The various techniques just mentioned are based on different properties of protein molecules (e.g., chemical, dye-binding, electrical charge, antibody binding sites). Therefore, the different techniques may not produce identical values for all protein fractions or for individual proteins. Added to this are alterations in proteins from disease or genetic abnormalities, different interfering substances or medications, and technical problems unique or important for each technique or method. For example, the serum albumin value by electrophoresis may be about 0.5 gm/100 ml (5 g/L) less than the value determined by the usual chemical method. This is fortunately not often very important as long as the same laboratory performs the tests on the same patient and provides its own reference range. The differences in technique and methodology are magnified when the quantity of protein being assayed is small, such as in urine or spinal fluid. Since even modifications of the same method can produce slightly but significantly different results, reference values should be obtained by the individual laboratory for its own particular procedure.