In the context of a clinical laboratory, the terms "sample" and "specimen" are often used interchangeably, but they can have slightly different meanings:
1. Sample: A sample refers to a portion or small amount of material taken from a larger source for testing or analysis. In the laboratory setting, a sample can refer to a variety of materials, such as blood, urine, tissue, or other bodily fluids.
2. Specimen: A specimen is a specific type of sample that is collected for laboratory analysis. It is typically a sample that is collected from a patient or subject to diagnose a medical condition or monitor treatment. Specimens can include blood, urine, saliva, tissue, sputum, or other bodily fluids.
In general, a sample is a broader term that can refer to any material taken for testing, while a specimen specifically refers to a sample collected for medical or diagnostic purposes. Both terms are commonly used in the clinical laboratory setting to refer to the materials that are analyzed to provide information about a patient's health.
The first step in the process of the sample is the request for testing. The laboratory must make available a test request form that specifies all the information that will be needed for proper handling and reporting.
Essential information for the test request form includes:
• patient identification;
• tests requested;
• time and date of the sample collection;
• source of the sample, when appropriate;
• clinical data, when indicated;
• contact information for the health care provider requesting the test.
STANDARD PRECAUTIONS
The infectious agent(s) of any biological specimen remains unknown until laboratory diagnosis are carried out. It is therefore difficult to know which sample might be infectious at the time of handling and processing. Thus all patient and laboratory specimens are treated as infectious and handled according to “standard precautions.” Standard precautions are guidelines prescribing ways of avoiding contact with patients' bodily fluids through the practice of good hygiene, such as hand washing and the correct usage of appropriate PPEs, correct handling of hypodermic needles and sharp objects as well as general aseptic techniques.
Additional precautions on the other hand are used as extra measures when handling patients or specimen known or suspected to have an infectious condition, the type of prescribed measures often depend on the infection control need for the infectious agents. Specific infection control needs can be found in the section of Biosafety in Microbiological and Biomedical Laboratories for additional specific precautions for preventing laboratory-acquired infections (LAI) and recommendations for the management of exposure to all infectious diseases.
SAMPLE COLLECTION
Consider the following when preparing instructions:
• Patient preparation—Certain tests may necessitate patient fasting. Timing specifics are crucial for tests like blood glucose, drug levels, and hormone tests.
• Patient identification—Accurate patient identification by the sample collector is vital. This can involve patient questioning, querying a family member, or utilizing an identifying wristband or similar device.
• Sample type—Blood tests may need serum, plasma, or whole blood. Other tests might require urine or saliva. Microbiology tests encompass various sample types, necessitating clear instructions on sample requirements.
• Container type—The sample container is significant, impacting volume and potential additives like anti-coagulants and preservatives. For containers like Vacutainer® tubes that don't regulate volume, clear specifications are essential. Certain microbiology samples might need specific transport media for microorganism preservation.
• Sample labeling—Detailed instructions on sample labeling during collection must be provided.
• Special handling—Certain samples may require special treatment like immediate refrigeration, light protection, or prompt delivery to the lab. Any crucial safety precautions should be outlined.
Patient samples are sometimes collected by the patient themselves, for example, faecal parasitology samples. It is important that the laboratories have set protocols to ensure that appropriate collection kits with instructions for collection, safety precautions, and labeling are available for their patients.
The following rules should apply:
i. Develop and use SOP
ii. Ensure patients are adequately prepared for sample collection
iii. Separate collection from testing area
iv. Ensure appropriate use of PPEs
v. Conduct Training and re-training of laboratory personnel involved in sample collection and processing
vi. Ensure proper waste management guidelines
vii. Ensure provision of all materials needed for sample collection
ORDER OF BLOOD DRAW
When a patient presents with multiple Laboratory investigations, blood must be drawn in a specific order to avoid cross-contamination of additives between tubes. The order described below should be considered as part of proper management of the specimen:
1. Blood culture sample: Blood cultures are used in microbiology. The additive it uses is a broth mixture that is intended to preserve the quality of microorganisms.
2. Coagulation studies (Sodium Citrate tubes): Coagulation tubes have a light blue-colored stopper and a sodium citrate additive.
3. Plain tubes (Red cover vacutainers – No Additive): This is commonly used for laboratory tests that require a serum sample.
4. Clot Activator tubes: Tubes with clot activator cause blood clots and help in separating the serum by centrifugation. This process is often used in the blood bank (cross-match), chemistry, immunology, and serology.
5. Serum separator tube /Gel tubes: SST does not have any additive but a clot activator that will separate blood from the serum by centrifugation. This draw is used in chemistry, immunology, and serology.
6. Lithium Heparin (green cap vacutainer tubes): Tubes with green tops have lithium heparin anticoagulant and are useful for chemistry tests that require the use of plasma samples.
7. EDTA tubes: The EDTA anticoagulant in tubes with a lavender or purple stopper helps remove calcium by forming calcium salts. This draw is often used in blood bank cross-matching and haematology.
8. Sodium Fluoride tubes: Tubes with gray-colored stopper contain sodium fluoride additives, which act as an antiglycolytic agent that helps preserve glucose for up to five days.
ORDER OF DRAW BLOOD SAMPLE
1. Draw blood with a needle and syringe
2. Remove the needle and discard it in a sharps container
3. Dispense the blood into the appropriate container
Procedures should be described for all testing fields in the laboratory covering samples collected in Histology/cytology, Medical microbiology, Haematology, Clinical Chemistry, Genetics, etc…
In clinical laboratory settings, specimens for bacterial culture refer to samples collected from patients that are used to grow and identify bacterial pathogens. These specimens are crucial for diagnosing bacterial infections and determining the appropriate treatment.
