A Guide to Specimen Management in Clinical Microbiology

SECTION II Specimen Management Policies
and Rationale

In cooperation with selected members of the medical staff or laboratory clients, the laboratory should formulate a policy for specimen management that supports both good medicine and good laboratory practice. This policy should be documented, and a copy of it should be distributed to all users and clients of microbiology laboratory services. Part of the policy should be a carefully prepared, fact-supported manual on how to collect and handle specimens. It is important for nurses and clinicians to understand the needs of the laboratory regarding specimen collection and handling. In addition, the policy should address the special needs of the laboratory and the rationale for these needs. Laboratory leaders should be prepared to provide in-service training on specimen collection and management policies to medical and nursing staff and others who collect specimens for microbiology. This section discusses simple policy statements and includes the rationale for each policy in italics.

Collection Times

Include the time of specimen collection on the requisition. Without it, one may not be able to interpret results.

Patricia Charache, Ph.D., (D)ABMM

(Deceased)

1.The optimal times for specimen collection must be based on both the type of infectious disease process and the ability of the laboratory to process samples. Laboratories are usually better staffed and therefore better able to receive and process specimens during the daytime hours.

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 and report urgent specimens during "off" hours, and consultation with supervisory personnel is highly recommended.

2.Twenty-four-hour specimen collections for culture should be discouraged, and such collections should be accepted only after consultation with the microbiologist or pathologist.

Pathogens that appear at their highest concentration in first morning secretions will be diluted by added material.

Stored samples are very likely to be overgrown with contaminants. Improved laboratory culture techniques preclude the need for large volumes of samples.

3.First early-morning sputum and urine samples are optimal for recovery of acid-fast bacteria, fungi, and other pathogens in adults. Samples collected at other times are acceptable.

Early-morning secretions are more concentrated and therefore more likely to contain large numbers of the etiologic agent.

Children under 7 years of age cannot reliably collect early-morning specimens. The majority of specimens from this age group are randomly collected, and therefore there are circumstances where collection on three consecutive days may be required to optimize retrieval of organisms, especially from gastric aspirates.

First morning urine specimens from children who are not toilet trained are probably no better than randomly collected specimens.

4.The timing of blood cultures should be determined by the clinical condition of the patient. Physicians should always indicate the collection schedule. A maximum of three cultures per 24 h is usually sufficient to diagnose most cases of septicemia. Newer culture systems and culturing of larger blood volumes may reduce the number of cultures needed. In many cases, two draws from two separate sites obtained at the same time may be adequate.

In endocarditis, typhoid fever, brucellosis, and other uncontrolled infections, bacteremia is continuous, and thus the timing of collection is less critical. In other infections, bacteremia is intermittent and may precede the onset of fever by an hour, making collection timing important.

In acute febrile episodes, two draws of at least 10 ml of blood each from separate venipuncture sites allow immediate initiation of therapy. The recovery rate after three negative cultures per 24 h is extremely low except in cases in which a sudden fever spike is observed; then, drawing of an additional blood sample may be indicated.

In pediatric populations, the collection of more than one blood culture in a 24-h period is determined by the size of the child and access to a suitable collection site. A volume of =0.5 ml is acceptable, although 1 to 5 ml from children younger than 5 years old is desirable. Refer to the manufacturer's recommendations for adequate collection volumes.

Small volumes of blood from children should never be rejected. Notify the physician that a delay in detection may be anticipated because of the small volume cultured.

5.Unless the laboratory routinely processes such specimens in-house, the following procedures should be done only after consultation with the pathologist or microbiology supervisor, and if the specimens are to be tested, the protocol should be published in the procedures manual.

a.Viral cultures, unless the tests are done routinely. Many viral specimens are now routinely tested by nucleic acid amplification and culture is seldom done in community hospitals.

b.Tests of serum-killing power or antibiotic assays of blood

c.Dark-field examination for spirochetes or other bacteria

d.Special blood cultures for recovery of fungi

e.Recovery of Chlamydia, Rickettsia, Leptospira, or other unusual organisms

f.In pediatric patients, testing for Bordetella pertussis, respiratory syncytial virus antigen detection, rotavirus antigen detection, and blood culture for Malassezia furfur.

These requests often require the use of special laboratory equipment and the selection of enriched or selective media not routinely stocked in the laboratory. Nucleic acid tests are now used routinely by many facilities or are available at reference laboratories.

Samples often must be collected at specific times or in special ways to ensure optimal recovery of microorganisms or to produce results that can be interpreted in relation to therapeutic regimens.

Physicians bear the responsibility for informing the laboratory that an unusual infectious disease is suspected. Laboratory personnel should be consulted to determine whether any special techniques or collecting devices will be needed.

Collection Procedures

Obtaining a good specimen is the clinician's responsibility. Generating good test results is the laboratory's responsibility. When these are combined, a negative test can be as helpful as a positive one.

Eileen M. Burd, Ph.D., D(ABMM)
Emory University Hospital, Atlanta, GA

1.All specimens must be collected in appropriate sterile containers. If samples will be delayed in processing or are being sent to reference laboratories, a transport medium must be used.

If the container is not sterile, results may be erroneous. It is the responsibility of the laboratory to see that sterile containers of suitable leakproof construction are made available to physicians or ward personnel.

Specimens for viral testing should be available and the manufacturer's instructions must be followed for using the collection apparatus and the viral transport medium.

2.Samples for anaerobic cultures are best collected by aspirating abscess fluid with a sterile syringe and needle and then injecting the aspirated fluid into an anaerobic transport vial. Although not a method of choice, syringes (with the needle removed and discarded) can be capped with the needle cover and submitted for culture. The submission of swabs for anaerobic culture is discouraged, but if they must be used, they should be immediately placed in suitable anaerobic transport packets and pushed into the agar plug.

It is important to carefully protect species of anaerobic bacteria from the killing effects of atmospheric oxygen and desiccation.

The chances for recovery of an anaerobe are enhanced when the specimen is protected from any contact with atmospheric oxygen, as much as possible, before inoculation in the laboratory.

The incidence of serious anaerobic infections is limited in pediatric populations. In this group it may be important to consider the collection of stool and blood for the diagnosis of infant botulism and food-borne intoxication caused by Clostridium perfringens.

3.Blood, not sputum, may be the specimen of choice for diagnosing bacterial pneumonia. Sputum samples for culture must contain lower respiratory tract secretions as evaluated by Gram stain. The mouth should be rinsed with water or the patient should be asked to gargle; dentures should be removed immediately before the sample is collected. Patients must be instructed to take two to three deep breaths and then cough deeply.

All sputum samples are contaminated to various degrees with oropharyngeal secretions. Expect some sputum specimens to be rejected because of normal oropharyngeal flora detected on the screening Gram stain.

Mechanical rinsing of the mouth immediately before expectoration reduces the number of commensal...