The delta check value is the measured difference between the results of consecutive laboratory tests of the same individual. When this value is higher than expected, such a result may indicate a problem in testing with the previous or current sample and should be investigated in a timely manner, before the results are published. The classic formula for calculating delta check is subtracting the current parameter value from the previous parameter value for the same individual. In addition to this, other approaches to calculating the delta check have been developed. The delta check percentage is calculated by multiplying the difference between the current value of the parameter and the previous value by 100 and then dividing by the current value of the parameter or calculating the quotient of the current value of the parameter and the previous value. In the case of calculating the difference between the current value and the previous value of the parameter, it must be within limits called delta check limits. In calculating these limits, we must take into account: intraindividual biological variations for the parameter being examined (coefficient of variation CVi - the ratio of standard deviation to the mean value); analytical variation (SD - standard deviation, which can be easily calculated using control values, and represents the average deviation from the average); preanalytic variations (CVpre-analytic); improvement or deterioration of the individual's health and errors in the pre-analytical, analytical or post-analytical stages of work. The criteria for choosing an analyte for delta check have several limitations. Analytes that have a low coefficient of intra-individual variation are most often used, which prevents the possibility of a false alarm, but reduces the possibility of detecting an error. Another limitation is the interval in which the delta check is performed, because it is short, so only tests that are repeated frequently in short time intervals are useful. The use of the delta check method is a simple method of comparing results that indicates the existence of certain significant changes in the metabolic status of an individual.
