While a lot of us dismiss tiredness, fatigue, and brain fog as usual parts of a busy day, these symptoms, more often than not, signal a hidden deficiency. While most of us would naturally gravitate towards an iron deficiency , the fact of the matter is that a simple ‘serum iron’ test is pretty unreliable when it comes to gauging overall health. So what should one do?



Dr. Sudhir Kumar, a leading neurologist, in a recent tweet, explained that many standard medical tests often miss a hidden deficiency. This hidden deficiency leaves the patients with symptoms like fatigue and brain fog, even when the routine tests are normal. Dr Kumar encourages the doctors and the patients to look beyond the tests, to find the underlying problems… Let’s see how…







The problem with routine medical tests

Common medical investigations such, as CT scans, endoscopy, stool tests and blood tests, often come back normal when patients have health problems such as cramps, and other deficiencies, since these tests mainly look for infections, inflammation or organ damage, while skipping nutrient, or metabolic deficiencies. As Dr Kumar says, “Stop Relying on “Serum Iron” Alone; It Often Misleads.”




Here's what truly matters

Dr Kumar says, “Most people (and many lab panels) still focus on serum iron to assess iron deficiency.

But here is the truth:

Serum iron is unreliable.

It fluctuates through the day, varies with food intake, and tells us almost nothing about how much usable iron the body actually has.”




Ferritin : The key to uncovering hidden iron deficiency

Dr. Sudhir Kumar says the ferritin test is important, when it comes to gauging overall health. Ferritin is a protein that stores iron in the body and ferritin levels in the blood, show how much iron is stored. Normal serum iron tests only measure iron that is moving in the blood, and the tests do not show if iron stores are low. However, a low ferritin level shows iron deficiency, even when serum iron looks normal. This deficiency can cause tiredness, weakness and nerve problems without the signs of anemia. As Dr Kumar says, “Low ferritin = true (absolute) iron deficiency. But ferritin rises in inflammation, infection, obesity, and chronic disease.”




TSAT ( Transferrin Saturation ): Another crucial iron test

Besides ferritin, Dr. Kumar talks about the TSAT or transferrin saturation test. Transferrin is a protein that moves iron in the blood, and TSAT tells how much iron is attached to the transferrin. When TSAT is low, the iron supply to the tissues is weak, even if the blood iron looks normal. Like ferritin, TSAT helps find iron deficiency in such cases. “Low TSAT = your tissues are not getting enough iron. Even if ferritin is normal or high, low TSAT can indicate functional iron deficiency”, says Dr Kumar.




CRP ( C-Reactive Protein ): Detects hidden inflammation in the body

C‑Reactive Protein (CRP) is also a test Dr. Kumar recommends. The key to spotting inflammation, CRP measures the level of inflammation in the body, and many routine tests do not detect that inflammation. Chronic low grade inflammation can cause fatigue and other symptoms, and can even affect the heart. CRP helps identify whether underlying inflammatory processes contribute to symptoms and guides evaluation. Dr Kumar says,



“Helps interpret ferritin correctly.

High CRP + high ferritin + low TSAT = inflammation blocking iron availability.”







Why these tests are important

According to Dr Kumar

“Iron deficiency (true or functional) can contribute to:

1. Fatigue

2. Brain fog

3. Restless legs

4. Worsening of chronic neurological symptoms

5. Reduced exercise tolerance

6. Poor immunity”




What should one ask for



According to Dr Kumar, next time you get an iron check, request:

“Ferritin

Transferrin Saturation (TSAT)

CRP

Not just “serum iron.”

These three together give a complete and accurate picture of your iron health.

Better testing → Better diagnosis → Better energy → Better brain health.”




Limitations

According to Dr Kumar, these tests come with some issues as well. He says,



“1. While ferritin + TSAT + CRP is very informative, they are not perfect. Other markers (for ex-soluble transferrin receptor, reticulocyte hemoglobin content) may be needed in complex cases.



2. Cut-off values for ferritin or TSAT to define iron deficiency can vary depending on context (e.g., chronic disease, heart failure, kidney disease).



3. In patients with very high ferritin (for ex-due to inflammation or liver disease), interpretation requires caution because of potential iron overload or misdiagnosis.”