ESPN 51th Annual Meeting

ESPN 2018


 
Urinary ammonium measured by automated methods in healthy children
LEYRE CARDO 1 HELENA GIL-PEñA 1 MARIA LUISA ALVAREZ-IZQUIERDO 1 JULIAN RODRIGUEZ-SUAREZ 1 FRANCISCO V ALVAREZ 1 FERNANDO SANTOS 1

1- HOSPITAL UNIVERSITARIO CENTRAL DE ASTURIAS & UNIVERSITY OF OVIEDO
 
Introduction:

 

Background: Measurement of urine ammonium (UA) plays a central role in the differential diagnosis of patients with metabolic acidosis, such as renal tubular acidosis, and recent data indicate that UA may be a marker of kidney fibrosis in patients with chronic kidney disease.  In most laboratories UA is assessed indirectly because its measurement is cumbersome.

Objectives: To establish reference values of urine ammonium/creatinine ratio (UA/UCr) in pediatric population by an automated method.

Material and methods:

 

UA and Ucr concentrations were measured in single urine samples of 164 children between 2 and 17 year old (X±SD 9.2±2.7 years) without concurrent renal, metabolic or systemic disease. After confirming in a limited number of samples that the following procedures did not modify measured UA values with respect to measurement in fresh urines, samples were collected in urine Vacuette tubes with no additive, centrifuged  (1500 rpm, 10 minutes) and supernatant was separated and kept frozen (-20ºC) until analysis in a Cobas c501 analyzer (Roche Diagnostics) by adaptation of automated plasma ammonium assays (urine samples were diluted 1:100 in sterile water and assayed as plasma samples). Results are expressed as µmol of ammonium/g of creatinine. Reference values were calculated following the Clinical & Laboratory Standards Institute guideline C28-A3, by the robust method, using the software MedCalc (v 12.5.0.0).

Results:

 

UA/UCr did not follow a normal distribution (Kolmogorov-Smirnov test). UA/UCr median value was 36 µmol/g, ranging from 11 (90% Confidence Interval 9.7 to 13.4) to 108 (90% Confidence Interval 94.2 to 123.5) µmol/g. 

Conclusions:

 

This study provides values of ammonium in single urine samples, measured by an enzymatic method which can be reliably and feasibly carried out in clinical laboratories. Elimination of ammonium is influenced by acid-base status and intake of nonvolatile acids but the UA/UCr ratios here given may be useful as reference values in normal children.