...continued:
Ferritin is often the first thing in blood to react to iron deficiency (ID). It's also the most reliable value to test, even though it has some issues too. However, if serum (or plasma) ferritin is low, the result is always reliable. If it seems high, that's a different story. One thing that can cause a falsely high ferritin is a simple thing called inflammation. It can be an active one or a silent one. So ferritin should always be measured with crp or sed-rate, but even if those are ok, the "good" level of ferritin may be a lie.
Hemoglobin (Hg) may be falsely high for various reasons: Asthma, for one, because oxygen deprivation causes Hg to rise falsely. Also if you're dehydrated, Hg may seem a lot of higher than it actually is. And then, surprice - ID! That's because ID causes oxygen deprivation to the body, so the Hg may actually rise before starting to plummet because of full blown anemia.
Symptoms from low ferritin may be various, difficult and debilitating: Fatique, headaches, restless legs, tinnitus, skin problems, stomach problems, heart problems, muscle problems, pale skin and black under eyes...... the list is endless. And actually, ID without anemia is VERY often confused with hypothyroid issues, especially the sub-clinical ones. So before starting trial medication for hypothyroid, the pati ents ferritin levels should always be taken care of first.
Also, an important note: When finding ID, the reason should always be determined. Without finding out (and treating!) the root cause, pumping iron in the system is like pouring water in a bucket with holes in it. That's just stupid. Plus, sometimes the causes may be malignant.
With Sjögrens patients, the risk for ID (and vitamin B deficiency, too) is clearly elevated. That's because the nutrition absorption is compromised for various reasons.
What then is a good level of ferritin? WHO states that values under 12 means no iron in the system at all. Zero. But that's rather low, too, and depending on the source, values under 20 or 30 are considered serious ID and anything under 40 is ID. For adult women I've generally read that 100 is good, but depending on the person, some may need even higher values.
With restless legs some sources recommend ferritin at least 45 (which is LOW imho), others 70 or more.
With rheumatic diseases or chronic illnesses the level should be at least 100, considering the possibility of inflammation causing false readings.
Correcting low ferritin helps the thyroid function better, because iron is needed in the T4 -> T3 conversion process. So minor thyroid problems MAY be corrected with iron only. When looking into iron levels, also active B12 and vitamin D should be checked and corrected into proper level, because the balance is important. And those two vitamins are so very important for people in so many ways.
As an end-note (although I drafetd this text rather quickly and put it in short and I'm sure I'll soon remember loads of things I should've included in it), taking iron just by yourself can be dangerous, even lethal. So it's important to find a good doctor who knows what he's doing and why, and keeps monitoring your progress. Correcting very low ferritin levels can sometimes take a very long time, even two years. It cannot be achieved by correcting your diet - there's no way you can get so much excess iron from food. You need iron pills, or, if you can't use those or they don't help, then infusions.
The professionals on this forum, Irish, Linda and others, please correct if there are any mistakes in my text.