The Best Principles and Practices for Specimen Collection you Must know

1. Have an understanding of the microbiology laboratory’s source identification schemes. Know when to include “rule-out” request. For example, the laboratory may routinely screen for Shigella, Salmonella, and Campylobacter species in stool cultures but not for Yersinia or Vibrio species.
2. Put in consideration geographic location and season when notifying the laboratory of rule out requests. For example, Coccidioides immitis is endemic in the southwestern United States, and rotaviruses are more commonly found in infants and children in winter.
   Identify the specimen source and/or specific site correctly so that proper culture media will be selected during processing the laboratory.
3. Obtain specimens before administering antimicrobial agents whenever possible.
4. Obtain specimen with as little contamination from indigenous microbiota as possible to ensure that the sample will be representative of the infected site.
5. Make use of appropriate collection devices. Use sterile equipment and aseptic technique to collect specimens to prevent introduction of microorganisms during invasive procedures.
6. label clearly the specimen container with the patient’s name and identification number or date of birth (DOB). Always include date and time of collection and your initials.
7. Collect an enough amount of specimen. insufficient amounts of specimen may give false-negative results.

(a). Requisition

The laboratory requisition (“lab slip”) must have the following information:

• Patient name
• Patient age and sex
• Date and hour of specimen collection
• Clinical diagnosis, special culture request, relevant patient history
• Special procedures used in obtaining specimen
• Name o f individual transcribing orders
• Antimicrobials, if any, patient is receiving
• Patient room number or address
• Physician name and address (or place physician can be located)
• Specific anatomic culture site

The requisition form must provide as much information as needed for correct interpretation of laboratory results. The need for the patient’s name and location is obvious. The patient’s age may be important in certain instances; e.g., if special culture techniques are needed or special pathogens considered. The physician’s name and location is essential so that interim reports can be given. The exact anatomical culture site, clinical diagnosis, and special collection procedures utilized are essential for the microbiologist in selecting appropriate culture media. The name o f person transcribing orders is needed should problems concerning the culture request arise.

(c). Collection times

1. The right times for specimen collection should be based upon both the type of infectious disease process and the ability of the laboratory to expertly process samples. Laboratories are normally better staffed during daytime hours to receive specimens. The microbiology laboratory may not be well staffed during evening and late night hours. Samples collected late in the evening often do not produce adequate growth by the next morning. However, provisions must be made to handle urgent samples during “off” hours, and consultation with supervisory personnel is highly recommended.

2. Twenty-four-hour specimen collections for culture must be discouraged and accepted only after consultation with the microbiologist or pathologist. Pathogens in highest concentration in first morning collections will be diluted by added secretions. There is a high likelihood that samples stored after collection may become overgrown with contaminants. Improved laboratory extraction techniques preclude the need for large volumes of samples.

3. The first early morning sputum and urine samples are the best for recovery of acid-fast bacteria, fungi, and other pathogens. Samples collected at other times are acceptable. Early morning secretions are more concentrated and more likely to contain large numbers o f the etiologic agent.

4. The timing of blood cultures must be determined by the clinical condition of the patient. Physicians should always indicate the collection schedule. Except in acute cases of septicemia, blood cultures should not be drawn more frequently than half an hour apart. A total o f three cultures per 24 h is usually sufficient to diagnose most cases of septicemia.

5. The following specimens should be collected only after consultation with the pathologist or microbiology supervisor and, if tested, the protocol must be published in the standard procedures manual:

• Viral cultures
• Darkfield examinations for spirochetes or other bacteria
• Special blood cultures for recovery of fungi or cell-wall-deficient “ L” forms
• Recovery of chlamydia, rickettsia, leptospira, or other unusual organisms
• Blood for serum-killing power tests or antibiotic drug assays

These situations often need the use of special laboratory equipment and selection of enriched or selective media. Samples often must be collected at specific times or in special ways in order to ensure optimal recovery of microorganisms, or to produce results which can be interpreted in relation to therapeutic regimes. Physicians must bear the responsibility of informing the laboratory that an unusual infectious disease is suspected. If the physician or someone in the ward is to obtain the specimen, laboratory personnel should be consulted to determine the need for any special techniques or collecting devices

(d) Specimen collection procedures

1. All specimens should be obtained in appropriate sterile containers. If samples are to be delayed in processing or are sent to reference laboratories, transport medium should be used. If the container is not sterile, results may be erroneous. It is the laboratory responsibility to see that sterile containers of suitable construction are made available to physicians or ward personnel. Containers for stool cultures should be clean but need not be sterile.

