Increased lipid concentration is associated with increased hemolysis.

To the Editor: The relationship between serum lip-ids and erythrocyte membrane fra-gility is complex (1). As seen in routine laboratory practice, samples with hypertriglyceridemia or mixed hypercholesterolemia and hypertri-glyceridemia can present as visibly turbid (" milkshake " appearance), but more often they present as " strawberry milkshake " because of increased hemolysis. The amount of hemolysis appears to increase as the lipid concentration increases, although the extent of this effect is not well characterized. We investigated whether a relationship exists between an increase in total lipid concentration (cholesterol plus triglycerides) and hemoly-sis in actual patient samples. To determine this relationship, we assessed all samples collected for lipid analysis during 2003 and 2004. Samples from the hospital emergency department were excluded because such samples have a high incidence of being grossly hemolyzed (2). As a routine procedure, hyperlip-idemic samples with a milkshake appearance and optical turbidity (i.e., it was not possible to see through the sample) were analyzed for cholesterol , triglycerides, and amount of hemolysis [hemolytic index (HI)] on the Hitachi Modular System with Roche reagents (Roche Diagnostics). The HI was determined by measuring the difference between the absor-bance of the sample diluted in iso-tonic saline at 570 and 600 nm. The hemolysis absorbance value was converted to mg/dL by a multiplication factor. All optically turbid samples were ultracentrifuged on an Air-fuge (Beckman Airfuge, Beckman Coulter Diagnostics) for 15 min at 20 psi air pressure and 107 000g (90 000 rpm). The samples were divided into 6 groups based on increasing lipid concentrations (tryglycerides and cholesterol; Table 1). The mean HI for each group was then determined. For lipemic samples containing tri-glyceride concentrations Ͼ15 mmol/L, HI was evaluated after ul-tracentrifugation. Lipemia did not affect the HI when the triglyceride concentration was Ͻ15 mmol/L, but when the triglyceride concentration was Ͼ15 mmol/L, we observed an increase in spectrophotometric arti-facts (data not shown). We used the association between hyperlipidemia and hemolysis [ln(HI)] to normalize results for all samples. Multiple linear regression analysis of ln(HI) values indicated that both cholesterol (P Ͻ0.001) and triglycerides (P Ͻ0.001) were linearly related to the HI. The data at higher lipid concentrations (Table 1) suggest that the triglyceride concentration has a greater influence on the HI than the cholesterol concentration. Interestingly, for paired groups with similar triglyceride concentrations, those with a higher cholesterol concentration had a slightly lower HI. A detailed discussion as to possible mechanisms for …