what is diffence in standard deviation & coefficient of variation in clinical pathology laboratory?

Question

clinical pathology results generated on automated instruments

Answer 1

Clinical pathology laboratories must monitor the accuracy and precision of their lab tests.

A "normal" laboratory result will be the test value that is inside two standard deviations of the laboratory's mean value for that test.

In addition to determining whether a given lab result is within normal range, i.e. whether or not it fits within plus or minus two standard deviations, it is important to determine if the mean and standard deviations for that test stays stable or drifts up or down over time.

Laboratory accrediting agencies provide calibrated check samples that have precisely known test values.

Without regularly using check samples along with patient samples a laboratory might find it difficult to determine when or if its normal values have changed because an instrument has gotten out of calibration or if the patient population has somehow changed.

The coefficient of Variation [CV] for a given lab test equals the standard deviation for that test divided by the mean for that test. In general this should be a small number less than one.

If the CV gets bigger it means that the test results include more extremely abnormal results or contain errors due to instrument miscalibration or laboratory technician errors.

Gradual Drift upward of CV usually signals the need to recalibrate instruments or retrain personnel.