2.3 Urine preservations [AUBF - Specimen preservation, pp. 31-32 - Prelim

The method of preservation used most routinely is refrigeration at 2°C to 8°C, which decreases bacterial growth and metabolism.

Refrigeration

• Does not interfere with chemical tests.

• Precipitates amorphous phosphates and urates.

  • Prevents bacterial growth for 24 hours.

Acids (boric acid, HCL, acetic acid, tartaric acid)

• Prevents bacterial growth and metabolism.

• Interferes with analysis of drugs and hormones.

• Keeps pH at about 6.0 Can be used for transport of urine cultures

Formalin (formaldehyde)

• Excellent sediment preservative.

• Acts as a reducing agent, interfering with chemical tests for glucose, blood, leukocyte esterase, and copper reduction.

• Rinse specimen container with formalin to preserve cells and casts.

Sodium fluoride

• Good preservative for drug analyses.

• Inhibits reagent strip tests for glucose, blood, and leukocytes.

Commercial preservative tablets

• Convenient when refrigeration not possible Have controlled concentration to minimize interference.

• Check tablet composition to determine possible effects on desired tests

Urine collection kits (Beckton, Dickinson, Rutherford, NJ)

Contains collection cup, transfer straw, culture and sensitivity (C&S) preservative tube, or UA tube.

Light gray and gray C&S tube

• Specimen stable at room temperature (RT) for 48 hours; prevents bacterial growth and metabolism.

• Do not use if urine is below minimum fill line.

• Preservative is boric acid, sodium borate, and sodium formate Keeps pH at about 6.0.

Yellow UA plus tube

• Use on automated instruments.

• Must refrigerate within 2 hours.

• Round or conical bottom, no preservative.

Cherry red/yellow preservative plus tube

• Specimen stable for 72 hours at RT; instrument-compatible.

• Must be filled to minimum fill line.

• Bilirubin and urobilinogen may be decreased if specimen is exposed to light and left at RT.

• Preservative is sodium propionate, ethyl paraben, and chlorhexidine.

• Round or conical bottoms.