individual, when taking all significant factors of that individual into account - a task that may be hard to achieve by studies, but long clinical experience by a physician may make this method preferable to using reference ranges. one-sided cut-off values in many cases, only one side of the range is usually of interest, such as with markers of pathology including cancer antigen 19-9, where it is generally without any clinical significance to have a value below what is usual in the population. therefore, such targets are often given with only one limit of the reference range given, and, strictly, such values are rather cut-off values or threshold values. they may represent both standard ranges and optimal health ranges. also, they may represent an appropriate value to distinguish healthy person from a specific disease, although this gives additional variability by different diseases being distinguished. for example, for nt-probnp, a lower cut-off value is used in distinguishing healthy babies from those with acyanotic heart disease, compared to the cut-off value used in distinguishing healthy babies from those with congenital nonspherocytic anemia. general drawbacks for standard as well as optimal health ranges, and cut-offs, sources of inaccuracy and imprecision include: instruments and lab techniques used, or how the measurements are interpreted by observers. these may apply both to the instruments etc. used to establish the reference ranges and the instruments, etc. used to acquire the value for the individual to whom these ranges is applied. to compensate, individual laboratories should have their own lab ranges to account for the instruments used in the laboratory. determinants such as age, diet, etc. that are not compensated for. optimally, there should be reference ranges from a reference group that is as similar as possible to each individual they are applied to, but it's practically impossible to compensate for every single determinant, often not even when the reference ranges are established from multiple measurements of the same individual they are applied to, because of test-retest variability. also, reference ranges tend to give the impression of definite thresholds that clearly separate "good" or "bad" values, while in reality there are generally continuously increasing risks with increased distance from usual or optimal values. with this and uncompensated factors in mind, the ideal interpretation method of a test result would rather consist of a comparison of what would be expected or optimal in the individual when taking all factors and conditions of that individual into account, rather than strictly classifying the values as "good" or "bad" by using reference ranges from other people. in a recent paper, rappoport et al. described a novel way to redefine reference range from an electronic health record system. in such a system, a higher population resolution can be achieved (e.g., age, sex, race and ethnicity-specific). examples reference ranges for blood tests reference ranges for urine tests