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Aims: To determine the value of the red cell distribution width (RDW) and erythrocyte zinc protoporphyrin (ZPP) concentration in discriminating between iron deficiency, and beta and alpha thalassaemia in a mixed urban Asian population., Methods: The RDW and ZPP concentrations were measured in 1412 subjects attending for outpatient phlebotomy, with classification into diagnostic groups on the basis of haemoglobin, mean cell haemoglobin, ferritin, HbA2 and haemoglobin electrophoresis., Results: Non-parametric 95% reference ranges for RDW were 11.7-15.7% and for ZPP 38-104 mumol/mol haem. Both RDW and zinc protoporphyrin rose with increasing severity of iron deficiency, but were also raised in significant numbers of subjects with beta and probable alpha thalassaemia., Conclusions: Measurements of RDW and ZPP do not differentiate between alpha or beta thalassaemia trait and moderate degrees of iron deficiency (hypochromasia without anaemia). ZPP is a more accurate indicator of iron deficiency than RDW and concentrations above 150 mumol/mol haem strongly suggest iron deficiency, usually with anaemia, rather than thalassaemia.

An immunoturbidimetric assay for the assessment of free kappa and lambda light chains of immunoglobulins was developed using a commercial polyclonal antiserum with reactivity towards epitopes on the light chains, which are not expressed when they are bound to heavy chains. The assay, on a centrifugal analyser, is simple and rapid. The limit of detection is 5 mg/l of free light chain, with an assay range of 5-120 mg/l, intrabatch precisions from 1.5-6.4%, and interbatch precisions from 6.5-8.9%. The assay was only slightly less sensitive than colloidal gold staining of cellulose acetate electrophoreses for the detection of Bence-Jones protein in urine. For the serial monitoring of response to chemotherapy in patients with myeloma, the assay correlated well with serum paraprotein estimates obtained by densitometric scanning of Ponceau stained cellulose acetate electrophoreses, but not with serum beta-2 microglobulin measurements, even after correction for the effects of creatinine. These assays may prove to be of use for the monitoring of tumour response in the treatment of Bence-Jones myeloma.