An Overlooked Way To Test For Vitamin D - Dominick Hussey

An Overlooked Way To Test For Vitamin D

Vitamin D is critical for health. It promotes calcium absorption in the gut and helps maintain calcium and phosphate levels in the blood. This, in turn, enables proper bone health and protects against osteoporosis, rickets, and fracture; but it also plays a number of other important roles in the body, including regulating cell growth, neuromuscular function, and immune function. So using an accurate measure to test for vitamin D is important.

The most common blood marker used to determine vitamin D status is 25(OH)D, and the reference range for this marker in the United States is 30 ng/ml to 100 ng/ml. This converts to 75 nmol/l to 250 nmol/l in Canada.

The problem with this range is that 25-D is not the biologically active form of vitamin D and is thus not the best marker for biological vitamin D activity. That means it’s possible for someone to have a normal 25-D level and still be biologically deficient.

In this article, I’m going to talk to you about an often overlooked lab marker, parathyroid hormone, or PTH, which more accurately diagnoses vitamin D deficiency. Armed with this information, you will better equipped to test for vitamin D deficiency.

How I discovered PTH?

I learned about using PTH to test for vitamin D while doing some training with Chris Kresser, a Functional Medicine Practitioner and one of the sharpest people I follow in the functional medicine space.

Why use PTH to test for Vitamin D?

The conversion of 25-D, the inactive form of vitamin D, to 125-D, or calcitriol, the active form, is tightly regulated by parathyroid hormone. Parathyroid hormone increases calcitriol formation and thus increases serum calcium by acting on the kidneys and bone. Generally speaking, PTH levels will be high when vitamin D is low, since the body is producing more PTH to increase calcitriol formation, and PTH levels will be low when vitamin D levels are sufficient because of negative feedback of vitamin D suppressing PTH output.

What is an optimal range for PTH?

The typical PTH lab reference range is between 10 and 65 pg/ml. That’s what’s considered normal.

A study of vitamin D-suppressing effects of PTH showed the greatest effect when PTH was over 49. In that situation, taking vitamin D reduced PTH by 21 pg/ml. With PTH at a baseline of 38 to 49, taking vitamin D reduced PTH by 17 pg/ml, and with a baseline, PTH of 6 to 38, taking vitamin D only dropped PTH by 2 pg/ml.

So what does all of this mean?

If you have a 25-D level of 35 ng/ml (87 nmol/l), that would technically be normal according to the reference range. But if your PTH is 50, you can be fairly certain that you are biologically deficient despite having a normal 25-D level.

If your PTH is 35, it’s less clear, but since her 25-D is at the bottom of the range, supplementing with vitamin D until your PTH drops below 30 is probably still a good idea in those situations.

Why would a person with normal 25-D levels be biologically deficient?

We now know that there are several factors that affect the biological activity of vitamin D. These include:

  • Ethnicity and genetics, which impact the conversion of 25-D (the inactive form) to calcitriol, or 125-D (the active form);
  • Inflammation and obesity, which reduce the conversion of sunlight to vitamin D; and
  • Gut health, which affects the absorption of orally consumed vitamin D, among others.

These factors can sometimes explain seemingly unusual findings like seeing someone with a 25-D of 112 nmol/l, which is well within the normal range, but then a PTH that’s 55, which is well above 30, which is the level that indicates maximal suppression of PTH by vitamin D.

How using PTH helped a client?

I had one patient like this. He was overweight and had Rheumatoid arthritis. When I supplemented him with vitamin D and also got him more sun exposure, his 25-D went up to 150 nmol/l and his PTH went down to 32. I now include serum PTH in my basic blood chemistry work up with new patients because I find it so helpful in this regard.


Okay, let’s review what we’ve covered in this article.

25-D is the most commonly measured marker of vitamin D status, but it’s not a good indicator of biological vitamin D activity, and it can miss a lot of people who are deficient.

Serum parathyroid hormone reflects biological vitamin D activity and can be used to catch people who are deficient in vitamin D who would otherwise be missed.

A PTH level below 30 indicates that the patient is not deficient in vitamin D, whereas a PTH value above 30 suggests that the person may be biologically deficient even if their 25-D levels are in the reference range.



This article is not intended to provide medical advice, diagnosis or treatment.

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Iron Deficiency Anaemia: Everything you need to know

This blog is the most comprehensive guide to iron deficiency anaemia ever. In this guide, you will learn everything you need to know about the causes, symptoms, diagnosis, and treatment of iron anaemia.

According to Health Canada, around 20% of women and 50% of pregnant women are iron deficient, while only 3% of men are iron deficient in Canada. According to the World Health Organisation, the prevalence of anaemia should be less than 5% and is defined as a moderate problem if the prevalence is 20% to 39.9% and a severe problem when the prevalence is 40.0% or higher. Therefore, by definition, there are populations in Canada in which iron deficiency anaemia is undoubtedly a public health problem.

The question is: If you have an iron deficiency, what can you do about it? Well, that is where this guide comes in.

Chapter 1: What is iron deficiency anaemia?

Anaemia occurs when you have a level of red blood cells (RBCs) in your blood that is lower than normal.

Iron deficiency anaemia is the most common type of anaemia, and it occurs when your body doesn’t have enough of the mineral iron.

Your body needs iron to create a protein called haemoglobin. This protein is responsible for transporting oxygen to your body’s tissues, which is essential for them to function effectively.

When there isn’t enough iron in your bloodstream, the rest of your body can’t get the amount of oxygen it needs.

Chapter 2: What causes iron-deficiency anaemia?

