Any reason an iron test should be done first thing in the morning?

[Boldgirl45]

Thanks!

[Boldgirl45]

Just to say for various reasons I have to have it in the evening today! I can fast if that's the issue?

[ChrisColumbus]

To get the most accurate results in an iron level blood test it is (NHS) best practice to observe a fasting time - including only water as fluid intake - of 12 hours. It is much easier for most of us to do this overnight before a morning test! However, if needs must...!

If you normally take iron supplements you should also have stopped these 48 hours before the test.

[Boldgirl45 in reply to ChrisColumbus]

Thanks very much !

[SueJohnson]

Yes there is a reason. Your ferritin is highest in the morning. If you take it later it will give a lower number which might make you think you need to take iron when you don't or if it is low enough your doctor might think you are anemic when you aren't. That is when all the reference values are based on. If you can't take it in the morning I would postpone it until you can. By the way be sure to stop taking any iron supplements including in a multivitamin 48 hours before the test, and avoid a heavy meat meal the night before. And you only need to fast after midnight, not for 12 hours.

[ChrisColumbus in reply to SueJohnson]

Hi Sue: in the NHS while fasting for 8-10 hours is recommended for some blood tests, including for blood glucose, 12 hours is recommended for iron. Nuffield Health (private provider) says 8-12 hours for iron.

I now see that Mayo on the other hand says "If your blood sample is being tested only for ferritin, you can eat and drink normally before the test. If your blood sample will be used for other tests, you might need to fast for a time before the test."

mayoclinic.org/tests-proced...

[SueJohnson in reply to ChrisColumbus]

It says "Determine the patient’s iron status (early morning, fasting iron panel: serum ferritin, iron, total iron-binding capacity, and percentage transferrin saturation)" I don't see anywhere and I searched for every mention of ferritin where it says "If your blood sample is being tested only for ferritin, you can eat and drink normally before the test," I searched for "being tested only" and found nothing.

I saw the NHS but testing for iron is not the same as as a full panel iron test. "an iron blood test (used to diagnose conditions such as iron deficiency anaemia) – you may be asked to fast for 12 hours before the test."

I stand by my fast after midnight. But it can't hurt to fast longer, and if one has their test at 9 am it is not likely one will be eating anything after 9 pm.

[ChrisColumbus in reply to SueJohnson]

On the matter of ferritin levels during the day, while I've also seen this given as a reason for testing in the morning, the only analysis I've found today is a Lab Me report from 2021 which states:

"Although statistically significant differences among mean values for the collection times were observed for iron, iron-binding capacity, and (log) ferritin, no consistent diurnal variation was seen. Morning iron levels were higher than afternoon levels for only half of the subjects. Between-day variation for all 4 analytes was similar to within-day variation.

We conclude that the practice of restricting iron specimen collections to a specific time of day does not improve the reliability of the test"

While Lab Me haven't obviously credited the source for this research, they seem to have lifted it word for word from here:

pubmed.ncbi.nlm.nih.gov/120...

I note this dates back to 2002: perhaps more recent research contradicts this?

[Joolsg]

Professor Walker gave a speech on iron at the RLSUK AGM.He said that iron supplements should be taken in the morning, not the evening, because Hepcidin is lowest in the morning. Hepcidin blocks iron absorption.

So, I assume it's for a similar reason. Hepcidin is lowest in the morning, so your normal iron levels will show up better then.

There are probably additional reasons.

[Boldgirl45]

thanks everyone!

[WideBody]

from my favorite paper.

“Because (1) of the distinct circadian changes in serum iron (highest in the morning and lowest in the evening) [106], (2) of increases in serum iron immediately after food intake, and (3) of serum iron's importance as an independent determinant of iron status (plus part of the calculation of percent iron saturation), serum tests of iron should be obtained in the morning after an overnight fast. Where possible, the last meal prior to the fasting period should have a limited amount of meat, particularly red meat.”

Serum iron is highest in the morning, Ferritin is lowest in the morning.

To many experts Transferin Saturation Percentage is more important than Ferritin. TSP is a calculated using serum iron.

As someone who has been burned in the past, doing it in the morning is best.