2. Anaerobic cultures are best collected by aspirating abscess fluid with a sterile syringe and needle. Syringes can be capped with the needle holder and submitted for culture. If swabs are used, they must be placed immediately into gassed tubes or suitable anaerobic packets. It is important to protect species of anaerobic bacteria from the killing effect of atmospheric oxygen. The chance for recovery is enhanced by protecting the specimen from any contact with atmospheric oxygen before inoculation in the laboratory.

3. Sputum samples should contain lower respiratory secretions. Patients should be directed to cough deeply. Habitual smokers understand well what a deep cough means. The mouth should be rinsed with water or gargle, and dentures should be removed immediately before the sample is collected. All sputum samples are contaminated to varying degrees with oropharyngeal secretions. Mechanical rinsing o f the mouth immediately before expectoration will reduce the number o f contaminating bacteria. Induced specimens or transtracheal aspirations are recommended for patients who cannot produce sputum.

4. Bronchial washings must be processed as soon as possible after they are obtained. Currently, there is no documentation to support the use of an enrichment medium for delayed transport of such specimens for isolation of M. tuberculosis. Some microorganisms which may infect the respiratory tract, such as Haemophilus influenzae, are susceptible to drying on low temperatures. M. tuberculosis specimens should be mailed “unenriched” to a reference laboratory. An in-transit decontaminating solution developed at CDC has not been tested with bronchial washings but has successfully preserved M. tuberculosis/sputum specimens for days while killing most contaminating organisms.

5. The collection of clean-catch urine samples should not be left to chance. Ideally, the specimen should be collected by the patient after specific instructions by a nurse or aide. There is a high potential for contamination o f the periurethral area in females from vaginal or bowel flora. Since most laboratories perform routine colony counts on all urine samples, meticulous care must be taken in specimen collection if valid results representative of bladder urine are to be obtained.

Note: if patients are to collect specimens unattended, specific verbal and written directions will help to ensure collection of a good specimen. It may be well to actually read the instructions to the patient, particularly if there is a language barrier. It is recommended that these instructions be printed on a card for the patient to retain during the collection procedure. Instructions should be available in the predominant languages o f the area.

6. Stool specimens sent for the recovery of acid-fast bacilli should not be processed.

Note It is virtually impossible to recover acid-fast bacilli from fecal material because of the inability to prevent heavy overgrowth with bowel flora.

7. Surface lesions (wounds) must be sampled carefully. It is imperative that the surface lesion be opened and the advancing edge of the lesion firmly sampled. Pus must be expressed onto swab. Surface lesions are unsuitable for anaerobic studies.

Note: Pus, alone, may not show growth upon plating since the encased organisms may be dead. The REPRESENTATIVE specimen is at the advancing margin of the wound. Do not submit a dry swab that has been carelessly rubbed over a surface lesion. Anaerobes are abundant on skin surfaces and are common surface wound contaminants. Scrub the area around the wound carefully before  sampling.

8. Wound specimens sent for anaerobic workup should be submitted in an appropriate anaerobic transport medium or in the syringe used to collect an aspirate.

Note: Anaerobic transport media are made to protect the strictest anaerobe. Other methods of transport may preserve some anaerobes for a time but may not allow optimal recovery o f anaerobes.
The physician’s need for complete anaerobic data is no less than that of the laboratory for a properly selected and submitted specimen in anaerobic transport.

9. Descriptive terms like “ wound,” “ eye,” “genital,” or other nonspecific terms are not as helpful to the laboratory as are specific anatomic locations describing the source of specimens
along with a diagnosis.

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