I suspect few, if any, of us have ever really thought about iron tests varying by time of day. However much we understand with regard to thyroid, somehow I think most of us imagine iron as being more "bucket chemistry".
But this paper might force us to re-assess!
Influences of sleep and the circadian rhythm on iron-status indices
Peter Ridefelt 1 , Anders Larsson, Javaid-ur Rehman, John Axelsson
Objectives: The aim was to study the influence of sampling time, food intake and sleep on tests used to screen for and monitor conditions of iron deficiency and overload.
Design and methods: The 24 h variations of iron, transferrin, transferrin saturation (TS) and ferritin were studied in seven healthy individuals during standardised food intake, and during night or day sleep.
Results: Iron and TS showed clear diurnal variations, with peaks at 12.6 h and 12.8 h respectively, during night sleep, and at 19.7 h and 19.3 h, respectively, during day sleep. Ferritin did not demonstrate any circadian variation. Transferrin and ferritin were unaffected by sleep-condition. Meals did not have any effect except a slight decline of transferrin.
Conclusions: Time of day and sleeping patterns had great influence on iron and TS, whereas no or only minor effects are seen on the concentration of ferritin and transferrin. Meals have limited effects.
The abstract and a weird collections of snippets from the full paper available here - but full paper, depressingly, is behind a paywall.
I think we have moved from time of blood draw being important only for a few known things - cortisol being an obvious example - to a situation in which the documentation of every analyte should say whether it is affected by time, and a brief note of explanation.
I must be being really stupid but what do the timings actually mean?
Iron and TS showed clear diurnal variations, with peaks at 12.6 h and 12.8 h respectively, during night sleep, and at 19.7 h and 19.3 h, respectively, during day sleep.
With 60 minutes in the hour 12.6 h comes out as 12.36am and 12.8 h comes out as 12.48am
19.7 h comes out as 7.42pm and 19.3 h comes out as 7.18pm.
They use am and pm in the small amount of the paper they actually make publicly available.
So why have they given timings that are so weird when they could have just used normal clock time? Is it the number of hours since sleep onset?
The aim of this paper was to provide data for clinical laboratories on how iron, transferrin, TS and ferritin should be sampled, as well as information on factors that may affect the interpretation. This was done by studying the 24 h variation in a group of healthy individuals during standardised conditions of food intake, and with normal night sleep as well as during acutely displaced sleep.
When looking at 24 hour variation were they talking about midnight to midnight? Noon to noon? Normal clock time?
They appear to have made the little bit of their paper that they published as opaque as possible.
I've been sitting on the paper for a while deciding whether to post. Eventually concluded that simply knowing there are issues is important enough - despite lack of sufficient detail.
And please can we get away from am/pm and stick with 24-hour format? I always have, and always will, find it difficult to get my head round the logic of whether 12:00 am is midday or midnight! Which is why no military operation ever starts at 12:00!
(Do what you like for yourself and at home. But when writing things up for international consumption, let's just keep to one simple standard that doesn't need to be translated!)
And please can we get away from am/pm and stick with 24-hour format?
Yes, I would normally agree. But - in this particular instance - if I had used that it would have made the references to 12.6 h or 19.7 h even more confusing!
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Transferrin saturation iron results query please?
Iron Blood Test out of range - advice please!
