Why is it necessary that urine samples should be collected from the first urine voided in the morning?

Castle EP, Wolter CE, Woods ME. Evaluation of the urologic patient: testing and imaging. In: Partin AW, Dmochowski RR, Kavoussi LR, Peters CA, eds. Campbell-Walsh-Wein Urology. 12th ed. Philadelphia, PA: Elsevier; 2021:chap 2.

Germann CA, Holmes JA. Selected urologic disorders. In: Walls RM, Hockberger RS, Gausche-Hill M. Rosen's Emergency Medicine: Concepts and Clinical Practice. 9th ed. Philadelphia, PA: Elsevier; 2018:chap 89.

Nicolle LE, Drekonja D. Approach to the patient with urinary tract infection. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 268.

(See specific Microbiology Specimens sections for other instructions.)

Note: Please examine specimen collection and transportation supplies to be sure they do not include expired containers.

Urine Specimen Collection Products

Urinalysis and Culture and Susceptibility

Submit a urinalysis preservative tube and culture and susceptibility preservative tube. Label both filled tubes with the patient's first and last name and second identifier. Include the date and time of specimen collection on each specimen container.

Urinalysis Only

Submit a urinalysis preservative tube. Label filled tube with the patient's first and last name and second identifier. Include the date and time of specimen collection on each specimen container.

Culture and Susceptibility Only

Submit a culture and susceptibility preservative tube. Label the filled tube with the patient's first and last name and second identifier. Include the date and time of specimen collection on each specimen container.

Frozen Gel Packs. To ensure specimen integrity during warm weather, follow these Instructions for Use of frozen gel packs and specimen lockboxes.

Random Urine Collection for Routine Analysis

Patients should be provided with both written and spoken “clean-catch” instructions. When a clean-catch urine specimen is required, follow the directions given under Urine for Culture in the Microbiology Specimens: Bacteriology and Mycobacteriology Specimens section. The collected urine should be added to the appropriate urine preservative tube or refrigerated immediately to retard growth of bacteria until the test is performed.

Urine values vary considerably during a 24-hour period, and most test methods are based on normal values for first morning samples. The first urine voided in the morning is preferred because it has a more uniform volume and concentration and a lower pH, which helps preserve the formed elements. If it is not possible to obtain a first morning sample, the time of the sample should be noted on the test request form and in the patient's records.

Instructions for Use: Urine Monovette® With pH Stabilizer

Caution: The urine Monovette® contains a corrosive liquid that may cause severe burns to all areas of contact. Inhalation can cause irritation and burns, and it may be fatal if swallowed.

1. Friction fit the yellow suction tip securely onto the Luer end of the multi-adapter. (See Figure 1.)

2. Connect the multi-adapter to the urine Monovette® membrane cap via the three-pin locking mechanism. Guide the pins on the cap straight into the grooves of the adapter, then secure by twisting slightly clockwise. (See Figure 1.)

3. Place the suction tip down into the urine specimen and pull the urine Monovette® plunger to the black base fill line, drawing urine into the tube. The base fill line is located on the label near the bottom of the urine Monovette®. (See Figure 2.)

4. Hold the urine Monovette® upright, and fully extend the plunger to draw the remaining urine out of the yellow straw. (See Figure 3.)

5. Break off the plunger and place it in the proper receptacle.

6. Remove the straw from the Luer adapter and place it in the proper receptacle.

7. Disconnect the multi-adapter from the urine Monovette® membrane cap by twisting slightly counterclockwise, and dispose of the adapter in the proper sharps container. (See Figure 4.)

8. Label and submit the specimen according to LabCorp's procedures.

Routine 24-hour Urine Collection

For many urine chemistry tests, it is necessary to analyze a sample taken from an entire 24-hour excretion. Incorrect collection and preservation of 24-hour urine collections are two of the most frequent lapses in urine collections.

The 24-hour urine specimen should be submitted in a chemically clean, properly labeled urine container provided by LabCorp. (Patients should not be allowed to submit urine specimens in their own “clean” jars.) The laboratory adds required preservatives or supplies the proper preservative with the container.

Written instructions should clearly explain the following points.

1. The collection of the 24-hour urine starts with the patient voiding (completely emptying bladder) and discarding the first urine passed in the morning.

2. Except for this first discarded urine, all of the urine passed during that day and night, up to and including the first voiding of the following day, must be collected. Urine passed during bowel movements must also be collected.

3. If possible, the entire specimen should be refrigerated at 2°C to 8°C during collection, or kept in a cool place, since urine is an excellent culture medium for organisms, and its components decompose quickly.

4. The 24-hour urine container may contain a preservative of acetic acid, boric acid, or hydrochloric acid, which may cause burns if touched. If ingested, a physician should be contacted immediately.