1. Low Iron Intake

Consuming too little iron over an extended amount of time can create a shortage in your body.

Foods such as meat, eggs, and some green leafy vegetables are high in iron.

Because iron is imperative during times of rapid growth and development, pregnant women and young children may require even more iron-rich foods in their diet.

2. Pregnancy or Blood Loss Due to Menstruation

In women of childbearing age, the most prevalent causes of iron deficiency anaemia are heavy menstrual bleeding and blood loss during childbirth.

3. Internal Bleeding

Specific medical conditions can cause internal bleeding that can lead to iron deficiency anaemia. Examples include a stomach ulcer, Intestinal polyps, or colon cancer.

Frequent use of pain relievers, such as aspirin, can also cause bleeding in the stomach.

4. Inability to Absorb Iron

Certain disorders that affect the intestines can also interfere with how your body absorbs iron.

Even if you get enough iron in your diet, the following conditions may limit iron absorption:

  • Celiac disease
  • Non-celiac gluten sensitivity
  • SIBO
  • Achlorhydria (low stomach acid)
  • Parasites

Chapter 3: What Are the Symptoms of Iron Deficiency Anaemia?

The symptoms of iron deficiency anaemia can be very mild at first, and you may not even notice them.

According to the American Society of Hematology (ASH), most people don’t apprehend they have mild anaemia until they have a blood test.

The symptoms of moderate to severe iron deficiency anaemia include:

  • general fatigue
  • weakness
  • pale skin
  • shortness of breath
  • dizziness
  • strange cravings to eat items that aren’t food, such as dirt, ice, or clay
  • a tingling or crawling feeling in the legs
  • tongue swelling or soreness
  • cold hands and feet
  • fast or irregular heartbeat
  • brittle nailsheadaches
  • lower back pain

Chapter 4: How Is Iron-Deficiency Anaemia Diagnosed?

Your doctor can diagnose anaemia with blood tests.

A Complete Blood Count

A Complete Blood count (CBC) test is usually the first test a doctor will use.

A CBC test measures the amount of all components of the blood, including:

  • red blood cells (RBCs)
  • white blood cells (WBCs)
  • haemoglobin
  • hematocrit
  • platelets

The CBC test provides information about your blood that helps diagnose iron deficiency anaemia. This information includes:

  • the hematocrit level, which is the per cent of blood volume that is made up of RBCs
  • the haemoglobin level
  • the size of your RBCs

In iron deficiency anaemia, the hematocrit and haemoglobin levels are low.

Also, RBCs are usually smaller in size than normal.

A family doctor will usually perform a CBC test as part of an annual physical examination.

It’s a good indicator of a person’s overall health and may also be performed routinely before surgery.

This test is useful to diagnose this type of anaemia since most individuals who have an iron deficiency don’t realise it.

Other Tests

Anaemia can usually be confirmed with a CBC test.

Your doctor might order additional blood tests to determine how severe your anaemia is and assist in identifying treatments, including:

  • Iron level in your blood
  • Ferritin levels – Ferritin is a protein that helps with iron storage in your body. Low levels of ferritin indicate low iron storage.
  • Total iron-binding capacity (TIBC)
  • Transferrin – Transferrin is a protein that transports iron. A TIBC test is used to determine the amount transferrin that’s carrying iron.

What if you have symptoms of low iron, but your doctor says your test results are normal?

If you suspect low or high levels of iron, then check your ferritin test result. The ideal range of ferritin is 50 to 70 ng/ml.

Chapter 5: What Are the Potential Health Complications of Iron Deficiency Anemia?

Most cases of iron deficiency anaemia are mild and don’t cause complications.

The condition can usually be easily corrected.

However, if anaemia or iron deficiency is untreated, it can lead to other health problems, including:

1. Rapid or Irregular Heartbeat

When you’re anaemic, your heart has to pump more blood to make up for the small amount of oxygen that can lead to an irregular heartbeat. In severe cases, it can lead to heart failure or an enlarged heart.

2. Pregnancy Complications

In severe cases of iron deficiency, a child may be born prematurely or with a low birth weight.

Most pregnant women take iron supplements as part of their prenatal care to prevent this from happening.

3. Delayed Growth in Infants and Children

Infants and children who are severely deficient in iron may experience a delay in their growth and development.

They may also be more likely to experience infections.

Chapter 6: How Is Iron-Deficiency Anaemia Treated?

1. Iron Supplements

Iron tablets can help restore iron levels in your body.

If possible, you should take iron pills on an empty stomach, which helps the body absorb them better.

If they upset your stomach, you can take them with meals.

You may need to take the supplements for several months.

Iron supplements may cause constipation or stools that are black in colour.

A non-constipating form of iron is iron glycinate.

2. Diet

Diets high that include the following foods can help treat or prevent iron deficiency:

  • red meat
  • dark green, leafy vegetables
  • dried fruits
  • nuts

Additionally, vitamin C helps your body absorb iron.

If you’re taking iron tablets, I suggest taking the pills along with a source of vitamin C, like a glass of orange juice or citrus fruit.

Treating the Underlying Cause of Iron Deficency

If you have tried supplementing, modifying your diet and your doctor has ruled out any serious causes of anaemia such as internal bleeding, then you more than likely have an absorption problem.

In my clinical experience, the most common causes of poor iron absorption include:

Did I Miss Anything?

Now I would like to hear from you.

Whisch part of the guide did you find most useful?

Or maybe I did not mention a question regarding rion deficiency anaemia.

Either way, let me know by leaving a comment below right now.


This article is not intended to provide medical advice, diagnosis or treatment.