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The diagnosis of human immunodeficiency virus (HIV) infection can occur in two basic settings. If an immediate result is not required, specimens can be sent to a central laboratory, where they are accumulated and tested batchwise. In situations where immediate diagnosis is desirable, an on-site test is necessary. In the latter case, a rapid fingerstick test overcomes any prerequisite processing steps associated with the use of sera. Such a test (unlike dried-blood-spot tests) offers the health care provider a timely result, even in remote locations. Although many serum- or plasma-based rapid diagnostic tests have been described (1-6, 8-11), there have been few reports on whole-blood-based tests. What we describe here is a whole-blood method for the expeditious detection of antibodies to HIV, comparable in simplicity of operation to contemporary tests used by diabetics to measure blood glucose levels.

Specimens. Specimens were collected from patients visiting the Clinical Laboratory Hospital de Infectologia "Dr. Daniel Mendez Hernandez," Centro Medico Nacional la Raza, Instituto Mexicano del Seguro Social, Mexico City, Mexico. All participants gave informed consent, and epidemiological and demographic data were collected; pre- and posttest counseling was offered. Patients were classified as HIV seropositive (i.e., asymptomatic or at identified AIDS stages) or HIV seronegative (i.e., either with other infectious or noninfectious diseases or certain physiological conditions or clinically healthy). Blood was collected from participants by fingerstick (medical lancet) and immediately analyzed with the whole-blood test (WBT) device under investigation. Thereafter, blood was collected by venipuncture into tubes to obtain serum or plasma. An HIV type 1 (HIV-1) low-titer performance panel and seroconversion panels (panels D, E, H, I, J, K [modified], L, M, N, P, Q, R, S, U, V, W, X, Y, Z, AB, AC, AD, and AE, comprised of serum and/or plasma specimens) were purchased from Boston Biomedica, Inc. (BBI; West Bridgewater, Mass.). Enzyme immunoassay (EIA) and Western blot test results were provided along with each panel. A total of 18 HIV-2 serum specimens (13 from the Ivory Coast and 5 from Serologicals, Clarkston, Ga.) were analyzed by approved strategies by using EIA and/or Western blotting (kit from Cambridge Biotech Corp., Worcester, Mass.).

Test device and protocol. The WBT device (Hema·Strip HIV-1/2; Saliva Diagnostic Systems, Inc., Vancouver, Wash.) consists of a pen-like transparent cylinder having a capillary tip. A test strip resides inside the cylinder. A few microliters of blood is taken up by capillary action into the distal tip of the cylinder when a blood droplet contacts it. The distal end is then pressed down through the foil barrier of a provided buffer vial. The force of this action propels buffer into the tip of the cylinder; the blood specimen is thereby mixed with and diluted by the buffer and deposited at the base of the test strip. The WBT device can then be placed upright (for instance, in a rack) or laid down on a flat surface. Within 15 min, via lateral-flow deposition of a chromophore on a membrane, either a single line (control line, indicating an HIV nonreactive specimen) or two distinct lines (a control line and a test line, indicating an HIV reactive specimen) will develop.

Performance. The diagnostic sensitivity of the WBT in this study was 99.4% (six false negatives among 1,018 confirmed positive patients); the specificity was 99.9% (one false positive among 941 noninfected individuals). False negatives occurred in AIDS patients at stages I (n = 3), II (n = 1), III (n = 1), and IV (n = 1) (three of these six WBTs were read as faintly positive at later times). The lone false positive was from a high-risk patient (partner seropositive for HIV) with an indeterminate Western blotting result but with a negative EIA; this patient subsequently (approximately 8 months later) tested positive by both EIA and Western blotting and so may have been in the process of seroconversion. No specific cross-reactivity correlating with any (non-HIV) pathological condition was identified. The clinical conditions (suspected or confirmed) of the noninfected individuals were viral infection (n = 521); bacteriological, fungal, or parasitic infection (n = 68); hematological or renal disorders (n = 51); other diseases or conditions (n = 238), and none (healthy) (n = 63). The sensitivity and specificity for the EIA in this study were 100 and 97.9%, respectively. EIA false positives in this study (20 of 941) were those which gave more than one positive reading (in two or three testings).

Discussion. The sensitivity of the WBT in this study was slightly lower, and its specificity was somewhat higher, than those of the reference method employed (EIA) when used to evaluate serum or plasma specimens in a clinical setting. It fell within the performance range of several commercially available EIAs and Western blotting procedures when used to evaluate seroconversion and low-titer performance panels. This is noteworthy, since immunoglobulin G (and not immunoglobulin M) antibodies are detected by the WBT and since its signal is not enzyme amplified. In one study, the device (foil pouched as a stand-alone kit) maintained good stability and functionality for a year when stored at several constant temperatures, including 45°C (data not shown). In addition, a recent report (7), based upon a test that was otherwise immunochemically identical (3), suggests that the WBT would efficiently detect immune responses to a variety of HIV subtypes.