Common types of specimens for bacterial culture include:
1. Blood: Blood cultures are collected to detect bacteria in the bloodstream, which can indicate systemic infections such as sepsis.
2. Urine: Urine cultures are used to identify bacteria causing urinary tract infections (UTIs).
3. Sputum: Sputum cultures are collected from the respiratory tract to identify bacteria causing respiratory infections such as pneumonia.
4. Wound swabs: Swabs of wounds or skin lesions are taken to identify bacteria causing skin infections.
5. Cerebrospinal fluid (CSF): CSF cultures are collected to detect bacteria causing meningitis or other central nervous system infections.
6. Stool: Stool cultures are used to identify bacteria causing gastrointestinal infections.
Proper collection and handling of specimens for bacterial culture are essential to ensure accurate results. The laboratory will process the specimen by inoculating it onto appropriate culture media and incubating it to promote bacterial growth. Once bacterial colonies have grown, they are identified using various methods, such as biochemical tests or molecular techniques.
The results of bacterial cultures help healthcare providers determine the most effective antimicrobial therapy for treating bacterial infections. It is important for healthcare providers to collect specimens correctly and promptly send them to the laboratory for analysis to ensure accurate and timely results.
SAMPLE LABELING
Each sample must be clearly labeled with:
• the patient’s first and last name;
• a unique identification number – this could be a hospital number or a number assigned by the laboratory;
• the requested test;
• the date and time of collection;
• the initials of the sample collector.
SAMPLE TRANSPORT
Samples should be transported according to safe transport of infectious/exempt substances guidelines.
SAMPLE RECEIVING, HANDLING, AND RECORDING
The Medical Laboratory shall:
ii. Ensure that all samples and requests received are checked and acknowledged receipt by the laboratory staff
iii. Develop and document criteria for acceptance and rejection of primary samples
iv. Ensure that all samples and requests are screened using the following procedures for acceptance of the request –
a. Correctly match the two personal identifiers between the sample and the request form for the laboratory test (electronic or manual);
b. Ensure that the appropriate sample container is used
c. Ensure that there are no other reasons for rejection of the primary sample
v. Ensure that all rejected requests are recorded, and the authorized requestor informed
vi. Ensure that all samples and requests received are recorded. The date and time of receipt of the sample as well as the identity of the receiving officer shall be recorded.
vii. Ensure that all secondary samples are adequately labeled for ease of traceability to the primary sample (when separation of the sample is required)
viii. Ensure that all samples are safely stored under conditions necessary to maintain sample integrity and proper labeling.
ix. Store or Dispose of leftover samples in accordance with the relevant regulations
x. Ensure that Standard Precautions are observed at all times
The following are examples of samples that should be rejected:
• unlabeled sample;
• broken or leaking tube/container;
• insufficient patient information;
• sample label and patient name on the test request form do not match;
• hemolyzed sample (depending on test requested);
• non-fasting samples, for tests that require fasting;
• sample collected in wrong tube/container; for example, using the wrong preservative or non-sterile container;
• inadequate volume for the quantity of preservative;
• insufficient quantity for the test requested;
• prolonged transport time, or other poor handling during transport.
Record the reason for rejection in the log book and include all pertinent information.
REGISTER OR LOG OF INCOMING SAMPLE
The register should include:
• date and time of collection;
• date and time the sample was received in laboratory;
• sample type;
• patient name and demographics, as required;
• laboratory assigned identification (e.g., number 276_01_06_2009);
• tests to be performed.
PROCESSING OF WHOLE BLOOD INTO PLASMA / SERUM
Serum or plasma should be separated from red blood cells as soon as possible, with a maximum limit of TWO HOURS from the time of collection recommended. A contact time of less than two hours is recommended for Glucose, potassium, Viral load, ACTH, cortisol, catecholamines, lactic acid, and homocysteine.
ANALYSIS OF SAMPLES
The Medical Laboratory shall ensure that samples are tested using validated procedures.
SAMPLE STORAGE
Written policies should be developed to include:
a) Description of samples to be stored
b) Retention time
c) Location for easy access
d) Storage conditions (atmospheric and temperature requirements)
e) Storage organization system (e.g., storing by day of receipt or accession number)
SAMPLE RETENTION
Establish a lab policy for retaining each sample type. Some samples can be discarded quickly, while others may need longer retention. Regularly monitor stored samples and avoid keeping them longer than necessary due to limited refrigerator and freezer space. Monitor freeze/thaw cycles as samples may degrade under these conditions.
Planning is necessary for samples requiring long-term storage. An organized, accessible system using computer tracking would be beneficial. Review the inventory of stored samples at specified intervals to determine when to discard them.
SAMPLE REFERRAL
When sending samples to other labs for testing:
a) Obtain detailed procedures from each lab
b) Ensure correct labeling and container for the sample, along with a requisition form specifying the required test(s) and the sending lab's contact information
c) Monitor referred samples closely:
d) Keep a record of all tests/samples referred, date of referral, and the person referring the test
e) Record and report results received for each referred sample
f) Monitor turnaround times and document any issues encountered
SAMPLE DISPOSAL
The lab must ensure safe disposal of all lab waste. For proper disposal of patient samples:
a) Develop a disposal policy
b) Adhere to local and national regulations for medical waste disposal
c) Establish and follow procedures to disinfect samples before disposal
Here are some links that may be helpful:
1- OSHA's guidelines on hazardous waste management: https://www.osha.gov/hazardous-waste
2- CDC's guidelines on laboratory biosafety: https://www.cdc.gov/safelabs/resources-tools/medical_waste_management.html
Please note that waste management guidelines may vary depending on the specific regulations in your location, so it is important to consult with local authorities or regulatory agencies for further guidance.