Have UK ref ranges for ferritin changed?

[Sleepybunny]

Hi,

I'm sure I read on the forum recently that UK ref ranges for ferritin have changed.

Does anyone know if this is true?

I can't find the post where it was mentioned so please post a link if anyone finds it or to other UK documents/guidance.

Apologies if this is a false memory.

I've found it...

cks.nice.org.uk/topics/anae...

Above link says "In all people, a serum ferritin level of less than 30 micrograms/L confirms the diagnosis of iron deficiency."

[helvella]

I think you are referring to this:

Serum ferritin level is the biochemical test, which most reliably correlates with relative total body iron stores. In all people, a serum ferritin level of less than 30 micrograms/L confirms the diagnosis of iron deficiency. However:

Ferritin levels are difficult to interpret if infection or inflammation is present, as levels can be high even in the presence of iron deficiency.

Ferritin levels may be less reliable in pregnancy.

cks.nice.org.uk/topics/anae...

However, whilst this might imply that laboratories should re-consider their reference intervals (ranges), I am not aware of any mechanism for the NICE guidelines actually getting translated into such changes.

There is little clear about the basis for existing (pre-guideline) ferritin reference intervals. They appear to vary far too much to make sense.

Adding:

NICE Clinical Knowledge Summaries do not have the same status as full NICE guidelines.

[Nackapan in reply to helvella]

It wad in an April NICE review.I couldn't find the post or who replied.

[Nackapan]

Yes a reply to me and I checked. Changed in April 2021. Will try snd find the post

[Narwhal10]

Thanks Sleepybunny,

[FlipperTD]

Scientist's, not medic's answer. Treat with caution, but it's from personal, practical experience of running an assay service.

Ferritin is assayed using an immunoassay. This requires an antibody directed at human ferritin. Different equipment manufacturers have their own systems in place and usetheir own anibodies. In consequence, the sensitivity of the tests may vary between manufacturers. One may have a wider range that can be considered as 'normal' than others. When assay methods and equipment are changed it's vital to compare the sensitivity of the 'old' versus 'new' methods. There are numerous ways of doing this, and in general, the easier ones are more suspect, because it could be that the 'old' one had been 'fiddled' [sorry, colleagues] to take account of a previous change. This could have happened several times over a period of years. All UK NHS laboratories participate in at least one external quality assurance scheme, but this doesn't mean that results from all methods are comparable. It simply allows comparison of results from one manufacturer's method with others using the same method.

Many analytes [for example Haemoglobin] can be compared with high confidence between manufacturers, laboratories and methods, but immunoassays are much more of a challenge.

[helvella in reply to FlipperTD]

Must say, even after what you have said, I find the extreme variation in ranges disconcerting.

I just gathered a number of ranges that have recently been posted, bunged then into a spreadsheet and pasted here. (I think all are for females.)

How on earth should we take statement's such as the NICE CKS one about a minimum of 30? Or a widespread "Ferritin should be about halfway in range - 70 to 80"? If the lower limit is 33, are they saying it should drop to 30?

We have also seen numerous discussions about what GPs do if you are over-range. Which seems to be ignore it until it is much higher! It sometimes looks as if some labs have raised the top of reference interval on the basis that no action will be taken between, say, 150 and 300.

And could 10 on one lab's test be "the same" as 34 on another (bottom of reference intervals - plus one)?

[FlipperTD in reply to helvella]

Hi. Thanks for your prompt response, and you're right to be concerned and possibly confused.

Without knowing the methods involved, it's difficult to comment, but it's probably safe to say that one lab's '10' is very unlikely to be the same as another's '34', given the 3.4x difference. It's (statistically) confusing, at best.

The distribution of ferritin results within a population isn't Gaussian, and that adds to the complications.

It is probably fairly safe to assume that if your test is being done at the same laboratory, then the method is unlikely to change too often, and as a consequence the 'reference range' should be consistent. However, that doesn't get over the problem of 'where did the reference range come from in the first place?' Deriving reference ranges is a challenge, at best. Relying on a large supply of 'normal' samples (starting with defining what 'normal' actually means) is one problem. Then taking the cost, time and reagents to assay those samples. Then deciding what statistical methods to use to analyse the data. As a consequence, if the method has been changed, it's likely that a fix of testing samples in duplicate by the two methods, and then simply plotting 'x vs y' and deriving the slope and intercept, and using those to fudge the upper and lower limits. So any inherent problems remain, but at least the ranges are (sort of) consistent. I don't suggest this is acceptable, but it probably fairly closely describes what has gone on in the past.

(I'm in great danger of getting off the subject!)

[nellie237]

NICE Anaemia go to

'How up to date is this topic/Changes"

April 2021 — minor update. Diagnostic level of ferritin level was changed from 15 micrograms/L to 30 micrograms/L

You can't take this on its own. Its a follow on from 'Investigations'

"If results of the FBC show a low haemoglobin and low mean cell volume (MCV) check the ferritin level — check the ferritin level in all people with an MCV less than 95 femtolitres."

ie If haemoglobin and MCV are low, then ferritin<30 confirms anaemia.