Why have you changed how you test oestradiol?
Our partner laboratories have advised us that the oestradiol test is more accurate when performed on a red-top finger-prick tube. The yellow top finger-prick tube may return lower than expected results. Therefore, we have switched all our finger-prick tests containing oestradiol to red-top tube kits.
What causes the lower than expected result?
The gel at the bottom of the yellow top tube is designed to make the blood clot and collect the blood cells. This is to help the laboratory process the sample efficiently. It is thought that the gel absorbs oestradiol from the serum (the liquid in the tube), lowering its concentration.
Why are finger-prick samples affected but not venous?
Our understanding is that in a finger-prick collection tube, the surface area of the gel is much greater relative to the volume of serum so the oestradiol is absorbed at a faster rate. In a venous tube, the volume of serum is much greater relative to the surface area of the gel so the oestradiol is absorbed at a much slower rate.
Are you sure venous samples are not affected?
Our new laboratory has tested yellow top venous tubes and found that results are not significantly affected.
I've tested oestradiol with you in the past. What should I do?
We would like to reassure you that there is unlikely to be a significant difference in how your test was interpreted.