The patient should be informed of the following recommended collection requirements.

1. A normal intake of fluids during the collection period is desirable unless otherwise indicated by the physician or test specimen requirements.

2. In some cases, it may be advisable for patients to discontinue taking all medications for an interval of at least 12 hours (preferably 48 to 72 hours) preceding the urine collection period. This is done as a precaution against interference in the chemical assays of various hormones; there may be instances, however, in which this is not recommended.

3. In certain complex chemical analyses, the metabolic products of certain foods and supplements (such as vitamins and minerals) may also cause misleading results. In these instances, the laboratory will advise the physician of special dietary restrictions to be communicated to the patient.

Finally, in preparing and submitting the specimen, you should always adhere to the following critical points.

1. If only a portion of the 24-hour collection is submitted to the laboratory, be sure to add the remaining portion, measure the entire 24-hour volume, and record the total amount in milliliters (mL) on the test request form for laboratory use. The specimen must be well mixed prior to pouring off aliquots of the sample into an appropriately labeled transport container and submitting it to the laboratory.

2. When aliquots are required with preservatives, use only the preservative requested. One preservative must not be substituted for another. Do not add preservatives except as specified by the laboratory.

3. Even in the healthy individual, the total daily urine volume may be highly variable depending upon water intake, diet, activity, and environmental factors. Be sure to provide the patient with a container of adequate size.

4. When the laboratory requires a pooled, well-mixed specimen (collected in more than one container) or a measured aliquot for an individual test, the specimen must be prepared exactly as stated in the specimen requirement. Submit this to the laboratory as soon as possible.

This section includes written instructions to be provided to the patient with the specified laboratory collection container. Supplement these instructions by discussing them with the patient and explaining why the test and collection procedures are necessary. Collection containers that include acids should be clearly marked.

To the Physician: You may wish to photocopy these pages so that you can provide your patients with written instructions.

To the Patient: Follow these instructions in collecting your 24-hour urine specimen.

Void (urinate) into the smaller container provided and transfer the urine into the larger collection container. Do not add anything but urine to the container and do not discard any liquid, tablets, or powder that may already be in the larger collection container. These substances may cause burns if touched. The collection container should be kept tightly closed and refrigerated (or kept in a cool place) throughout the collection period.

1. Upon rising in the morning, urinate into the toilet, emptying your bladder completely. Do not collect this sample. Note the exact time and print it on the container label.

2. Collect all urine voided for 24 hours after this time in the container provided by the physician. All urine passed during the 24-hour time period (day or night) must be saved. Urine passed during bowel movements must also be collected.

3. Refrigerate the collected urine between all voidings or keep it in a cool place.

4. At exactly the same time the following morning, void completely again (first time after awakening), and add this sample to the collection container. This completes your 24-hour collection.

5. Take the 24-hour specimen to the physician's office or laboratory as soon as possible, maintaining the cool temperature in transit by placing the specimen in a portable cooler or insulated bag.

Kidney Stone Retest

1. Provide the patient with two 24-hour specimen containers, one containing preservative (30 mL hydrochloric acid) and one containing no preservative.

2. This 24-hour urine container contains hydrochloric acid, which may cause burns if touched. If ingested, a physician should be contacted immediately.

3. Have the patient collect two consecutive 24-hour urine specimens according to the collection protocol provided in the accompanying patient directions. The first 24-hour specimen should be collected in the container with preservative. The specimens must be refrigerated during collection, and the two specimens should be returned to the office/laboratory as soon as possible after completion of the second collection.

4. Upon return of the two 24-hour urine specimens, they should be handled as follows.

a. Measure the total volume of each 24-hour specimen and record these volumes (in mL) on the test request form under “Clinical Information.” Be sure to identify which specimen was collected with preservative and which was collected without preservative. Example:

24-hour volume (preservative) = 2100 mL

24-hour volume (no preservative) = 1800 mL

b. After measuring the volumes, mix well and pour off an aliquot from each specimen into the special urine containers provided. These containers should be filled approximately three-fourths full (about 75 mL).

c. Label each aliquot with the patient's full name, the measured 24-hour urine volume, and whether the specimen was collected with or without preservative. Special kidney stone prevention profile labels are provided for your convenience.

5. Upon return of the 24-hour urine specimens, a fresh random urine specimen should be obtained from the patient for pH determination. Measure the pH urine using a dipstick, and record the value on the aliquot labels as well as on the test request form under “Clinical Information” (below the two urine volumes). This specimen should then be discarded.

