The preservation of urine samples for determination of renal stone risk factors.

Author(s): Nicar MJ, Hsu MC, Johnson T, Pak CY

Publication: Lab Med, 1987, Vol. 18, Page 382-4

PubMed ID: 11539109 PubMed Review Paper? No

Purpose of Paper

The purpose of this paper was to assess the effect of a 5 d processing delay at 4 degrees C, and the effectiveness of three preservatives used to prevent bacterial contamination on 13 clinical analytes in case-matched urine specimens collected over a 24 h period.

Conclusion of Paper

Storage of specimens for an additional 5 days at 4 degrees C prior to analysis only caused a slight increase in specimen pH, but elevated temperature, increased bacterial load, and increased storage duration resulted in a significant decrease in calcium, citrate, and creatinine and an increase in oxalate, ammonia and pH. The addition of thymol to the high bacterial load specimens prevented the decrease in citrate and blunted the change in ammonia. The use of thymol with HCl and boric acid in these specimens caused an expected decline in pH and precipitation of the uric acid but returned all other values to normal. The authors conclude that refrigeration of a specimen for 5 d or preservation with thymol in combination with HCl and boric acid allows for accurate quantification of most kidney stone markers in urine specimens.

Studies

Study Purpose

The purpose of this study was to assess the effects of a 5 d pre-processing delay at 4 degrees C compared to case-matched control specimens that were refrigerated at 4 degree C no longer than 24 h prior to processing. Specimen pH was determined prior to processing. Urine processing entailed the following analyte-specific preservation methods: addition of hydrochloric acid to a urine pH of 1.0 followed by refrigeration (calcium, magnesium, phosphorus, oxalate, ammonia, citrate, sulfate), refrigeration (sodium, creatinine), or addition of chloroform followed by refrigeration (uric acid) until analysis. Analysis was conducted within 1-2 weeks of processing.

Summary of Findings:

Storage of the specimen for an additional 5 days at 4 degrees C prior to processing only caused a slight increase in specimen pH (6.52 to 6.61, p<0.05). Slight declines in citrate (5.6%) and oxalate (10.5%) were also noted but not significant. No precipitation or bacterial odor was detected in stored specimens.

Biospecimens

Bodily Fluid - Urine

Preservative Types

Other Preservative

Diagnoses:

Other diagnoses

Platform:

Analyte	Technology Platform
Small molecule	pH
Small molecule	Clinical chemistry/auto analyzer
Electrolyte/Metal	Clinical chemistry/auto analyzer
Small molecule	Colorimetric assay
Small molecule	Radioimmunoassay

Pre-analytical Factors:

Classification	Pre-analytical Factor	Value(s)
Storage	Storage temperature	4 degrees C
Storage	Storage duration	Less than 1 d 5 d

Study Purpose

The purpose of this study was to assess the combined effect of urine specimen bacterial contamination (inoculation with 1 of 3 strains) and a heating regime (37 degrees C for 1 d, 65 degrees C for 1 d, then room temperature for 1 d) prior to specimen processing on 13 clinical analytes. The effectiveness of 3 chemical preservatives added prior to bacterial inoculation and specimen heating was also evaluated. Controls were untreated case-matched specimens that were stored at 4 degrees C no longer than 24 h prior to processing. Specimen pH was determined prior to processing. Urine processing entailed the following analyte-specific preservation methods: addition of hydrochloric acid to a urine pH of 1.0 followed by refrigeration (calcium, magnesium, phosphorus, oxalate, ammonia, citrate, sulfate), refrigeration (sodium, creatinine), or addition of chloroform followed by refrigeration (uric acid) until analysis. Analysis was conducted within 1-2 weeks of processing.

Summary of Findings:

The elevated temperature, increased bacterial load, and increased storage duration resulted in significant decreases in calcium (14%), citrate (37.7%), and creatinine (10.8%) and increases in oxalate (31.4%) ammonia (84%) and pH (3.6%). The addition of thymol to specimens prevented the decrease in citrate and blunted the change in ammonia (21%). The use of thymol with HCl and boric acid caused an expected decline in pH and precipitation of the uric acid. Citrate and cAMP were not measured in acidic specimens due to methodological limitations. The authors conclude that the use of thymol alone is insufficient but in combination with hydrochloric and boric acid it is an acceptable preservation technique.

Biospecimens

Bodily Fluid - Urine

Preservative Types

Other Preservative
None (Fresh)

Diagnoses:

Other diagnoses

Platform:

Analyte	Technology Platform
Small molecule	Radioimmunoassay
Small molecule	pH
Small molecule	Clinical chemistry/auto analyzer
Small molecule	Colorimetric assay
Electrolyte/Metal	Clinical chemistry/auto analyzer

Pre-analytical Factors:

Classification	Pre-analytical Factor	Value(s)
Storage	Storage temperature	37 degrees C 65 degrees C Room temperature 4 degrees C
Biospecimen Preservation	Type of fixation/preservation	None (fresh) Refrigeration Thymol
Biospecimen Preservation	Fixative additive/buffer	Hydrochloric acid None Boric acid

You Recently Viewed

News and Announcements

Most Downloaded SOPs in 2024

New Articles on the GTEx Project are Now FREELY Available!

Just Published!

More...