This is a fictional, illustrative case created for education. It is not medical advice, diagnosis, or treatment, and does not describe a real person.

The mystery fatigue her "normal" blood test missed

Maya, 38: exhausted, flat, and tingling for a year while every test looked normal. The clue was not in how much B12 she had — it was in how much her cells could use.

Persona

Maya, 38, Female, West African, Knowledge worker.

A year of exhaustion, low mood, and buzzing in her hands and feet, even though her blood work keeps being called normal.

Family history: Mum has always been tired. Dad had a heart attack at 58; his doctor flagged unusually high levels of a compound called homocysteine.

Clinical picture

Symptoms

Labs

Medications

Supplements

Lifestyle

Genetics

A year of feeling unwell on paper

Maya is 38, generally healthy, and takes no medications. For a year she has woken up tired, lost her usual spark, and felt a strange buzzing in her fingertips and the soles of her feet. Her family doctor ran the usual blood work. Everything landed inside the reference range. On paper she was fine. In real life, she was not.

The numbers that hid the clue

Her B12 and folate were both technically normal, so nothing was flagged. But a standard blood test shows what is circulating in the blood. It does not prove that enough B12 and folate are getting absorbed, activated, and used inside cells. That is where the mystery starts to make sense.

Two clues were already there

Two details change the picture. She moved to a mostly plant-based diet 18 months ago, cutting back her main food source of B12 just before the symptoms began. Her dad's high homocysteine is another clue: that compound can build up when the same B12 and folate pathway is not running smoothly. The clues point in one direction.

Her blood looked fine. Her cells didn't.

The issue was not whether Maya cared enough or ate the right foods. The issue was absorption and activation. Her FUT2 result helps explain why less B12 may reach her system, and her MTHFR results help explain why folate processing is slower once it gets there. Her B12 of 215 pg/mL sits inside the lab range, but that does not prove her cells have enough usable B12 and folate. This is how she can feel exhausted, flat, and tingly while the standard labs look fine.

The supplement clue

The supplement looked helpful, but it may not have matched her biology. Her pharmacy B-complex contains folic acid, a synthetic form of folate that people with MTHFR variants may convert less efficiently. For Maya, the better question is not "more B vitamins?" but "which forms can my body actually use?" Her dad's high homocysteine fits the same pathway, making this a family pattern worth discussing.

What Maya brings to her clinician

Maya's check-in: 14 days of tracking

Daily energy & tingling check-in. Maya logged energy and tingling every morning. The first week looked the same as always. After she switched to methylcobalamin on day 8, the pattern finally started to move.

The week the pattern changed

Each square is one day. Darker red means worse. Green means a better day. Gray means not logged. Week 5 is when Maya switched supplements.