Diagnostics Figure 1: The Salivax™ HIV Device
Saliva filtration assembly, reagents A and B and test device. Table 1: Tabulation of Results Results
POS Salivax™
POS NEG
TOTAL
427 (a) 2 (c)
Biorad®/LabWest EIA NEG 2 (b)
761 (d) 429 (a+c) TOTAL
429(a+b) 763(c+d)
763 (b+d) 1192*
*Eight samples with inconclusive results were not used in the calculations. NEG = negative; POS = positive.
antigens is immobilised on a binding membrane. A special filter consisting of coarse filter foam as well as a non-binding pre-filter is used to separate large particulate matter and viscous fibrous matter from the saliva followed by a hermetically sealed composite filter to remove the smallest of debris. In order to facilitate filtration, a threaded plunger is used to exert moderate (30 lb) pressure. The patient sample is filtered and it flows through the membrane. As it flows through, antibodies in the sample, if present, react with the antigens immobilised on the membrane. The antigens used are proprietary recombinant antigens with multiple epitopes on a polypeptide of various different HIV-1 and HIV-2 strains. The non-reacting portion of the specimen is removed by the sample containing a wash buffer (reagent A). Next, a reagent consisting of goat anti-human IgG conjugated to colloidal gold (reagent B) is applied. The conjugate binds to human antibodies (lgG) attached to the antigens on the membrane. Within minutes of this step the results appear on the membrane. There is also a control area on the membrane that will react with the reagents to form a control dot showing that the test is functioning as designed. Two dots approximately 2 mm in diameter indicate an HIV-reactive or -positive specimen. When all of reagent B flows through, the test is read.
Method
glands but at a much lower concentration (approximately 1/800th) than in serum.36
potential marker for HIV infection in infancy37 disease stage.38
HIV-specific IgA in saliva has been reported to be a and may correlate with
However, it is unclear whether the specific anti-HIV IgA detected in saliva is secretory IgA or serum IgA from CF. It follows that if specific secretory antibodies are to be detected in whole saliva, conjugates must be employed that can identify IgA. However, the predominant immunoglobulin in whole saliva and CF is IgG and current tests incorporate anti-IgG conjugates.
Whole saliva receives variable amounts of IgG from the transudation of capillary fluid. IgG levels appear to be independent of flow rate and probably originate from local plasma cells and CF; thus, CF appears to be the main source of salivary IgG.8
of CF is approximately four times lower than in blood.36,39
However, the IgG concentration Preliminary
data indicate that IgG levels do not decline and HIV antibody titres and Western blot intensities remain consistent when up to five sequential oral fluid samples are collected using a device. The stability of IgG in the presence of other oral fluid constituents (i.e., enzymes) is most probably due to the chemical stabilisers in the transport medium included with the collection devices. Efforts should be made to avoid the collection of sputum when attempting to collect saliva.40
The Salivax™ HIV Device The Salivax™ HIV test device (see Figure 1) is manufactured by ImmunoScience, Inc. In the test, a mixture of specific HIV-1 and 2
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Subjects were selected from volunteers at six local clinics in the San Francisco Bay Area. Each subject gave informed consent as required under applicable laws. The university institutional review board (IRB) had approved the protocol and the informed consent. From each subject, 5 ml of saliva and 1 ml of serum was collected. Saliva samples were collected in a low-binding plastic aliquot tube after each subject had abstained from smoking, chewing, eating or drinking anything for at least 15 minutes and had kept their mouths well hydrated. Serum samples were collected using conventional Becton-Dickinson® Vacutainer® apparatus. Each sample pair was identified by a unique number. When necessary, for transporting, the samples were transported in ice or refrigerated prior to analysis. Each saliva sample was subjected to the Salivax HIV test according to its package insert and each serum sample was tested using US Food and Drug Administration (FDA)-approved Biorad® enzyme immunoassay (EIA), at LabWest, Inc., a College of American Pathologists (CAP)-certified clinical laboratory. The saliva and serum tests were carried out in separate locations and the results tabulated centrally. Two different batches of Salivax HIV test kit, COM003052410 and COM0003041510, were used in the study.
A total of 1,200 serum and saliva sample pairs were collected. Eight samples either had inadequate volume or produced an inconclusive result and were not included in the final tabulation. The saliva samples were tested using Salivax HIV test devices and the operators found them to be simple and easy to use.
Results
The term validity refers to the extent to which the test accurately detects what it purports to; in other words, the ability of the test kit to detect HIV-infected cases and to show as negative those that are not. Validity has two components: sensitivity and specificity.41
To calculate sensitivity and specificity, the data concerning the subjects and the test results can be put in a 2 x 2 table (see Table 1).42
EUROPEAN INFECTIOUS DISEASE
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