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What is the gray top urinalysis tube used for?


The gray top urinalysis tube, also known as a gray top tube or gray top vacutainer tube, is an important tool used to collect and transport urine samples for urinalysis testing. Urinalysis provides information about a patient’s health by analyzing the physical and chemical properties of their urine. The gray top tube allows urine samples to be collected and preserved properly until they can be analyzed.

What is Urinalysis?

Urinalysis is a diagnostic laboratory test that evaluates a patient’s urine sample. It is one of the most common methods of medical testing performed today. Urinalysis provides key information to assist doctors in the diagnosis of many conditions and diseases including:

  • Urinary tract infections
  • Kidney disease
  • Diabetes
  • Liver problems
  • Metabolic disorders
  • Pregnancy complications

The urinalysis provides both physical and chemical analysis of the urine. Physical properties examined include urine color, clarity, odor, and concentration. Chemical analysis looks at levels of various substances dissolved in the urine such as glucose, proteins, ketones, blood, bilirubin, nitrites, leukocyte esterase, and more.

By analyzing these various urinary factors, urinalysis can provide insight into hydration status, kidney and liver function, infections, diabetes management, pregnancy status, and other health indicators. It allows detection of diseases and abnormalities that may not manifest obvious symptoms at an early stage.

Why Use a Special Tube for Urine Collection?

Urine can be easily contaminated and properties changed if not collected and stored properly. Using the right urine collection tube preserves the sample in its original state until urinalysis can be performed.

Some key reasons why a specialized tube is important include:

  • Maintain sterility – The tube keeps the sample sterile and free from external contaminants that could alter test results.
  • Stabilize composition – Chemicals in the tube stabilize the urine composition and prevent changes to the properties being tested.
  • Prevent leakage – The tube is tightly sealed to prevent spillage and leakage during transport.
  • Measure volume – Graduations on the tube allow the collection of specific urine volumes needed for different tests.
  • Easy labeling – Tubes are designed for easy labeling with patient name, date, etc. for identification.

Gray Top Tube Uses

The gray top vacuum tube is the recommended urine collection tube for most routine urinalysis testing. Some key uses of the gray top urinalysis tube include:

General Urinalysis

The gray top tube is ideal for collection of a random urine sample when a general urinalysis is ordered. This may screen for overall health, kidney function, hydration, infections, etc. with a standard dipstick test strip. A midstream clean catch urine sample of 10-50mL is appropriate.

Microscopic Urinalysis

For microscopic urinalysis where urine sediment is examined under a microscope, a first morning urine sample of 5-10mL is preferred. The gray top tube will stabilize cellular structures like red blood cells and white blood cells until microscopy can be performed.

Culture Testing

Urine cultures are used to identify and characterize infections. Larger urine volumes of up to 100mL may be collected in the gray top tube for culturing. The tube preservatives ensure any bacteria present can be grown in the lab.

Pregnancy Testing

Gray top tubes can collect the first morning urine samples recommended for sensitive pregnancy tests. Human chorionic gonadotropin (hCG) levels are most concentrated early in the day. The tube maintains the sample integrity for accurate hCG level measurement.


Rarer cytology urinalysis examining urine cell morphology may require collection of an entire first morning urine void. The larger gray top tubes allow adequate volume for this testing.

How Does the Gray Top Tube Work?

Gray top vacuum tubes utilize a special additive to stabilize and preserve urine specimens. The tube contains a powdered form of Lyophilized Boric Acid.

When urine is drawn into the tube, the following actions occur:

  • The urine dissolves the boric acid powder into solution.
  • The boric acid solution acts as an antimicrobial preservative, preventing growth of bacteria and degradation of the sample.
  • It creates an acidic environment ideal for preserving the urine pH, cells, casts, crystals, and chemical composition until analysis.
  • The solution adjusts the specific gravity of the urine to a consistent baseline value for accurate analysis.

Together, these effects inhibit changes to the properties of the urine. This allows test results to accurately reflect the patient’s physiology when the sample was collected.

Tube Appearance and Labeling

The gray top tube has the following distinguishing features:

  • Gray plastic cap
  • Clear glass barrel allows visual inspection of sample
  • Graduated volume markings from 1mL to 100mL
  • Large label area for patient identification

Labels should clearly state:

  • Patient full name
  • Date and time of collection
  • Any other specimen information

Proper labeling helps ensure the sample is processed correctly and results are reported accurately.

How to Collect a Sample with the Gray Top Tube

The following steps should be followed when collecting urine in a gray top vacuum tube:

  1. Verify tube is not expired and boric acid powder is present.
  2. Select an appropriate urine collection method (midstream clean catch,etc).
  3. Remove cap from tube, being careful not to touch the interior.
  4. Collect urine sample directly into tube. Fill to desired volume based on test(s) needed.
  5. Recap tube immediately after collection.
  6. Label tube clearly with patient name, date, time, etc.
  7. Follow any additional instructions from the requesting physician.
  8. Transport sample to the lab promptly after collection.

Proper technique is vital to get an accurate urinalysis result. Following the steps above helps maintain integrity of the sample.

Gray Top Tube Storage

Once collected, urine in a gray top tube is stable at room temperature for up to 24 hours. Refrigeration can extend stability up to 48 hours when needed. Freezing urine samples is not recommended as cells will lyse when thawed.

Long term storage is not advised in the gray top urinalysis tube. Ifarchiving is desired, the lab should transfer urine from the tube into a sterile polypropylene vial. This separate storage container will maintain integrity for several years when frozen at -20 degrees Celsius or colder.

Always refer to manufacturer guidelines and lab procedures for any specific handling instructions. Proper storage and transport are vital to obtaining accurate test results from urinalysis.

Advantages of the Gray Top Tube

Key benefits provided by the gray top urine collection tube include:

  • Maintains sample integrity for reliable test results
  • Used for a wide variety of urinalysis tests
  • Easy to label with clear marking area
  • Vacuum draw fills tube reliably each time
  • Clear glass allows visual inspection
  • Graduated volumes simplify collection of correct amounts
  • Stable at room temperature up to 24 hours
  • Standardized tool for consistent urinalysis

For these reasons, the gray top tube is widely used in healthcare settings when urinalysis is ordered. It provides an efficient means to collect, transport, and store urine until testing can be performed.

Limitations of Gray Top Tubes

While very useful, gray top urinalysis tubes do have some limitations including:

  • Not suitable for all urine tests – Some specialized assays require different preservatives
  • Requires specific handling – Samples need prompt delivery to lab to avoid deterioration
  • Single use only – Tubes cannot be reused or refilled after initial draw
  • Volume limitations – Large volumes exceeding tube capacity require alternate collection methods
  • Additive reduces concentration – Dilution effect must be considered when interpreting results
  • No long term storage – Separate freezer vials needed for archiving samples

Understanding these limitations helps ensure the appropriate collection method is used for each urine test ordered. In some cases, an alternate tube or collection container may be recommended.


The gray top tube is the standard vacuum collection container used for most routine urinalysis testing. Its unique additive preserves urine in its original state to allow accurate analysis of physical properties, chemical content, cell morphology and culture growth.

Following the proper collection protocol is key to obtaining a representative urine specimen in the gray top tube. Timely delivery to the lab will maintain integrity until automated chemistry, microscopic examination, pregnancy testing, and culturing can be performed. While some limitations exist, the gray top tube meets the collection needs for the majority of urinalysis orders. Its consistent use across healthcare ensures standardization of important baseline urine testing.