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Test characteristics: Difference between revisions
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== Biological variation == | == Biological variation == | ||
The human body is tightly regulated by homeostasis, but no compound in the blood stays at the exact same level over time | The human body is tightly regulated by homeostasis, but no compound in the blood stays at the exact same level over time, causing the concentration of compounds to fluctuate over time. The concentration of compounds in the blood change with age, time of day, food intake, any inflammation in the body, etc. This is called biological variation. | ||
Some compounds follow a predictable pattern, like circadian variation in cortisol or female sex hormones in the menstrual cycle. Other compounds fluctuate randomly around a homeostatic set point. | |||
For example, measuring HbA1c over time is important in the follow-up and management of diabetes mellitus. However, as with any biomarker, HbA1c has biological variation, which is approximately 3.2%, meaning that a 3.2% change in HbA1c over time may reflect a normal biological variation in the biomarker rather than an actual increase or decrease in long-term average blood glucose. | For example, measuring HbA1c over time is important in the follow-up and management of diabetes mellitus. However, as with any biomarker, HbA1c has biological variation, which is approximately 3.2%, meaning that a 3.2% change in HbA1c over time may reflect a normal biological variation in the biomarker rather than an actual increase or decrease in long-term average blood glucose. | ||
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# Those with measurements in the 5% range may have subclinical disease | # Those with measurements in the 5% range may have subclinical disease | ||
<noinclude>[[Category:Public Health]] | == Analytical sensitivity == | ||
Analytical sensitivity refers to the lowest detectable level of the particular analyte. For example, the lowest detectable level of TSH is 0,01 mIU/L. | |||
== Analytical specificity == | |||
Analytical specificity refers to the extent to which the test can identify only a specific substance, without interference from other substances. For example, the instrument which measures lactate cannot reliably distinguish between lactate and glycolic acid, a breakdown product of ethylene glycol, potentially giving falsely elevated levels in cases of ethylene glycol intake.<noinclude>[[Category:Public Health]] | |||
[[Category:Laboratory Medicine]] | [[Category:Laboratory Medicine]] | ||
</noinclude> | </noinclude> | ||