between SaU and U was confirmed by Bland-Altman analysis with a significant correlation between them (r = 0.91, p = 0.0001). The reference interval of SaU ranged from 1.66 to 7.5 mM. The cut-off values for SaU and U were 7.5 mM and 8.2 mM, respectively (sensitivity and specificity 100% for both).

CONCLUSIONS

SaU testing is harmless and useful for ruling out azotemic states in outpatients. Our results support the inclusion of SaU as a diagnostic test in the clinical laboratory.

Sampling Airway Surface Liquid: Non-Volatilesin the Exhaled Breath Condensate

Exhaled breath condensate (EBC) samples contain molecules that have no appreciable vapor pressure; such molecules likely derive from droplets of airway fluid. We analyzed EBC gathered from a total of 62 healthy volunteers in order to quantify the volume of airway liquid that was the source of the non-volatiles; saliva was analyzed as a reference secretion. EBC urea averaged 0.52 +/- 0.12 micromol/L (n = 18), an 8,600-fold dilution from predicted blood urea nitrogen levels. Protein averaged 2.3 +/- 0.3 microg/ml (n = 31), three orders of magnitude less than in saliva (1.4 +/- 0.1 mg/ml, n = 15). EBC ammonia was 6.6 +/- 0.6 mmol/L (1/15 that of saliva) and EBC ammonium ion was 0.90 +/- 0.19 micromol/L, concentrations that are incompatible with an 8,600-fold dilution from a biological source. Thus, urea-derived dilution factors may be used to interpret EBC non-volatile molecules, but not EBC volatiles.