Normal Blood Calcium Levels Adjusted for Patient's Age

Blood calcium levels vary as we age, but labs don't give normal calcium ranges according to age. The highest blood calcium levels are seen between the ages of 15 and 25.  Adults over 40 should not have calcium levels above 10.1 mg/dl.

High blood calcium is never normal. Unfortunately, very few doctors understand that the normal range for blood calcium changes as we age. This graph shows how blood calcium levels increase normally as we go through puberty and our growth spurt. The highest blood calcium levels occur in our teenage years and early twenties, shown as the increase in the height of the green area during these years.

This parathyroid blog covers one of the two most common mistakes we see doctors make regarding the diagnosis and understanding of hyperparathyroidism… those two are 1) it is the duration of high calcium that hurts people, not how high the calcium has become (covered in another blog), and the problem covered here: 2) Blood calcium levels change as we age and labs do not report the normal ranges according to the patients age. Keep reading and see why this is such a huge problem leading to about 1/2 of people with hyperparathyroidism not being aware that they have it. We are not doctor-bashing here. Some of this is not the fault of the doctor, rather the labs are not reporting normal ranges correctly. How is the doctor supposed to know?

Almost all of our lab values are the same for children, teens, adults, and us old guys.  The amount of chloride, sodium, potassium, magnesium, etc, etc, is the same for all age groups. Blood calcium levels is the big exception. The reason the blood calcium levels increase during the teenage years is because of the normal growth spurt that occurs. There is a lot of bone growth and bone cell "turnover" as new bone is formed and the bones get stronger and more dense. During these years of active bone formation and maturation, blood calcium levels are the highest.  The graph above very clearly shows a big increase in blood calcium during the teenage years lasting into the 20's, and then decreasing until age 35 or so when adults should have all (or almost all) of their blood calcium levels "in the 9's".

Rules for Normal Blood Calcium Levels:

• Teenagers and young adults are supposed to have blood calcium levels in the low 10's
• Adults over 35 should have blood calcium levels in the 9's.
• Adults over 40 are not allowed to have calcium levels "in the 10's". (rarely is ok, but not frequently, and not over 10.2)
• Although some labs will report the lower range of blood calcium to be about 8.8 mg/dl, this is rarely true. Almost everybody, regardless of age should have calcium levels above 9.0 mg/dl.
• Almost all adults over 35 have blood calcium levels between 9.4 and 9.9 mg/dl.  9.7 is the most common blood calcium level (the mode).
• For our friends outside the US:  To convert mg/dl to mmol/L: Multiply by 0.2495.  To convert mmol/L to mg/dl:  Divide by 0.2495. Thus a calcium 10.0 mg/dl = 2.495 mmol/L.  A calcium of 11.0 mg/dl = 2.75 mmol/L

- THE BLOOD CALCIUM PROBLEM -

The big problem is that labs will typically give your blood calcium level and then give the "normal range" for ALL HUMANS. In other words, the lab will say the normal range is between 8.8 and 10.6 mg/dl.  Well this is true for ALL humans, but it is NOT true if you are over 35 years old. The photo to the left is a perfect example. This is from a 52 year old woman that I consulted with today. She has all the classic symptoms of hyperparathyroidism but her doctors had absolutely no clue that she had this disease because the lab was providing a normal range for her calcium for ALL humans, not a 52  year old woman! As you can see, from 2000 on she has had calcium levels "in the 10's", but her lab usually gives normal ranges of 10.5 to 10.8 mg/dl.  I have to admit, her doctors could have picked up on this, but every time they thought her calcium was high, the next level a year or so later showed the calcium to be "normal". This is a problem we see in about 90% of the charts we review. The labs give a normal range for all humans (most of the time), so the calcium levels "in the 10's" are not appreciated. You can see that her first and last labs were done at a different laboratory, where the normal range was given as 10.2 mg/dl. This lady diagnosed hyperparathyroidism herself. She got a copy of her labs, realized that a calcium level of 11.0 was high, so she typed "high blood calcium" into Google and guess what she found?  Why do patients have to diagnose themselves with tumors? Where are our doctors??

Since most doctors are not aware that blood calcium levels are different for different ages (heck, we were never taught this either!), they will see your calcium level of 10.5 and say "your calcium is fine… it is in the normal range".  If you are over 35, however, nothing could be further from the truth, but nobody is aware because the lab did not give the normal range for somebody your age (which is 9.0 to 10.0 for all adults over 40). As you will learn by reading more about hyperparathyroidism, the height of the calcium (how high it has become) is a very poor predictor of the severity of this disease. It is the duration (how long it has been over 10.0 mg/dl) that is associated with all of the complications of high calcium.

The High Blood Calcium Test: Which is worse?

Question: Who has the worst hyperparathyroidism, a woman with a calcium of 12.2 mg/dl or a woman with a calcium of 10.8 ???  The answer is- you cannot tell when all you know is how high the calcium has become. The person with the "worst" hyperparathyroidism (the one with the biggest damage to their bones, heart, arteries, muscles, kidneys, etc) is the one that has had blood calcium levels that are elevated the longest. The person with the higher calcium is not necessarily the one with the worst disease! Remember, we measure the severity of hyperparathyroidism by the damage it has produced which ALWAYS is due the DURATION the parathyroid tumor has been in existence. The person with calcium levels above 10.0 mg/dl the longest is usually the person with the highest number of complications and the one that has the more severe disease.  It is incorrect to assume that a calcium of 12.2 comes from a tumor that is older than one resulting in a blood calcium level of 10.8 mg/dl. And, of course, when your doctor says "your calcium is not that high, let's watch it to see if it goes any higher" you know it is time to stand up and start teaching (or walk out). How high the calcium has become is NOT a good indicator of the severity of primary hyperparathyroidism! This topic is covered in a number of our different blogs.

Want to teach your doctor?  Print the graph at the top of this page and take it to him/her.  Most doctors don't understand that calcium levels of 10.2-10.6 mg/dl in an adult over 40 means they have a parathyroid tumor that will make them miserable… and will cause lots of problems in the coming years. It isn't the fault of the doctor-they were never taught; and the labs don't help by giving wrong normal ranges.  Help us teach!

See the next two graphs that go with this graph on our new parathyroid.com page.

Want to know more? We put a new page on Parathyroid.com about this graph, and TWO more graphs that go with it. The two additional graphs put patients with hyperparathyroidism onto this graph.  http://www.parathyroid.com/Normal-Blood-Calcium-Levels.htm

• See our blog discussing the importance of the "duration" of high calcium causing problems, not how high the calcium has become.
• See our blog discussing how 10 or more years of "slightly elevated" calcium (in the 10's) can have an effect like cancer on your body.
• See the blog with all the medical journal articles showing how years of high calcium is more deadly than high cholesterol.