TOTAL THYROXINE (TT4)

25-OH VITAMIN D (VITD)

Best indicator of overall vitamin D status, used to evaluate deficiency or insufficiency affecting bone health, calcium metabolism, and immune function.

LIS TEST CODE: VITD

CPT CODE: 82306

ALIASES: Vitamin D, 25-Hydroxy D2, 25-Hydroxy D3, 25-Hydroxy Vitamin D, 25-Hydroxycholecalciferol, Calcidiol, 25OHD, Calciferol, Ergocalciferol

METHODOLOGY: Chemiluminescent Microparticle Immunoassay (CMIA)

SPECIMEN:

- Type: Serum

- Container: Gold Top (SST) Vacutainer

- Minimum Volume Required: 1 mL

- Storage/Handling: Allow 30 minutes for blood to clot, then centrifuge specimen at 3500 RPM for 10 minutes. Maintain specimen at room temperature or in the refrigerator until testing can be performed.

- Stability:

Room Temperature (20-25 °C): 3 days

Refrigerated (2-8 °C): 12 days

Frozen (-20 °C or colder): Not Accepted

- Turnaround Time: 24 hours from receipt.

Special Instructions: If testing will be delayed for more than 3 days, remove serum from the separator gel and transfer into a separate plastic screw-cap transport container.

REJECTION REASONS: QNS, Gross Hemolysis, Gross Lipemia, Contamination, Stability Violation, Expired Container, Incorrect Container

REFERENCE RANGES:

Males & Females (ng/mL)

>= 1 years of age: 20.0 - 50.0

Total 25-hydroxyvitamin D

Severe deficiency: < 10.0 ng/mL*
Mild to moderate deficiency: 10.0 - 19.0 ng/mL**
Optimum levels: 20.0 - 50.0 ng/mL***
Increased risk of Hypercalciuria: 51.0 - 80.0 ng/mL****
Toxicity possible: > 80.0 ng/mL*****

*Could be associated with osteomalacia or rickets.
**Might be associated with increased risk of osteoporosis or secondary hyperparathyroidism.
***Optimum levels in the healthy population.
****Sustained levels > 50.0 ng/mL 25OH-VitD along with prolonged calcium supplementation may lead to hypercalciuria and decreased kidney function.
*****80.0 ng/mL is the lowest reported level associated with toxicity in patients without primary hyperparathyroidism who have normal kidney function. Most patients with toxicity have levels > 150.0 ng/mL. Patients with kidney failure can have very high 25-OH-VitD levels without any signs of toxicity, as renal conversion to the active hormone 1,25-OH-VitD is impaired or absent.