What Is a Phosphate Blood Test?
A phosphate test measures the amount of phosphate in your blood. Phosphate is what you get when you combine the mineral phosphorus with oxygen. When you eat certain foods — such as beans, nuts, cereal, milk, eggs, beef, chicken, and fish — phosphorous enters your intestines. When it meets up with oxygen, it becomes phosphate.
Most phosphates team up with calcium to build and repair your bones and teeth. Some support your muscles and nerves.
Here's where things get tricky: When it comes to testing, phosphorus is sometimes called phosphate and vice versa. Don’t let all those “ph-ph” words confuse you.
Why Do I Need a Phosphate Blood Test?
Though you absorb phosphate in the intestines, it's filtered and removed through your kidneys.
Abnormal phosphate levels — with symptoms such as bone problems, fatigue , and weakness — may point to a kidney disorder. Your doctor may also want you to get a phosphate test if they suspect:
- Issues with diabetes
- Hormone imbalances, such as vitamin D or PTH, a hormone that helps balance calcium and phosphorus in your body
- Malnourishment
Since phosphate works so closely with calcium, doctors also use the test to figure out whether your body is getting and using calcium the right way. Issues related to calcium can be a sign of low vitamin D, or they may include:
- Bone problems
- Feeling very tired
- Muscle weakness
- Cramping
Preparing for a Phosphate Blood Test
Your doctor will give you instructions; follow them carefully. They may ask you not to eat anything from midnight before the test until after the test is over.
Make sure your doctor knows about everything you're taking, including prescription and over-the-counter medicine, herbal supplements, vitamins, and recreational or illegal drugs.
What Happens During a Phosphate Blood Test?
After cleaning the skin on part of your arm, a health care professional will insert a needle into one of your veins. They may wrap an elastic band around the upper part of your arm to make that vein easier to find.
Once enough blood goes into a tube, the technician will take off the band, pull out the needle, and stop the bleeding with a cotton ball or bandage. They’ll label the tube of blood and send it to a lab.
With any blood test, you may feel:
- Pain when the needle is inserted
- Dizziness
- Soreness or bruising
- Bleeding
What Can Affect My Test Results?
If you've had dialysis, it may affect your phosphate levels, as can some medicines. Some things you eat and drink might have an effect, too, so check with your doctor about whether to avoid these before the test:
- Beans (many different kinds)
- Beer
- Cheese
- Chocolate
- Cola
- Fish
Some medicines, vitamins, and supplements can impact your test results' precision. These can include diuretics (water pills), antacids, and laxatives. Tell your doctor about everything you’re taking, including nonprescription medications. But continue to take prescribed medicines unless your doctor tells you to stop.
Phosphate Blood Test Results
Here's what the numbers on your phosphate blood test mean:
Low phosphate (hypophosphatemia)
- Below 2.5 mg/dL
Normal phosphate
- 2.5 to 4.5 mg/dL for adults
- 4.5 to 6.5 mg/dL for children
Hyperphosphatemia (high phosphate)
- Above 4.5 mg/dL
These ranges might vary slightly depending on the lab that is doing the testing.
What Do My Test Results Mean?
When the results are too high or too low, it's a sign that something's not right.
Low phosphate in blood test
If your phosphate levels are low, it may be a sign of:
- Alcoholism
- Severe burns
- Diabetic ketoacidosis (too much acid in the blood)
- Overuse of diuretics (drugs that remove excess fluid from the body)
- Using too much antacid
- Hypercalcemia (too much calcium in your blood)
- Hyperparathyroidism (high levels of the parathyroid hormone)
- Malnutrition
- Vitamin D deficiency conditions, such as rickets
High phosphate in blood test
High phosphate levels may be a sign of:
- Hypoparathyroidism (low levels of the parathyroid hormone)
- Cardiovascular disease (disorders of the blood vessels or heart)
- Cell lysis
- Laxative overuse
- Liver disease
- Kidney failure or injury
- Osteoporosis (a condition that causes brittle and weak bones)
- Vitamin D overuse
What Other Tests Might I Have?
Your doctor may give you other tests along with the phosphate blood test to help narrow down their diagnosis. These can include tests for:
- Calcium
- Vitamin D
- PTH (hormone produced by the parathyroid gland)
Phosphate urine test
This test checks the amount of phosphate in a urine sample collected over 24 hours. You may need this test if you have:
Symptoms of kidney problems
A history of kidney stones
An electrolyte imbalance
Abnormal calcium test results
You’ll need to collect all your urine over 24 hours. Here’s what to do:
- Start by peeing in the toilet as usual, but don’t collect that sample. Note the time.
- Collect all your urine over the next 24 hours in a special container your doctor provides.
- Keep the container cool, either in a refrigerator or on ice.
- After 24 hours, pee one last time and collect that sample.
- Return the container to your doctor or lab.
Your doctor will explain whether your levels are normal, low, or high, considering your health and age. They might order both blood and urine tests to find out how well your kidneys are processing phosphate.
Takeaways
A phosphate blood test checks the level of phosphate in your blood, which is essential for strong bones and teeth and muscle and nerve support. High or low phosphate levels point to various health issues. You might need a test if your doctor suspects kidney problems, diabetes, hormone imbalances, malnourishment, or low calcium levels.
Phosphate Blood Test FAQs
What is alkaline phosphatase in blood tests?
Alkaline phosphatase (ALP) is an enzyme present in many parts of your body. An ALP blood test checks the amount of this enzyme in your blood, mainly from your liver and bones. High levels may be a sign of liver disease or a bone disorder.
Why do I need a phosphorus blood test?
This test checks your phosphorous levels; an abnormal level could mean kidney, liver, or bone disease.