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Implications for the use of acid preservatives in 24-hour urine for measurements of high demand biochemical analytes in clinical laboratories.

Author(s): Feres MC, Bini R, De Martino MC, Biagini SP, de Sousa AL, Campana PG, Tufik S

Publication: Clin Chim Acta, 2011, Vol. 412, Page 2322-5

PubMed ID: 21910978 PubMed Review Paper? No

Purpose of Paper

Conclusion of Paper

Studies

1. Study Purpose

   This study investigated the effects of preserving urine with HCl in the collection container or addition of HCl after collection on the measured levels of 12 analytes that normally do not require HCl preservation. Twenty-four-hour urine specimens were collected from 22 volunteers into containers with 0, 5, or 20 ml/L 6 M HCl on non-consecutive days. After delivery to the laboratory, the specimens without preservatives were separated into aliquots before addition of 5 ml/L HCl. All specimens were stored at -20˚C until analysis. Levels of uric acid, creatinine, urea, chlorides, glucose, magnesium, sodium, potassium, microalbumin, proteins, amylase, and aldosterone were determined by an ADVIA 2400-clinical chemistry analyzer.

   Summary of Findings:

   Unacceptable coefficients of variance were observed for uric acid, glucose, microalbumin, and amylase when specimens were preserved with HCl, regardless of timing or amount, when compared to non-preserved specimens. Further, specimens preserved with 20 ml/L HCl in the collection container or with 5 ml/L HCl added after delivery resulted in unacceptable CV in the measurement of proteins compared to non-preserved specimens. Although the correlations between non-preserved and HCl-preserved specimens was very strong for most analytes (r=0.93-0.99);  uric acid displayed weak (r=0.37 for 20 ml/L HCl) to moderate (r=0.58 for 5 ml/L HCl in container or added after) correlations, amylase displayed very weak (r=0.03 and r= 0.00 when 5 or 20 ml/L HCl was in the collection container) to weak (r=0.32 when 5 ml/L HCl was added in the laboratory) correlations, and aldosterone displayed very weak (r=0.17 and r= 0.12 when 5 or 20 ml/L HCl was in the collection container) to modest (r=0.66 when 5 ml/L HCl was added in the laboratory) correlations. No significant differences in the CV were noted after acidification for creatinine, urea, chloride, magnesium, potassium, or sodium.

    

   Biospecimens

   • Bodily Fluid - Urine

   Preservative Types

   • Frozen

   Diagnoses:

   • Not specified

   Platform:

   Analyte	Technology Platform
   Carbohydrate	Clinical chemistry/auto analyzer
   Small molecule	Clinical chemistry/auto analyzer
   Protein	Clinical chemistry/auto analyzer
   Electrolyte/Metal	Clinical chemistry/auto analyzer

   Pre-analytical Factors:

   Classification	Pre-analytical Factor	Value(s)
   Biospecimen Preservation	Concentration of fixative	5 ml/L of 6 M HCl 20 ml/L of 6 M HCl 0 ml/L of 6 M HCl
   Biospecimen Preservation	Type of fixation/preservation	Hydrochloric acid Frozen

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2. Study Purpose

   The purpose of this study investigate the effects of not adding HCl or lower concentrations of HCl on the  levels of 6 analytes usually preserved by the addition of 20 ml/L HCl. Twenty-four hour urine specimens were collected from 22 volunteers into containers with 0, 5 or 20 ml/L 6 M HCl on non-consecutive days. After delivery to the laboratory, the specimen without preservatives was separated into aliquots before addition of 5 ml/L HCl. All specimens were stored at -20˚C until analysis. Levels of calcium, cortisol, phosphorus, citric acid, oxalate, and metanephrines were determined by a ADVIA 2400-clinical chemistry analyzer.

   Summary of Findings:

   Unacceptable CV from specimens preserved with 20 ml/L HCl was noted for cortisol and oxalate when specimens were not preserved or were preserved with 5 ml/L HCl in the container or after collection and for metanephrines when 5 ml/L HCl was in the collection container, but not when no preservative was present. Further, the correlation between results from specimens preserved with 20 ml/L HCl and those preserved with 5 ml/L HCl in the container was modest for cortisol (r=0.62) and oxalate (r=0.67). The correlation between specimens preserved with 20 ml/L HCl and those preserved with 5 ml/L HCl after arrival in the laboratory was modest for cortisol and strong for citric acid (r=0.77) and oxalate (r=0.70). Similarly the correlation between results from specimens preserved with 20 ml/L HCl and those not preserved with HCl was weak for cortisol (r=0.31) and modest for oxalate (r=0.42).

    

   Biospecimens

   • Bodily Fluid - Urine

   Preservative Types

   • Frozen

   Diagnoses:

   • Not specified

   Platform:

   Analyte	Technology Platform
   Electrolyte/Metal	Clinical chemistry/auto analyzer
   Steroid	Clinical chemistry/auto analyzer
   Small molecule	Clinical chemistry/auto analyzer
   Protein	Clinical chemistry/auto analyzer

   Pre-analytical Factors:

   Classification	Pre-analytical Factor	Value(s)
   Biospecimen Preservation	Concentration of fixative	5 ml/L of 6 M HCl 0 ml/L of 6 M HCl 20 ml/L of 6 M HCl
   Biospecimen Preservation	Type of fixation/preservation	Frozen Hydrochloric acid

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