Detection of Bence-Jones protein in practice.

Abstract

The monoclonal gammopathies are characterized by the presence in serum and/or urine of a monoclonal, intact immunoglobulin or fragment, a so-called monoclonal component, produced by a B-cell clone that has undergone a genetic transformation. The clinical conditions accompanying monoclonal components encompass a wide spectrum, ranging from an entirely asymptomatic non-progressive state, usually detected incidentally, through to a malignant, aggressive multiple myeloma or lymphoma (see Table 1). The particular presentation of a monoclonal gammopathydepends on the exact transformation of the cell and the nature of the monoclonal component produced which may itself exhibit deleterious biological properties (see Table 1). An important part of the investigation of patients with suspected monoclonal gammopathy or a proven serum monoclonal component is the detection of urinary Bence-Jones protein (BJP), a monoclonal immunoglobulin light chain. This is for a variety of reasons. Firstly, the detection of a monoclonal component is central to the diagnosis of myeloma, and between 14% and 20% of cases of myeloma are characterized by BJP as the only monoclonal component. Secondly, it was observed in early studies that the presence of BJP was highly predictive of a malignant monoclonal gammopathy. Despite the occasional reports of cases classi®ed as monoclonal gammopathy of undetermined signi®cance excreting BJP of up to 1 g/24 h, the presence of BJP is today regarded as central to the initial assessment of the patient presenting with a serum monoclonal component. It is also important in assessing prognosis and directing subsequent management of a patient with a serum monoclonal component in whom the initial diagnosis is uncertain. Thirdly, in those conditions arising from deposition of aggregates of monoclonal light chains ± AL amyloidosis and light chain deposition disease ± detection of urinary BJP may provide an important pointer to the presence of the disease and subsequent investigation and, for AL amyloidosis, early treatment. The importance of the detection of urinary BJP is thus not in doubt. However, a recent survey by the UK National External Quality Assessment Scheme (NEQAS) for monoclonal protein revealed uncertainty as to the desired detection limit for BJP and, partly as a consequence of this, a subsequent distribution indicated that 35% of laboratories were unable to detect BJP at approximately 60mg/L. There Personal View Ann Clin Biochem 2000; 37: 563±570