How It Is Used

• The test can be used to diagnose thyroid disorders, infertility problems and pituitary function. It can also be used to screen newborns for underactive thyroid and monitor the effectiveness of thyroid medication.
  
  

Normal Ranges

• Normal ranges for TSH levels are 0.4 to 4.0 mlU/L according to Medline Plus. But for those with signs of underactive thyroid, a value of over 2 mlU/L may indicate future hypothyroidism.
  
  

Abnormal Results

• High readings may indicate hypothyroidism, or an underactive thyroid. Low readings may indicate hyperthyroidism. Additional testing is usually required to finalize a diagnosis and determine the cause.
  
  

The Test

• The test is performed by taking a blood sample from a vein or artery through a needle. Complications are rare but can include excessive bleeding, fainting, bruising and infection.
  
  

Considerations

• Certain medications, including aspirin, can affect the test readings, so inform your doctor about any medications or supplements you are taking. Extreme stress and illness can also affect the results.