3/19/2019 Show
Blood samples must be drawn by phlebotomists in a specific order to avoid cross-contamination of the sample by additives found in different collection tubes. Phlebotomy order of draw is the same for specimens collected by syringe, tube holder, or into tubes preevacuated at the time of collection. The correct order of draw follows:
The placement of tubes not listed here should take into consideration the potential for their additive to alter results obtained from the next tube if carryover were to occur. Plastic serum tubes containing a clot activator may cause interference in coagulation testing. Only blood culture tubes, glass nonadditive serum tubes, or plastic serum tubes without a clot activator may be collected before the coagulation tube. Numerous errors can occur during the collection and handling of blood specimens, which pose significant and avoidable risks to the patient and the phlebotomist. When global standards are not fully implemented, it is more likely that patients will be injured during the procedure, biologically representative specimens will not be obtained from patients, and test results will not be comparable from one facility to another. CLSI’s GP41 —Collection of Diagnostic Venous Blood Specimens provides a descriptive, stepwise process and procedures reflecting the quality system essentials format for diagnostic venous blood specimen collection. Special considerations for collections from vascular access devices, blood culture collection, and collections in isolation environments are included, as well as how to handle emergency situations. An expanded appendix section provides helpful tips for collecting specimens from pediatric and other challenging patients. ← Go BacksummarySpecimens used for HIV testing
Many types of specimens can be used for biological surveillance of HIV: plasma, serum, whole blood, DBS and oral fluid. The choice of specimen collected depends on the logistics, populations and sites selected, and the HIV testing strategy and algorithm. Specimens must be collected, tested and stored in an appropriate manner in order to obtain accurate and reliable results. For serosurveillance activities, specimens are usually collected and stored prior to HIV testing at a regional or national laboratory. Serum, plasma and DBS can be stored and tested at a later date; specifications for storage will depend on the type of specimen collected. Specimens not tested on site at the local level will need to be transported to a regional or national laboratory for testing. The methods by which specimens are transported will depend on the country’s infrastructure. Few countries may have courier systems linking health-care facilities and laboratories. More frequently, the field surveillance staff members themselves transport the specimens from the local to the national laboratory. However, other options such as public transportation can be explored. 3.1. Selecting specimens3.1.1. Advantages and disadvantages of serum and plasmaHIV testing of serum and plasma, which can be collected by venepuncture (see section 3.2), have the following advantages and disadvantages: Advantages
Disadvantages
3.1.2. Advantages and disadvantages of whole bloodWhole blood, which can be collected by venepuncture or finger-stick (see section 3.2), has the following advantages and disadvantages in HIV testing: Advantages
Disadvantages
3.1.3. Advantages and disadvantages of dried blood spotsDried blood spots can be prepared by collecting venous whole blood or finger-stick whole blood and dropping an amount onto a filter-paper. DBS have the following advantages and disadvantages: Advantages
Disadvantages
3.1.4. Advantages and disadvantages of oral fluidOther specimens besides blood and blood products can be used for HIV testing. For linked testing, where informed consent must be obtained, oral fluid may be used. Advantages
Disadvantages
recommendationBlood (serum, plasma, DBS) is the preferred specimen for testing because it has a higher concentration of HIV antibodies than oral fluid. It also allows for additional testing, including for syphilis, hepatitis B and hepatitis C, and for special studies of HIV type and subtype, and ARV resistance. 3.2. Collecting, processing and storing blood, serum and plasma specimensbloodBlood needed for an HIV test can be collected either by venepuncture (whole blood, serum, plasma) or by finger-stick (whole blood). 3.2.1. Processing blood collected by venepunctureTo collect blood by venepuncture, follow local clinical or laboratory procedures. See the Appendix and Section 6.3 for information on safety procedures. The following steps are recommended for processing blood collected by venepuncture20: Collect up to 10 ml of blood from the patient’s vein into a sterile 10 ml tube.
3.2.2. Storing serum and plasma collected by venepunctureTo store serum and plasma, consider the following: 22, 23
3.2.3. Collecting blood by finger-stickBlood collected by finger-stick can be used to perform rapid tests or make DBS on filter-paper. A DBS may be preferred in rural and non-clinical settings, which often do not have trained phlebotomists or laboratory facilities with appropriate equipment (e.g. centrifuges).
3.2.4. Preparing and storing a dried blood spot for an HIV testBlood from a finger- or ear-lobe stick can be used to make DBS.24 Although finger-stick is the most typical method, DBS can also be obtained by using blood collected in a tube with an anticoagulant.25 DBS have the advantage of being easy to transport, without the need for a cold chain.
3.3. Collecting and storing oral fluid3.3.1. Collecting oral fluidFor specimen collection, follow test instructions as part of a standard operating procedure. Oral fluid collection devices are available and may be used, if indicated. Some rapid test devices contain an oral fluid collection pad at one end which facilitates collection and testing. See Section 6.3 for information on safety procedures. Oral fluid can only be used with certain EIAs and rapid tests designed for oral fluid specimens, such as the OraQuick brand. Additional rapid tests using oral fluid are currently under field evaluation. The following are the general steps for collecting a specimen:
Due to the complexity of the test, oral fluid specimens collected for EIAs are sent to a laboratory performing EIAs for analysis. 3.3.2. Storing oral fluidOral fluid specimens should be stored at 4 °C for a short period of time. They should be refrigerated during shipment. Specimens should be frozen (–20 °C or below) if stored for an extended period of time. Once thawed, they can be refrozen once. Consult the test kit insert prior to testing for more specific storage information. 3.4. Labelling and recording collected specimens3.4.1. Labelling specimensThe plastic tube, cryovial or filter-paper containing the specimen must be labelled with a specimen code at the time of collection and processing. If labels are used, make sure the label is placed on the side of the tube, not on the cap. Pre-printed cryolabels designed to adhere during freezer storage should be used when specimens are stored in cryovials. It is important that freezing does not affect the visibility of the printing on the label. Surveillance coordinators should provide the field staff responsible for specimen collection with a series of labels or permanent markers and the codes to be used. For unlinked anonymous testing, label the tube only with a new specimen code unlinked to personal identifying information (see Figure 2.1). 3.4.2. Recording specimens and test resultsA separate laboratory logbook or line-listing for surveillance activities should be maintained to record HIV test results by the corresponding code. The logbook should be accessible only to laboratory and surveillance staff; it should be secured in a locked drawer or cabinet when not in use to ensure confidentiality of the persons’ test results as well as their participation in surveillance activities (see Figures 2.1, 2.2). For unlinked anonymous testing, the logbook or line-listing should contain only the new specimen codes and corresponding HIV test results; no personal identifying information on the patients whose specimens are tested should be included. HIV test results can be matched by the new specimen code to the demographic information abstracted earlier on the surveillance form (see Figure 2.1). Which tube would be best for collecting a specimen for a status that must be performed on serum?The needle gauge is used for autologous blood collection. Tube holders with needles attached be disposed of as a unit. This would be the best tube for collecting a STAT test that must be performed on serum.
Which of the following tubes will yield a serum sample?Serum is usually collected in mottled red/gray, gold, or cherry red-top tubes, and red-top tubes are occasionally used.
Which of the following blood collection tube tops would contain a serum separator gel?Gold-top serum separator tube (SST)
This tube contains a clot activator and serum gel separator – used for various chemistry, serology, and immunology tests.
Which tube would typically be used to collect plasma for a stat chemistry specimen?Ch 7 Review. |