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Use and Abuse of Eight Widely-Used Diagnostic Procedures in Clinical Immunology: a WHO Memorandum*

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Use and Abuse of Eight Widely-Used Diagnostic Procedures in Clinical Immunology: a WHO Memorandum* Bulletin of the World Health Organization, 59 (5): 717-728 (1981) Use and abuse of eight widely-used diagnostic procedures in clinical immunology: a WHO Memorandum* This Memorandum assesses eight widely-used diagnostic procedures with the aim of establishing their usefulness in patient care. For eachprocedure, the main methods that can be recommended at present are outlined and their pitfalls discussed. For each procedure, recommendations are made as to the clinical conditions for which the test is essentialfor diagnosis, the conditions for which the test will help in assessing and monitoring disease activity, and the conditionsfor which the test is usefulfor research purposes only. The recent expansion of clinical immunology has application of some immunological techniques, with- been accompanied by the introduction of a variety of out detriment to patient care. The present Memor- immunological diagnostic tests in clinical labora- andum is an attempt to define indications for im- tories. Owing to increasing demands from clinicians munological tests. It has been restricted to the analysis for such procedures, their use has often been exag- of eight widely-used diagnostic procedures. gerated and there is a general feeling that a better For each procedure, two aspects have been con- definition of the indications for such tests, made in sidered. First, the main methods currently recom- relation to patients' needs, would be beneficial. mended are outlined and their pitfalls discussed. Obviously, immunological tests, like any other Technical details are not included since they are diagnostic tests, can be graded according to their use- readily available (J).a Second, particular attention has fulness in the care of patients. Some tests are essential been given to definition of the clinical conditions for for diagnosis, prognosis, or monitoring of disease; which the test is essential for diagnosis, those for many tests are useful but optional for routine investi- which the test is helpful in assessing or monitoring the gations; other tests are of interest only for research disease activity, and those conditions for which the purposes. In addition, a number of immunological test should be used only for clinical research purposes. tests are useless in some circumstances. The conclusions of this committee reflect the There is a consensus among immunologists that an present status of the art and do not preclude future effort should be made to reduce their share in the con- improvements. It was the feeling that the primary goal tinually increasing cost of medical laboratory investi- ofclinical immunology should be to help the patient in gations. This requires self-limitation in the routine the most cost-effective manner. QUANTIFICATION OF IMMUNOGLOBULINS The assessment of the three major immunoglobulin immunological methods is important in a limited classes in body fluids involves three laboratory tech- number of clinical conditions. This test is too often niques: serum electrophoresis, quantification of performed without good indication. major immunoglobulin classes, and immunoelectro- phoresis. The measurement of IgE requires more METHODOLOGICAL CONSIDERATIONS sensitive techniques (see pages 720-721). There is no clinical indication for the measurement of serum IgD. Quantification of the immunoglobulin classes by Many methods have been described for the quanti- tative assessment of immunoglobulins. Two of them * This Memorandum was prepared by the participants in a work- are currently of the most value and of comparable ing group organized jointly by the International Union of Immuno- logical Societies and the World Health Organization, in Geneva on accuracy: a) radial immunodiffusion (RID) and b) 18-20 May 1981. The names of the participants are listed on pages nephelometry. 727-728. Reprints should be requested from Chief, Immunology, World Health Organization, 1211 Geneva 27, Switzerland. A French a MACKAY, I.R. & RIrTS, R.E. WHO handbook of immuno- translation of this Memorandum will appear in a later issue of the logical techniques. Unpublished WHO document, WHO/IMM. Bulletin. TECH/79.1 (1979). 