6. Complete the test request form by providing all necessary information.

7. Complete the patient history (questionnaire [retest]), including all information required, and mail this to the laboratory. It is mandatory that this history be submitted; otherwise, a physician interpretation will not be performed. A prepaid envelope is supplied for your convenience.

8. Place the two urine aliquots in the plastic zip-lock specimen bag labeled “Kidney Stone Prevention.” The completed test request form goes in the side pocket of the bag. Store in the freezer.

Two Consecutive 24-hour Urine Collections: Patient Instructions

To the Physician: You may wish to photocopy these pages so that you can provide your patients with written instructions.

Follow the directions below to collect urine for analysis by your physician. Remember to store all urine in the refrigerator from the time collection begins until you take the containers to your physician. Important: Do not allow the urine from one container to mix with the urine in the other container. The urine container may contain a preservative of acetic acid, boric acid, or hydrochloric acid, which may cause burns if touched. If ingested, a physician should be contacted immediately.

First 24-hour Urine Collection (Hydrochloric Acid “HCl” Preservative)

1. Urinate in the usual manner on awakening, making sure to empty your bladder completely. Do not save this urine, but you must record the date and time of this first urination. Example: 03/13/01, 7:30 AM.

2. All urine passed during the remaining 24-hour period must be collected in this first container, labeled “HCl Preservative.” Urine passed during bowel movements must also be collected.

3. Urine may be collected in another clean container and then carefully poured into the first 24-hour collection container.

4. The next morning, urinate on awakening, but this time include the urine in the HCl preservative container. Record the date and time of this urination. Example: 03/14/01, 7:30 AM. This is the last sample to be included in the container marked “HCl Preservative.”

Second 24-hour Urine Collection (No Preservative)

1. Record the date and time of the first urine of the day. The time is the same as the last entry of the HCl preservative container. (See number 4 above.)

2. From now on, all urine passed for the next 24-hour period must be included in the second container, labeled “No Preservative.” Urine passed during bowel movements must also be collected.

3. Urine may be collected in another clean container and then carefully poured into the second container.

4. On the following morning, the first urine of the day must be included in this second container. Record the date and time of this urination. Example: 03/15/01, 7:30 AM. This is the last sample to be included in the container labeled “No Preservative.”

Urine Testing: Preservative Quick Reference Chart

Analyte

Sample

Time

Preser-

vative(s)

Target pH

Storage

Rejection

Criteria

Stability

Key: d = day(s); h = hour(s); m = month(s); w = week(s); y = year(s); FZ = frozen; RF = refrigerated; RT = room temperature

Albumin

Timed, random, or 24-hour

None

4-7

Refrigerate

Visual presence of blood in sample; pH <3

RT, RF, FZ: 14 d

Aldosterone

24-hour

None or boric acid

4-8

Refrigerate

Original container with pH <2

With boric acid:

RT: 7 d, RF, FZ: 14 d

Amino acids, quantitative

Random or 24-hour

None

 

Freeze

 

RT, RF: unstable, FZ: 14 d

Aminolevulinic acid (ALA)

Random or 24-hour

Acetic acid; protect from light

<6

Freeze

Unprotected from light

Preserved (acidified) and protected from light:

RF: 3 d, FZ: 1 m

Amylase

24-hour

None

 

Refrigerate

 

RT, RF: 14 d

Arsenic

Random or 24-hour

None

 

Room temperature

 

RT, RF, FZ: 14 d

β2-microglobulin

Random

None

6-8

Refrigerate

 

pH 6-8:

RT, RF: 7 d, FZ: 14 d

Benzene metabolite

Random (sampling time is end of shift of industrial exposure monitoring)

None

 

Room temperature

 

RT: 7 d, RF, FZ: 14 d

C-Peptide, urine

Random or 24-hour

None or boric acid

4-7

Freeze

pH <3; pH >8

RT: 1 d, RF: 7 d, FZ: 348 d

Cadmium

Random or 24-hour

None

 

Room temperature

 

RT, RF, FZ: 14 d

Calcium

24-hour

6N HCl

<2

Room temperature

 

Acidified (pH <2):

RT, RF: 14 d

Cannabinoids:creatinine ratio

Random

None

 

Refrigerate

 

No preservative;

RT: 7 d, RF, FZ: 14 d

Catecholamines, fractionated, total

Random or 24-hour

6N HCl

0-3

Refrigerate

Original container with pH >5; specimen without preservative. Note: If original container is received with pH >3 but <5, adjust pH to <3 with 6N HCl.

