26 April 2026
: Case report 
Metformin-Associated Functional Vitamin B12 Deficiency Presenting as Subacute Combined Degeneration in a 57-Year-Old Man With Diabetes Mellitus
Unusual clinical course, Challenging differential diagnosis, Rare coexistence of disease or pathology
Ruixiang Zhang ABCDEF 1,2,3, Luoning Gou ADFG 1,2,3*, Xinrong Zhou ABCDG 1,2,3DOI: 10.12659/AJCR.952205
Am J Case Rep 2026; 27:e952205
Table 1 Laboratory examination results on admission.
| Parameter | Values | Parameter | Values |
|---|---|---|---|
| RBCs | 3.49×10/L (4.3–5.8) | FBG | 7.8 mmol/L |
| Hemoglobin | 115 g/L (130–175) | Insulin | 13 μIU/mL |
| MCV | 90 fL (82–100 fL) | C-peptide | 5.21 ng/mL |
| MCH | 33 pg (27–34) | PCA | 0.78 U (≤20) |
| MCHC | 366 g/L (316–354) | IFA | 1.5 U (≤20) |
| Vitamin B12 | 319 pg/mL (180–914) | ACTH | 6.3 pg/mL (7.2–63.3) |
| Folate | 6.48 ng/mL (≥4) | CORT (12 AM) | 8.8 μg/dL (6.7–22.6) |
| Homocysteine | 18.4 μmol/L (0–15) | CORT (8 AM) | 14.9 μg/dL (6.7–22.6) |
| pH | 7.342 (7.35–7.45) | CORT (4 PM) | 19.9 μg/dL (2.0–14) |
| pCO | 28.7 mmHg (35–45) | eGFR | 50.8 mL/min/1.73 m (>90) |
| pO | 114 mmHg (80–100) | Cr | 133 μmol/L (45–84) |
| AB | 15.1 mmol/L (21–28) | BUN | 9.7 mmol/L (3.1–8.0) |
| SB | 17.4 mmol/L (21–25) | β-HB | 6.6 mmol/L (0.02–0.27) |
| BE | −8.9 mmol/L (−3 to 3) | Urinary ketones | 2+ |
| BEecf | −9.5 mmol/L (−3 to 3) | ||
| AB – actual bicarbonate; ACTH – adrenocorticotropic hormone; BE – base excess; BEecf – base excess of extracellular fluid; BUN – blood urea nitrogen; CORT – cortisol; Cr – creatinine; eGFR – estimated glomerular filtration rate; FBG – fasting blood glucose; IFA – intrinsic factor antibody; MCH – mean corpuscular hemoglobin; MCHC – mean corpuscular hemoglobin concentration; MCV – mean corpuscular volume; PCA – parietal cell antibody; RBCs – red blood cells; SB – standard bicarbonate; β-HB – β-hydroxybutyrate. | |||