Low vitamin B12

Clinically: Vitamin B12 deficiency · also cobalamin deficiency, low B12, pernicious anaemia

nutritional ICD-10 E53.8 MONDO MONDO:0020696 unverified

This describes what this condition typically looks like. It is not a diagnosis and cannot tell you whether you have it -- patterns overlap, results vary between labs, and the same numbers mean different things in different people. Diagnosis usually rests on Cobalamin, interpreted alongside symptoms and history rather than read off a report. Note that a normal-looking result does not reliably rule this out -- see the caveats above.

unverified These explanations are written to be easy to read and have not yet been checked against a source. The ranges and measurement notes on this page show theirs.

definition unverified

Your body is short of vitamin B12, which it needs both to build red blood cells and to maintain the insulating layer around your nerves.

Inadequate vitamin B12 status from insufficient intake or impaired absorption (e.g. loss of intrinsic factor in pernicious anaemia), presenting with megaloblastic anaemia and/or neurological involvement. Serum B12 below 148 pmol/L is commonly considered to suggest frank deficiency and 148-220 (or 260) pmol/L mild deficiency, but 30-40% of symptomatic patients may have normal serum concentrations.

caveats unverified

This one matters to catch early. The blood effects reverse with treatment, but nerve damage from a long shortage may not. Symptoms can appear while the blood level still looks acceptable, so nerve symptoms with a borderline result are usually worth acting on rather than dismissing.

No clinical version written yet.

How common it is

Rises with age and is common in people who eat little or no animal food, who take long-term acid-reducing or diabetes medication, or who have had gut surgery.

The typical lab pattern

What the diagnosis rests on

The results a diagnosis is actually made on.

Cobalamin

low

—

Below 148 pmol/L is commonly taken as clear deficiency, and 148-220 (or 260) pmol/L as mild; but 30-40% of people with symptoms have a normal level.

Consistent with it

Fits the picture, but not enough on its own.

Mean corpuscular volume	high	—	Red cells are larger than normal (adult cut-off 100 fL). About 1 in 4 patients have this masked by iron deficiency or thalassaemia trait.
Hemoglobin	low	—	Anaemia (low haemoglobin) with large red cells is the most common blood finding, though nerve problems can occur without anaemia.
Lactate dehydrogenase	high	—	Raised because red-cell precursors are destroyed inside the bone marrow; it can be very high.
Bilirubin, total	high	—	Red-cell precursors break down inside the bone marrow, which can raise bilirubin (the indirect form) and LDH, so the picture can look like haemolysis.

How it usually feels

Frequencies say how often a symptom accompanies this condition — not the other way round. Most people with any of these symptoms do not have this.