Acidified (pH <5):

RT: 3 d, RF: 14 d, FZ: 30 d

Chloride

24-hour

None

 

Room temperature or refrigerate

Collection with HCl

Refrigerated during collection:

RT, RF, FZ: 14 d

Chromium

Random

None

 

Room temperature

 

RT, RF, FZ: 14 d

Citric acid

24-hour

6N HCl or frozen with no preservative

1-3

Freeze

Acetic or boric acid

Acidified:

RT, RF: 14 d

Nonacidified:

FZ: 14 d

Cobalt

Random or 24-hour

None

 

Room temperature

 

RT, RF, FZ: 14 d

Copper

Random or 24-hour

None

 

Room temperature

 

RT, RF, FZ: 14 d

Cortisol, free

24-hour

None or any

 

Refrigerate

 

RT, RF, FZ: 14 d

Creatine

24-hour

None

 

Freeze

6N HCl, boric acid, or alkali added; thawed specimen

 

Creatinine

Random or 24-hour

None or any

 

Room temperature, refrigerate, or freeze

 

RT: 7 d, RF, FZ: 14 d

Cyclic AMP

Random

None

 

Freeze

 

FZ: 14 d

Cystine

24-hour

None, 6N HCl or 1g/L Boric Acid

Freeze

Receipt of non-frozen sample

FZ: 14 d

Glucose

24-hour

Boric acid or NaF

 

Refrigerate

 

RF: 14 d

Heavy metals

Random or 24-hour

None

 

Room temperature

 

RT, RF, FZ: 14 d

Histamine

24-hour

None

 

Room temperature

 

RT: 14 d

Homovanillic acid (HVA)

Random or 24-hour

None or 6N HCl

 

Room temperature

 

RT, RF, FZ: 14 d

Hydroxyindoleacetic acid (HIAA)

Random or 24-hour

None or boric acid

4-8

Refrigerate

Original container with pH <2

RT: 7 d, RF, FZ: 14 d

Immunofixation

Random or 24-hour

None

 

Room temperature

 

RT, RF, FZ: 14 d

Lead

Random or 24-hour

None

 

Room temperature

 

RT, RF, FZ: 14 d

Magnesium

24-hour

6N HCl

<2

Refrigerate

No preservative; presence of blood; improper labeling

Collect with no preservative: acidify to pH 1 prior to assay.

RT, RF, FZ: 14 d

Mercury

Random or 24-hour

None

 

Room temperature

 

RT, RF, FZ: 14 d

Metanephrines (total and fractionated)

Random or 24-hour

None or 6N HCl

 

Refrigerate

 

Nonacidified:

RT: 3 d, RF: 14 d

Acidified:

RT, RF, FZ: 14 d

Myoglobin

Random

None

 

Refrigerate

 

Unstable in acid pH; RF: 3 d, FZ: 14 d

Nickel

Random or 24-hour

None

 

Room temperature

 

RT, RF, FZ: 14 d

Osmolality

Random or 24-hour

None

 

Refrigerate

 

RT, RF, FZ: 14 d

Oxalate

24-hour

6N HCl

0-2

Room temperature or refrigerate

Improper labeling

Acidified:

RT, RF: 7 d

FZ: 14 d

Phenol

Random

None

 

Room temperature

 

RT: 7 d, RF, FZ: 14 d

Phosphorus

24-hour

6N HCl

0-2

Room temperature

 

Acidified:

RT, RF, FZ: 14 d

Porphobilinogen (PBG)

Random or 24-hour

Acetic acid; protect from light

 

Freeze

Container received unfrozen; container not protected from light

RF: 24 h

Preserved with acetic acid: FZ: 1 m

Porphyrins

Random or 24-hour

Sodium carbonate or none; protect from light

 

Refrigerate

Container not protected from light

RT: unstable, RF: 7 d, FZ: 14 d

Potassium

24-hour

None or 6N HCl

 

Room temperature

 

RT, RF: 14 d

Pregnancy test

Random (use first morning specimen)

None

 

Refrigerate

   

Protein, total

24-hour

None

 

Refrigerate

Visual presence of blood in sample; pH <3

RT, RF, FZ: 14 d

Selenium

Random or 24-hour

None

 

Room temperature

 

RT: 7 d, RF, FZ: 14 d

Sodium

24-hour

None or 6N HCl

 

Refrigerate

 

RT, RF: 14 d

Urea nitrogen

24-hour

None

 

Refrigerate

 

RT, RF, FZ: 14 d

Uric acid

24-hour

None

 

Room temperature or refrigerate

Original container with acid, pH <6

RT, RF: 14 d

Vanillylmandelic acid (VMA)

Random or 24-hour

None or 6N HCl

 

Room temperature

 

RT: 7 d, RF, FZ: 14 d

Xylose tolerance

5-hour

None

 

Room temperature

   

Zinc

Random or 24-hour

None

 

Room temperature

 

RT, RF, FZ: 14 d