Background: Among other methods, trichloroacetic acid precipitation is used to quantify total protein in cerebrospinal fluid (CSF).
Methods: We analyzed the influence of hemoglobin on total protein concentration assayed by the trichloroacetic acid method and compared the results to the benzethonium chloride method.
Results: Four CSF samples were spiked with different amounts of hemoglobin, leading to overestimation of protein concentration when assayed by the trichloroacetic acid method. Using the benzethonium chloride method, measurement of protein concentration was minimally disturbed. In addition, albumin and total protein concentrations were measured in 135 clinical samples. The total protein/albumin ratio remained constant when protein was measured with the benzethonium chloride method, while ratios increased when protein was assayed by the trichloroacetic acid method.
Conclusions: Strong interference by hemoglobin leads to overestimation of the total protein concentration in CSF when assayed by the trichloroacetic acid method and may lead to false conclusions when evaluating the blood-brain barrier.