Assessment of a biuret method without concentration step for total protein determination in cerebrospinal fluid.

E xamination of cerebrospinal fluid (CSF) total protein is used chiefly to detect increased permeabili ty of the blood-brain barrier to plasma proteins or increased intrathecal secretion of immunoglobulins (1). A rapid and quite precise method is required. The biuret method is considered as a potential reference method for total protein determination in biological fluids (2-4). It has been modified to obtain sufficient sensitivity in CSF (concentration step with protein precipitation by trichloracetic acid, rate reaction, reverse reaction using bathocuproine, etc.). Unfortunately, most of these modifications decrease the practicability of this simple method and a require large volume of CSF (2,3,5). Several other techniques are available, including turbidimetry, dye-binding, and colorimetry (2-6). Each of these suffers from some problem, i.e., different sensitivity between albumin and globulins (2-4, 6), carry-over in nondisposable cuvettes in the analyzers and contamination of other reagents (4), need of a centrifugation step (4) or limited linearity (6). The aim of the s tudy was to assess the capacity of a one-step biuret method to measure total protein in CSF and to compare it with a convenient benzethonium chloride turbidimetry technique. Benzethonium chloride