A 49-year-old man had experienced epistaxis, dyspnea, and weakness for several months. His sclerae were icteric and pale, and he had retinal hemorrhages as well as marked tortuosity and dilatation of the retinal veins. The liver and spleen were not palpable and he had no peripheral lymphadenopathy.

A peripheral smear showed marked erythrocyte rouleaux and plasmacytoid lymphocytes. Serum protein electrophoresis showed a striking spike Figure 1, and immunofixation electrophoresis showed a monoclonal IgM- . His bone marrow was replaced with mature and plasmacytoid lymphocytes. Serum viscosity was 8.3 (normal, <2.0). The Sia test result was strongly positive and the precipitate plummeted to the bottom of the tube; this finding was described by Waldenstrom [1] as typical of an IgM euglobulin. Electrophoresis of the water-diluted serum showed that the paraprotein was missing because the euglobulin had precipitated (Figure 1). Electrophoresis of the serum euglobulin precipitate showed that it was the monoclonal IgM (Figure 1).

View larger version (15K): [in this window] [in a new window]   Figure 1. Electrophoretic patterns of proteins in whole serum, supernatant of water-precipitated serum, and euglobulin precipitate at a dilution of 1:5.0 with distilled water.

Using the Miles-Technicon Dax 48 (Miles, Inc., West Haven, Connecticut), the chemistry laboratory reported his total serum protein concentration as 1.2, 1.7, and 0.6 g/dL, respectively, on the first 3 days after admission, whereas we obtained a refractometric estimate of 11.3 g/dL. The manufacturer recommended distilled water as the blank reagent to determine the total serum protein concentration. When the patient's serum was added to the water blank reagent, a heavy white precipitate formed, causing most of the total protein to be obscured. After we brought this problem to the attention of the manufacturer, they changed their recommendation to using 0.9% saline as the blank reagent for the total protein concentration.

However, even after we made that change, the Dax 48 showed a total protein concentration of 5.2 g/dL, whereas the refractometric estimate was 11.1 g/dL. This continuing problem was caused by the initial dilution of all serum specimens to 1:2.5 with distilled water. If the total protein exceeds 10 g/dL (or if the concentration of another analyte is abnormally high), then, according to the manufacturer, the serum must be further diluted to 1:5.0 with distilled water. At this dilution rate, most of the euglobulin precipitated (Figure 1). Therefore, the Miles-Technicon Dax 48 provides a falsely low estimate of serum total protein concentration if the specimen has a high concentration of protein, some of which is a water-insoluble euglobulin.