Which specimen is considered best for testing iron levels in the blood?

When assessing the best specimen for testing iron levels in the blood, the most appropriate choice is the serum collected in a plain tube. This is because serum is typically what is analyzed in laboratory tests for iron levels.

In serum testing, the iron is measured in the liquid portion of the blood after the cells and clotting factors have been removed. This type of specimen provides a clear measurement of the circulating iron in the bloodstream, making it the gold standard for such testing.

While blood samples collected in tubes containing EDTA are commonly used for other tests, such as complete blood counts, they can interfere with certain tests due to the binding properties of EDTA with metals, which may skew the results for iron levels.

Capillary blood from a finger prick can be less reliable for measuring iron levels, as this method may not provide an adequate sample size and the composition of the blood may vary compared to venous blood. Therefore, serum collected in a plain tube is the preferred choice for accurate iron testing.