Serum Phosphorus Blood Test

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A serum phosphorus blood test is performed to determine how much phosphorus a patient has in his or her blood. This test may also be referred to as inorganic phosphate, phosphors – serum, or phosphorus blood test. This test may also be performed to aid in diagnosis or to monitor a medical condition.

Why is this Test Performed?

This test is performed to measure blood-phosporus levels. If a patient’s doctor feels this may be abnormal, either too low or too high, they will often order this blood test. If a doctor knows or suspects that a patient has a medical condition that could cause abnormal phosphorus levels, they will often order this test.

Preparation and Procedure

Preparation is not always necessary for a serum phosphorus blood test. However, if a patient is taking certain drugs, they may have to either temporarily stop taking the drug or adjust the dosage before having this test done so that the results are not affected. The following drugs and medications may affect the test results:

  • Antacids
  • Excess vitamin D supplements
  • Laxatives that contain sodium phosphate
  • Enemas that contain sodium phosphate
  • Intravenous glucose
  • Methicillin

How this test feels will depend on the patient. For most patients a stinging or prick is all they feel, if anything at all. However, a small amount of patients may experience moderate pain or discomfort.

For this test a blood sample is necessary. To obtain this, a health care provider will use a needle and insert it into a vein. An airtight vial will then collect enough blood to test for the patient’s phosphorus levels. Younger children and infants will most often have a blood sample taken through using a lancet to prick the skin. The blood will be collected onto a slide, test strip, or pipette. A bandage is then applied to the puncture site.


If the results of this test are normal, the ranges will be about 2.4 to 4.1 milligrams per deciliter, mg/dL.

If the test reveals that the patient has higher than normal blood-phosphorus levels, referred to as hyperphosphatemia, it may indicate:

  • Bone metastasis
  • Hypocalcemia
  • An increase of intravenous or dietary phosphorus intake
  • Renal failure
  • Too much vitamin D
  • Diabetic ketoacidosis
  • Hypoparathyroidism
  • Liver disease
  • Sarcoidosis
  • Using certain medications like laxatives that contain phosphate

If the test reveals that the patent has lower than normal blood-phosphate levels, referred to as hypophosphatemia, it may indicate:

  • Hypercalcemia
  • Hyperparathyroidism
  • Not getting enough dietary vitamin D or phosphate, resulting in osteomalacia in adults or rickets in children
  • Hyperinsulinism
  • Malnutrition

This test may also be performed if the patient’s doctor suspects the following:

  • Secondary hyperparathyroidism
  • Multiple endocrine neoplasia
  • Tertiary hyperparathyroidism


University of Maryland Medical Center. (2010). Serum Phosphorus Overview. Retrieved on November 25, 2010 from the University of Maryland Medical Center:

MedlinePlus. (2009). Serum Phosphorus. Retrieved on November 25, 2010 from MedlinePlus: