Clinical Laboratory - Fundamentals

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Critical Values

Critical Values; Turnaround time; and Stat vs. Routine Test Priorities

The "turnaround time" is defined as the reporting interval. The beginning time for this interval may be defined for various purposes as the time the test was ordered, the time the specimen was obtained, the time the specimen reached the laboratory, or the time the test was completed. For most routine testing, this is defined as the time from receipt of the specimen in the laboratory to the time the result is reported. Turnaround times are set by the need for timeliness of reporting for clinical decision-making.

A "critical value" is a test result that conveys life or death information and is defined for "out of range" test results that must be acted upon as soon as possible. For example, most laboratories define a serum glucose value below 40 mg/dL as a critical value, because that degree of hypoglycemia carries a high risk for morbidity and mortality. A critical value has life-threatening, time-dependent implications and must be directly reported to the health care provider for immediate action.

A "stat" test is defined as a quick turnaround time, generally an hour or less from specimen receipt until test result reporting. Such stat tests are usually ordered when the result is needed quickly for a decision regarding patient management. Such tests must be performed ahead of others in the queue. Many tests ordered from an emergency department, such as electrolytes, are handled as "stat" tests.

"Routine" test turnaround applies to specimens for patients without immediate need for results. This may be determined by the frequency the test is run in the laboratory: several times per day, once per day, once per week, etc. Tests results are availble within hours to days. For more esoteric tests sent out to a reference lab, results could take at least a week.

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