Understand vitamin markers in your lab result

The 25-hydroxyvitamin D test measures the storage form of vitamin D in the blood — the best indicator of overall vitamin D status. Vitamin D is essential for calcium absorption, bone health, immune function, and muscle strength.

Vitamin B12 (cobalamin) is essential for red blood cell production, DNA synthesis, and the health of the nervous system, including the myelin sheath that protects nerve fibres.

Folate (vitamin B9) is essential for DNA synthesis and repair, red blood cell production, and is critically important during early pregnancy to prevent neural tube defects.

Ferritin is a protein that stores iron inside cells. Blood ferritin levels reflect the body's total iron stores and are the most sensitive blood marker for iron deficiency.

Serum iron measures the amount of iron circulating bound to transferrin in the blood. It represents iron in transit between storage and use, not total body iron stores.

TIBC measures the blood's maximum capacity to bind and carry iron. It reflects the amount of available transferrin — the protein that transports iron in the blood.

Transferrin saturation expresses the percentage of transferrin binding sites currently occupied by iron. It is calculated from serum iron and TIBC and reflects the efficiency of iron delivery to tissues.

Parathyroid hormone is produced by the parathyroid glands and regulates calcium and phosphorus balance in the body. It is often reviewed with calcium, vitamin D, phosphorus, magnesium, kidney markers, and clinical context.

1,25-Dihydroxy Vitamin D is the active hormonal form of vitamin D, produced mainly in the kidneys from the storage form (25-Hydroxyvitamin D). It is NOT the standard vitamin D screening test — that role belongs to 25-Hydroxyvitamin D (the "Vitamin D" entry above).