A new approach to the costing of clinical laboratory tests.

A method of costing clinical laboratory tests is described which avoids the assumptions and omissions of previous methods and overcome the basic theoretical difficulty of allocating indirect (overhead) costs, which form the major component. The method develops the concept of a "cost per request' to cover the indirect cost, which reflect the cost of providing laboratory facilities, and a 'cost per test' to cover the direct analytical costs of the individual tests done. The direct cost per test was found to vary with the workload, which makes it difficult to predict the effect of changes in demand on expenditure. The Canadian Schedule of Unit Values was found to be an unreliable basis for calculating direct labour costs. Examples are given of the direct and indirect costs of consumables, labour, and capital, and their contribution to the total cost of clinical chemistry tests done either during or outside normal working hours. The total annual cost for each analyte may be a more useful indicator of expenditure than the cost per test.

A reassessment of 8-anilino-1-naphthalene sulphonic acid as a thyroxine binding inhibitor in the radioimmunoassay of thyroxine.

The effectiveness of 8-anilino-1-naphthalene sulphonic acid (ANS) in the radioimmunoassay (RIA) of thyroxine (T4) as an inhibitor of the binding of T4 to serum T4-binding proteins is assessed. The optimum ANS concentration is dependent upon the antiserum and the method used for separating free and bound T4. If T4 binding to serum proteins is not completely inhibited, resin separation methods may yield low values, while polyethylene glycol and double-antibody methods may produce high values for T4 concentration. Even with optimum ANS concentration gross errors in measurement of T4 may occur in patients with high thyroxine-binding globulin (TBG) concentrations.