Why “Normal” Isn’t Always Normal: The Problem With NHS Blood Test Guidelines After Bariatric Surgery

If you’ve had bariatric surgery and you’ve ever been told:

• “Your results are fine.”

• “Everything is within normal range.”

• “You just need to take your vitamins.”

But you still feel tired, foggy, dizzy, or unwell…

You’re not alone. And you’re not imagining it.

The issue is simple: NHS blood test guidelines are not designed for bariatric patients.

They are built for the general population — not people with altered digestion, absorption, or nutritional risk due to weight loss surgery.

Let’s break this down.

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1. The “Reference Range” Problem

When you get a blood test result, you’re compared to a population average — usually made up of people who haven’t had surgery.

But after a gastric bypass or sleeve, your body absorbs nutrients differently. You need different levels to feel well. What’s “normal” for someone else might be far too low for you.

Example:

• Vitamin B12: NHS range is 140–700 pmol/L.

• Many patients are told 180 or 200 is “normal.”

• But bariatric guidelines suggest aiming for >400–500 to prevent nerve damage, fatigue, and cognitive symptoms.

• Ferritin: NHS may say 15 is fine.

• We look for >70–100 in bariatric patients — especially if you’re female or menstruating.

• TSH: May be “normal” at 3.5, but post-op patients often feel best when TSH is closer to 1.0 and Free T3 is optimal.

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2. The Missing Tests

Many GPs will only order:

• TSH (but not Free T3 or Free T4)

• Basic iron or B12

• Maybe Vitamin D

But a proper post-op panel should include:

• Full thyroid profile (TSH, Free T3, Free T4, FTI, T3 Uptake)

• Full iron studies (Iron, Ferritin, TIBC, % saturation)

• B12, Folate, B6, MMA, Homocysteine

• Vitamins A, D, E, K

• Zinc, Copper, Magnesium, Phosphorus, Selenium

• Calcium + Parathyroid Hormone (PTH)

• Protein, Albumin, CRP, Liver and Kidney markers

These are routine in global bariatric follow-up — but rarely ordered in UK primary care unless you advocate hard for yourself.

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3. NHS Cost-Cutting Has Made It Worse

Over the last decade, NHS cost-saving initiatives have meant:

• Less access to certain tests (like Free T3 and Vitamin E)

• More strict interpretation of what’s “worthy” of treatment

• Pressure to reduce prescriptions for expensive supplements

This means that even when you show up with symptoms — they may not run the tests you need or treat you unless you’re severely deficient.

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4. The Result?

Thousands of post-op patients walking around with:

• Undiagnosed deficiencies

• Poor thyroid function despite “normal” TSH

• Hair loss, fatigue, brain fog, mood swings, dizziness

• No one listening — because their bloods are “fine”

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So What Should Be Done?

At Health Check Antalya, we use international post-bariatric guidelines — not general population averages.

Our approach includes:

• Full testing

• Expert interpretation by doctors who understand post-op physiology

• Treatment advice based on you, not outdated cut-offs

We know what “normal” really looks like for someone who’s had surgery.

And we know that feeling well matters more than what the lab computer flags as “green.”

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Need Your Blood Tests Reviewed?

We offer:

• Full in-clinic health checks

• Home testing kits

• Personalised reviews with no judgement or dismissal

Click below to learn more or book a consultation.

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