💊 MMA & Homocysteine Lab Interpretation Simulator

A Borderline Serum B12 Level Rarely Settles the Question

Serum B12 alone is an unreliable proxy for tissue status.

• 200–300: Gray-zone range (pg/mL, ambiguous)
• ~30%: False normal rate (placeholder estimate)
• 2: Binding proteins (transcobalamin, haptocorrin)
• MMA + Hcy: Next step (functional markers)

Why serum B12 misleads at the margins

Placeholder: total B12 mixes active and inactive fractions.

Methylmalonyl-CoA Mutase Needs Adenosylcobalamin to Run

Without B12 cofactor, methylmalonyl-CoA cannot become succinyl-CoA.

• AdoCbl: Cofactor (adenosylcobalamin)
• MUT: Enzyme (methylmalonyl-CoA mutase)
• <270: Normal MMA (nmol/L placeholder)
• High: Specificity (placeholder value)

Placeholder: substrate backup mechanism

Placeholder: blocked mutase step raises upstream MMA levels.

Methionine Synthase Also Depends on Cobalamin

Methylcobalamin loss stalls homocysteine remethylation to methionine.

• MeCbl: Cofactor (methylcobalamin)
• MTR: Enzyme (methionine synthase)
• Folate: Confounder (also raises homocysteine)
• <15: Normal Hcy (µmol/L placeholder)

Placeholder: shared pathway vulnerability

Placeholder: homocysteine rises alongside MMA in true deficiency.

Reading MMA and Homocysteine Together Resolves Ambiguity

Concordant elevation of both markers strengthens the diagnosis.

• High spec.: Both elevated (placeholder value)
• Consider folate: Only Hcy up (placeholder note)
• Renal cause?: Only MMA up (placeholder note)
• Likely normal: Neither up (placeholder note)

Placeholder: interpretation matrix logic

Placeholder: pattern of both markers guides final call.

Tissue-Level B12 Deficiency Confirmed by Functional Markers

Elevated MMA plus homocysteine confirms deficiency despite borderline B12.

• High: Confidence (placeholder value)
• Treat & retest: Next step (placeholder note)
• Good: Reversibility (if treated early)
• 6–8 wks: Monitoring (placeholder interval)

Placeholder: confirming and treating deficiency

Placeholder: repletion should normalize both metabolites over time.

Placeholder: functional markers beat serum B12 alone near cutoffs.