Effects of sodium azide on the quantitation of the chemical constituents of serum. Inhibition of bilirubin and cholesterol.

Azide salts frequently are added as a preservative to biologic fluids and reagents, or are introduced into serum through accidental exposure, intoxication, or pharmaceuticals. Sodium azide can interfere with the quantitation of biochemical constituents in serum. Serum pools containing 0.2-9.0 mg/dl (3.42-153.9 mumol/l) total bilirubin, 0.2-5.0 mg/dl (3.42-94.1 mumol/l) direct bilirubin, and 175-313 mg/dl (4.55-8.14 mmol/l) cholesterol were analyzed using the SMA 12/60. Sodium azide was added in concentrations of 0.1-1.0% (13.6-136 mmol/l). Sodium azide in concentrations of 0.1% (13.6 mmol/l) or more reduced total and direct bilirubin values 60-100%. At concentrations above 0.5% (68 mmol/l), no bilirubin, or only a very small quantity, was measured. Sodium azide at concentrations above 0.05% (6.8 mmol/l) exerted a significant decreasing effect on serum cholesterol values. At 0.1% (13.6 mmol/l) or more, reductions in cholesterol values ranging from 30 to 85% were observed. These studies showed that sodium azide (0.1%, 13.6 mmol/l, or more) in the serum can result in falsely low bilirubin or cholesterol values.