Sulfate Information and Courses from MediaLab, Inc.

False negative bilirubin dipstick results are often due to testing a specimen that is not fresh. Bilirubin breaks down when exposed to light. Indoxyl sulfate (Indican) can produce a yellow orange-to-red color response which may interfere with the interpretation of a positive or negative reaction. Positive nitrites due to a urinary tract infection may also cause a false negative result.

There are several acids which can be used to precipitate proteins - sulfosalicylic, trichloroacetic, nitric, and acetic acids. Sulfosalicylic acid (SSA) is the most frequently used acid test because it does not require the use of heat. Exton’s reagent is 5% sulfosalicylic acid in a solution of sodium sulfate. Exton (1925) found that adding sodium sulfate to the SSA causes a more uniform precipitate to be formed. To perform the SSA procedure mix equal parts of patient urine and the reagent. Rate the amount of turbidity according to the following scale:

Denaturing chemicals can be added to the acrylamides during formation of polyacrylamide gels. These additives keep the solutes or molecules in a denatured state during separation. Urea denatures double-stranded DNA to single-stranded DNA. A detergent, sodium dodecyl sulfate (SDS), denatures proteins. Adding SDS with heat denatures proteins to small, similar shaped particles and coats each so that protein structures are not reformed. SDS is usually added to the gel and the protein sample. Then the mixture of protein coated fragments moves through polyacrylamide gel pores with speed similar to a mixture of DNA fragments.

In the clinical laboratory, we routinely measure the cholesterol content of high-density lipoprotein and low-density lipoprotein particles and not the apolipoproteins on the particles or the number of particles. Proprietary detergents and reagents are used in assays for HDL-C and LDL-C to separate lipoproteins, allowing the cholesterol content of specific lipoproteins to be measured. For example, HDL-C is commonly measured using a solution of dextran sulfate and magnesium to selectively precipitate HDL from the other lipoproteins present in the sample. Once isolated, the HDL particles are 'dissolved' and the amount of cholesterol in them is determined photometrically using a color-producing enzyme reaction. LDL-C can be measured directly or can be estimated using the HDL-C, triglycerides and total cholesterol (TC) values. The Friedewald formula is often used to calculate LDL: LDL-C = TC - (HDL-C)+(Triglycerides/5). The important point to consider here is that traditional LDL-C and HDL-C measurements only tell us how much cholesterol is associated with each lipoprotein particle class. We are now learning that the number and size of the particles are important as well. The number of LDL particles appears to be more strongly predictive of cardiovascular disease than the LDL-C content, and small dense LDL are known to be more atherogenic than larger, less dense LDL particles.