B12, folate and CRP: the extra markers on your panel.

Vitamin B12 and folate are the two vitamins behind healthy red blood cells and healthy nerves. CRP is a general marker of inflammation. They sit on fatigue, preconception and postpartum panels because low B12 or folate is a common and correctable cause of exhaustion, and CRP tells your doctor whether inflammation is in the picture at all.

Why these three appear on women's panels

Iron and thyroid get most of the attention when someone is tired, and rightly so. But a panel that stops there misses two other common causes of the same symptoms, and gives your doctor no way of knowing whether an inflammatory process is running in the background.

There are five groups of women in whom B12 and folate are especially worth checking:

• Anyone eating little or no meat, dairy or eggs. B12 comes almost entirely from animal foods, so vegetarian and vegan diets are a common reason for a low level in an otherwise well person.
• Anyone planning a pregnancy. Folate status before conception matters for the developing baby, and B12 works alongside folate.
• Anyone in the year after a baby. Pregnancy and breastfeeding draw on both, and the symptoms of a low level look exactly like new-parent tiredness.
• Anyone over about 50, or with a gut condition or gut surgery. Absorption of B12 falls with age and with anything that affects the stomach or small bowel.
• Anyone with an autoimmune condition, particularly autoimmune thyroid disease. Pernicious anaemia, in which the immune system stops the stomach making the protein needed to absorb B12, is the commonest cause of a clinically significant B12 deficiency and is more common in women.

CRP is different. It is not a vitamin and not something you can be deficient in. It is a protein the liver releases when there is inflammation anywhere in the body, and it earns its place on a fatigue panel as a "is something else going on" check.

B12 and folate: what the numbers mean

Both vitamins are needed to build red blood cells. When either runs low, the bone marrow produces fewer, larger cells, which shows up on a full blood count as a raised mean cell volume before it ever shows up as anaemia. That is why these markers are read alongside the full blood count rather than on their own.

Marker	Typical adult range	What it usually means
Vitamin B12 (serum)	About 150 to 700 pmol/L	Below the lower limit is low. Results in the bottom part of the range can still be symptomatic, so borderline levels are often rechecked with a second marker.
Active B12 (holotranscobalamin)	Reported where available	Measures the fraction your cells can actually use. Some laboratories use it instead of, or after, a serum B12.
Folate (serum)	Above about 10 nmol/L	Reflects recent intake, so it moves quickly with diet. Red cell folate reflects the last few months and is sometimes used instead.
Homocysteine or methylmalonic acid	Laboratory specific	Homocysteine rises when either B12 or folate is lacking at cell level. Methylmalonic acid rises only with B12 deficiency, which is why it helps sort out a borderline B12.
Mean cell volume (on the full blood count)	About 80 to 100 fL	A raised volume with a low B12 or folate is the classic pattern. It can be normal even when a vitamin is low.

Ranges vary by laboratory; your report shows the range your lab uses. Typical ranges on this page are drawn from Pathology Tests Explained (RCPA) and the sources listed below.

The symptoms of a low B12 or folate overlap heavily with low iron and an under-active thyroid, which is exactly why they are tested together. They include:

• Tiredness that rest does not fix, and breathlessness on stairs.
• Pale skin, or a smooth, sore tongue and mouth ulcers.
• Pins and needles, numbness or an odd burning feeling in the hands and feet.
• Poor balance, or feeling unsteady in the dark.
• Memory lapses, poor concentration and low mood.
• Irritability, and in some people palpitations.

The nerve symptoms matter. Nerve changes from a long-standing low B12 can persist if a low level goes unrecognised for years, which is the main reason doctors like to see the number rather than assume.

A low B12 in someone eating a normal diet raises the question of pernicious anaemia, an autoimmune condition checked with intrinsic factor antibodies, and of long-term medicines that reduce B12 absorption, including acid-suppressing medicines and one commonly used diabetes medicine. Your doctor decides which of those checks are worth doing.