4107 717- 718 WHO MEMORANDUM When the patient load is relatively low, RID will Normal values probably remain the method ofchoice. However, with Concentrations of immunoglobulins in sera vary a high patient load and if a nephelometer is already with age, geographical environment, and sex. Each available, nephelometry is useful. laboratory should measure serum immunoglobulin concentrations on a matched control group. Radial immunodiffusion Radial immunodiffusion has a constant coefficient of variation which under optimal conditions may be less than 10%, except at extremely low concentra- CLINICAL INDICATIONS tions. The limit of accurate protein measurements, using low concentrations of antisera, is about 10 mg/l (10 Mg/ml). Techniques using limited diffusion are Serum more accurate than those with timed diffusion. With Quantification of serum immunoglobulins is re- normal sera, results can be obtained after 24 h of dif- garded as essential in suspected primary or secondary fusion, but more time may be required for the assess- immunodeficiency (ID), even when no abnormality is ment of very high or very low levels. seen in electrophoresis. Concentrations of immuno- Pitfalls. RID is sensitive to differences in diffusion globulins cannot be used, however, as the sole constants; special precautions should be taken to criterion for diagnosis of primary ID. Selective IgA ensure that immunoglobulins in the standard and test deficiency may occur without any evidence of associ- sera are not split or aggregated and are in the same ated disease, and IgA is undetectable in approximately form. For instance, reliable measurements of such 0.03-0.2% of the normal population. On the other proteins as IgM of low relative molecular mass and hand, failure to respond to one or more antigens can secretory IgA cannot be made unless a standard prep- sometimes be observed in patients with normal or high aration of these kinds of immunoglobulin is used. levels of all immunoglobulins. Thus, normal immuno- globulin concentrations do not exclude antibody deficiency. Monitoring of serum immunoglobulin Nephelometric techniques levels is essential in patients with severe forms of These techniques are increasingly used for quantify- hypogammaglobulinaemia who receive immuno- ing serum immunoglobulin levels. Both turbidimetric globulin substitution therapy. procedures and the detection of antigen-antibody Quantification of serum immunoglobulins is con- complexes by light scattering can be applied. The sidered helpful in distinguishing "benign" idiopathic advantages are that results can be obtained within a monoclonal gammapathies from paraproteinaemias very short time, they can be fully automated, and there caused by myeloma. In the latter case, the levels of are no problems with polymeric immunoglobulin. normal immunoglobulins are usually decreased, while they usually are unaltered in the "benign" form. In Pitfalls. Expensive instrumentation is required and this context, it should be stressed that monoclonal turbid serum samples may need to be clarified. immunoglobulins tend to give falsely high values in immunodiffusion assays. When large enough amounts of the monoclonal protein are present, it is Standards and antisera more accurate to measure the protein by the area Discrepancies in results have arisen from the use of under the spike on serum protein electrophoresis. different standards by different laboratories. WHO The value of quantifying serum immunoglobulins makes available International Reference Preparations for other clinical purposes has been established in only for the five classes of human serum immunoglobulin a few additional instances, such as the determination and it is recommended that working standards should of IgM levels in the cord blood of infants suspected of be related to these preparations. having congenital infections, and as an aid in the diag- Each antiserum, including those from commercial nosis of trypanosomiasis or tropical splenomegaly. sources, must be shown to be specific in the test in For research purposes, immunoglobulins may be which it is being used. Hybridoma-derived mono- quantified in diffuse hypergammaglobulinaemia and clonal antibodies may be useful in the future; how- in conditions such as some lymphoproliferative ever, many monoclonal antibodies do not precipitate diseases, liver cirrhosis, or systemic lupus erythema- antigen when used alone, and thus mixtures of such tosus. More promising might be immunoglobulin antibodies may be required. With these antibodies, it studies in the families of patients with immunodefi- may become easier to quantify subtypes and sub- ciency or homogeneous immunoglobulins, with the classes of the immunoglobulins. object of clarifying the role of genetic factors. DIAGNOSTIC PROCEDURES IN CLINICAL IMMUNOLOGY 719 Other bodyfluids ted CSF since concentration procedures will lead to the aggregation of immunoglobulins, especially IgG, Urine. Quantification of immunoglobulins in the and a falsely low value by RID. urine is possible but fraught with problems. For Quantification of immunoglobulins in CSF is of instance, immunoglobulin molecules in urine may be interest in diseases such as multiple sclerosis and sub- split or light-chains may exist in urine as monomers, acute sclerosing panencephalitis where the concentra- making standardization difficult. For the demonstra- tion of IgG relative to the
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