The presence of antibodies in some patients' serum has long been known to be a potential source of interference in immunoassays, as shown by numerous case reports. These often appear after the introduction of a new analyte (e.g. troponin) and then decrease in number as the topic becomes exhausted. This highlights the persistent and intrinsic nature of this problem, despite attempts by the manufacturers to compensate for this source of error. However, an explanation of the immunoanalytical basis underpinning these assays could be more effective in raising awareness than intermittent case reports. In this review we have outlined the use of antibodies as reagents, the factors determining how they bind to antigen(s), and the nature of the immune response in order to explain the insidious and unpredictable nature of this form of interference. Studies on the prevalence of interference have yielded values ranging from 0.05 to more than 2%. However, these figures are analyte- and assay-specific, influenced by the study design, and are not therefore generally applicable. It is also highly likely that figures on prevalence and incidence will worsen in the future because of the wider use of monoclonal antibodies as diagnostic and therapeutic tools. Clinical laboratories should be alert to assay interference from antibodies irrespective of its nature, as immunoassays will remain an indispensable analytical tool, unlikely to be replaced in the foreseeable future by a practical alternative.

No abstract

Plasma dehydroepiandrosterone sulphate, androstenedione, testosterone (T), dihydrotestosterone (DHT), and sex hormone binding globulin (SHBG) have been measured in 64 females and 26 males aged less than 25 years and with acne vulgaris. Oestradiol was measured in the males. Free T and free DHT were calculated. Acne was graded on three sites and the sebum excretion rate (SER) was measured in most patients. With the possible exception of free DHT, none of the plasma steroids or SHBG correlated with acne severity or with SER. Free DHT in the females showed a possible, but weak, correlation with total acne (r = 0.25, P = 0.07), but comparison with male data showed that this was not causative. The role of androgens in acne is permissive and plasma androgen measurements usually have no place in its management.

AddressesAll immunoassays for female serum testosterone give falsely high results in some samples. The effect is variable and cannot be predicted for any given sample. Inaccurate calibration or interference by cross-reacting substances is almost certainly the cause of the problem, but for many immunoassays, the exact nature of the interferent is not known. Some of the interference can be removed by employing an extraction step prior to immunoassay. The advent of fast simple and sensitive liquid chromatography tandem mass spectrometry methods offers an exciting alternative to immunoassay for serum testosterone measurement. It is recommended that all high serum testosterone concentrations in women are checked, before reporting, by a method which is accurate (i.e. minimal bias to isotope dilution gas chromatography mass spectrometry [ID-GCMS] method) and is not subject to interference. Action should also be taken by assay users, manufacturers, regulators and professional bodies to ensure accurate standardization and comparability of assays. 2007; 44: 5-15 Ann Clin Biochem

SUMMARY The quantitative changes in body hair growth, and sebaceous secretion, as well as plasma sex hormone binding globulin, luteinizing hormone and follicle stimulating hormone, testosterone and androstenedione were measured in a hirsute woman aged 21 years under ‘reverse sequential’ treatment with cyproterone acetate and ethinyl oestradiol. The subject, before treatment, had normal excretion of 17‐oxosteroids, 17‐oxogenic steroids, androsterone, dehydroepiandrosterone and aetiocholanolone. The rate of hair growth on the thigh and the average diameter of the hairs was significantly reduced after only 2 cycles of treatment. After 6–7 cycles the length attained by the terminal hairs was reduced and this appeared to be due mainly to change in growth rate rather than to alteration in the duration of anagen. The shorter and thinner hairs also had a much shorter region of pigniented medulla. A progressive decrease in the extent and continuity of the medulla could be detected after 3 cycles of treatment. Sebaceous secretion was also reduced after 2 cycles of treatment; and there was thereafter steady improvement of the pustular acne. Sex hormone binding globulin levels were low before treatment, unaltered by a first cycle of cyproterone acetate alone, but increased by addition of ethinyl oestradiol. Gonadotrophins remained low throughout, while testosterone and androstenedione levels, initially high, were substantially suppressed.