The pregnancy link is folate. NHMRC guidance is that folate status before conception and in the first weeks of pregnancy is important for the baby's developing spine and brain, and your GP or midwife will tell you what you need and when to start. A preconception panel measures where you are starting from. Whatever the number, Australian guidance is that everyone planning a pregnancy takes folic acid daily from at least a month before conception, so the test is not a substitute for that; what you take and for how long is a conversation with your doctor or midwife, not something to work out from a number alone.

CRP: what an inflammation marker can and cannot tell you

C-reactive protein rises within hours of inflammation starting and falls again just as quickly once it settles. In most Australian laboratories a result under about 5 mg/L is reported as normal, although some use a cut-off of 3, 8 or 10 mg/L, and your report shows the one your laboratory uses.

Here is the honest limitation: CRP is completely non-specific. It tells your doctor that inflammation is present, not where it is or why. A common cold, a recent dental infection, a flare of an inflammatory condition, a recent injury, a hard gym session, obesity, pregnancy and the oral contraceptive pill can all lift it. That is why a mildly raised CRP in someone who feels well is usually repeated in a few weeks rather than investigated straight away.

What it is genuinely good for:

• Ruling inflammation out. A normal CRP in someone with vague, long-standing symptoms is reassuring, and it steers the search elsewhere.
• Context for other results. Ferritin rises with inflammation, so a normal-looking ferritin with a high CRP may be hiding low iron stores. Where inflammation is present, doctors treat a ferritin under about 70 ug/L as still compatible with low iron stores. Your doctor reads the two together.
• Tracking a known condition. Where a doctor is already following an inflammatory condition, the trend in CRP is more useful than any single value.

A markedly raised CRP with fever, pain or feeling very unwell is a reason to see a doctor promptly, not a reason to wait for a follow-up test. A high CRP by itself does not point to any particular condition, and it is not a screening test for anything specific.

When coeliac screening is added

Coeliac disease is worth thinking about when low iron, low B12 or low folate keeps coming back despite a reasonable diet, or when tiredness travels with bloating, loose stools, unexplained weight change or a family history. Undiagnosed coeliac disease damages the part of the small bowel where these nutrients are absorbed.

The first-line blood test is a coeliac serology panel: tissue transglutaminase antibodies together with a total immunoglobulin A level, because a small number of people do not make enough of that antibody class for the main test to be valid. A positive or equivocal result is followed by a gastroscopy and small bowel biopsy arranged by a specialist, which remains the confirming step in adults.

Two practical points. You need to be eating gluten regularly in the weeks before the blood test, or the antibodies fall and the result is unreliable. And the coeliac gene test, sometimes offered separately, works in reverse: a negative result makes coeliac disease very unlikely, while a positive one is common in the general population and confirms nothing on its own.

KnowLuna's panels do not currently include coeliac serology. If the pattern above sounds like you, that is a good conversation to have with your GP, who can order it and arrange the follow-up if it is positive.

The KnowLuna panels that include these markers

You do not order B12, folate and CRP as a stand-alone shopping list. They come bundled into the panels where they change the answer.

• The fatigue and energy check includes B12, folate and CRP alongside iron studies, full blood count, TSH, free T4, vitamin D, HbA1c, and kidney and liver function. It is $179 with your own doctor's request, or $259 with a KnowLuna doctor requesting it and explaining the results.
• The preconception check includes folate, B12, iron studies, full blood count, vitamin D, TSH, HbA1c, blood group and antibodies, and the immunity checks recommended before pregnancy.
• The postpartum recovery check covers B12 and folate with iron, thyroid function and thyroid antibodies, for the first year after a baby.

Common questions

Sources and further reading

• Pathology Tests Explained (RCPA): vitamin B12 and folate
• Pathology Tests Explained (RCPA): C-reactive protein (CRP)
• Healthdirect: vitamin B12 test
• Healthdirect: folate test
• NHMRC Nutrient Reference Values: folate
• Healthdirect: coeliac disease
• Pathology Tests Explained (RCPA): coeliac disease tests

General information only, not medical advice. If your symptoms are severe or sudden, see a doctor promptly. This page does not replace a consultation with a doctor who knows your history; read our medical disclaimer.