Dissociation of hepatitis B surface antigen (HBsAg) from immobilised anti-HBsAg antibody in a two site immunoradiometric assay: its relevance to hook effect and recycled assay

Development and validation of a hepatitis B virus DNA sequencing assay for assessment of antiviral resistance, viral genotype and surface antigen mutation status

The objective of this study was to develop a DNA sequencing assay that examines sensitively and reliably all conserved domains of the reverse transcriptase-encoding region of the HBV genome for antiviral resistance-associated mutations while simultaneously producing ample information for precise genotyping and determination of HBsAg mutation. This assay was used to examine 1000 de-identified HBV DNA positive samples with known viral loads from a broad-based, unselected patient population from across the United States. Of these, 946 were assayed successfully. Antiviral resistance-associated mutations were identified in 104 samples. The escape mutation sG145R in the surface antigen was identified in 0.8% of patient samples. Infections with genotypes A, B, C, D, E, F, G and H were observed in 36.6%, 19.6%, 21.7%, 13.5%, 3.6%, 0.7%, 2.2%, and 0.5% of patient samples respectively. Fifteen samples (1.6%) appeared to harbor infections with multiple genotypes as shown by the presence of double peaks throughout sequence electropherograms. The limit of detection of this assay was approximately 150IU/mL.

HBsAg blood screening and diagnosis: performance evaluation of the ARCHITECT HBsAg qualitative and ARCHITECT HBsAg qualitative confirmatory assays

A low initial reactive rate for screening assays is important for time- and cost-effective infectious disease testing. Therefore, the new ARCHITECT HBsAg Qualitative screening assay, in conjunction with the new ARCHITECT HBsAg Qualitative Confirmatory assay, was introduced. As the role of hepatitis B surface antigen (HBsAg) as surrogate marker for HBV resolution and the monitoring of drug effectiveness are becoming increasingly important, the established ARCHITECT HBsAg Quantitative assay remains available on the market. Precision, sensitivity, and specificity of the newly developed screening assay were in the range of established HBsAg assays. Seroconversion sensitivity was slightly superior compared to other commercially available assays. An initial reactive rate of 0.2% (without HBsAg-confirmed positive samples of 0.17%) for the ARCHITECT HBsAg Qualitative assay was observed. As the new screening assay is a 1-step assay format, the "high-dose hook effect" was investigated to assess the risk of false-negative results, but even very high positive HBsAg samples obtained signals clearly above the cutoff.

Medical virology in Malaysia

Virology is a branch of biological science dealing with the study of viruses, and medical virology focuses on the study and control of diseases due to viruses that is of medical importance. The development of medical virology in Malaysia has its beginning in the Institute for Medical Research (IMR), following the establishment of the Division of Medical Zoology and Virus Research in the institute on 23 March 1953. The second institution in the country to establish diagnostic and research work in medical virology was Department of Medical Microbiology, Faculty of Medicine, University Malaya. This was followed by University Kebangsaan Malaysia, University Sains Malaysia and University of Sarawak Malaysia. The National Public Health Laboratory (NPHL) is the latest institution to establish a laboratory in 2003 for virus isolation and services to support country surveillance and outbreak investigation of infectious diseases due to viruses. In the field of medical virology, Malaysia contributed substantially in the areas of virus diagnostic services, development and research ranging from survey and documentation on the existence and prevalence of viruses causing diseases in Malaysia, clinical presentation and epidemiological features of virus diseases, evaluation of new diagnostic tests to pathogenesis of viral diseases. Malaysia contributed to the discoveries of at least 12 new viruses in the world. ASEAN plus Three (China, Japan, Republic of Korea) Emerging Infectious Programme was established to overcome the challenges and impact of emerging and re-emerging infectious diseases in this region. Malaysia as the co-ordinator of the laboratory component of the programme, contributed to strengthen the regional laboratory capability, capacity, laboratory-based surveillance and networking. The future of medical virology in Malaysia in terms of integration of diagnostic, reference and research to support the country’s need will be enhanced and strengthened with the on-going development of the National Centre for Disease Control and Prevention (CDC Malaysia) which also incorporates a futuristic Special Diagnostic and Reference Laboratory.

"Hook effect" in prolactinomas: case report and review of literature

OBJECTIVE

To present a case of the "hook effect" occurring in the prolactin immunoassay in a patient with giant prolactinoma and to review this phenomenon.

METHODS

We describe the clinical, biochemical, radiologic, and pathologic data of a patient with a giant prolactinoma, in which dilution testing of serum prolactin levels confirmed the presence of the hook effect. We discuss the historical and mechanistic aspects of the hook effect and then review its occurrence with the prolactin assay.

RESULTS

A 65-year-old man sought medical attention because of headaches, personality changes, and "bulging" eyes. Cranial magnetic resonance imaging disclosed a 10-cm-diameter, lobulated, heterogeneous, locally invasive mass in the anterior skull base and cranial fossa. Initial laboratory testing showed a prolactin level of 164.5 ng/mL (normal range, 1.6 to 18.8). The pathology specimen from his surgical debulking procedure was consistent with prolactinoma. Retesting of the original serum prolactin sample with serial dilutions revealed a prolactin level of 26,000 ng/mL. A postoperative diluted prolactin level was 22,000 ng/mL. Both prolactin samples demonstrated the hook effect. Dopamine agonist therapy was initiated, and the prolactin level and size of the tumor decreased substantially. The hook effect most commonly occurs when excess antigen (for example, prolactin) is present during testing. Dilution testing can counteract this assay phenomenon.

CONCLUSION

Clinicians should be aware of this laboratory phenomenon when evaluating large pituitary or parasellar masses. When the hook effect is suspected, dilution testing of prolactin samples may prevent incorrect diagnosis and unnecessary surgical intervention in patients with prolactinomas.