Carnivore Blood Tests: Which Numbers Move, Which Ones Lie, And What To Say To Your GP

Your printout is going to be read against a reference range built from people who eat toast.

That is the whole problem with a carnivore blood test, and not one part of it is about your health.

The labs are accurate. The assays are good. The reference ranges are honest descriptions of the population they were drawn from, which is a nation that has eaten carbohydrate at every meal since rationing ended. You walked out of that population. Nobody has told the printout. So two or three of your numbers drift past a line that was never drawn around you, they arrive on a screen that colours them red, and the person reading the screen has seven minutes and forty other results to get through before lunch.

Read this before the appointment. It covers the seven panels a GP actually runs, which numbers carnivore moves and which way, the three reds that mean nothing, the two that are worth a second look, how to turn up to the needle so the printout describes you instead of your training week, and the seven sentences to say across the desk.

It will not read your results. Nobody can do that from a web page, and anybody offering to is selling something.

One line before the panels, the same one at the top of the kidneys piece. Everything here is written for people who are well. If you already have a diagnosed condition on any of these panels you have a clinician for it, and this article does not replace them. It makes you harder to rush.

What the NHS actually runs

Ask for “bloods” and you get some subset of six: a full blood count, urea and electrolytes, liver function, a lipid profile, HbA1c, thyroid function. Ferritin, B12, folate and vitamin D get added when somebody can think of a reason. Between 40 and 74 in England you are entitled to an NHS Health Check every five years, which is the lipids and a diabetes screen with a blood pressure cuff attached.

The units will confuse you before the numbers do, and this is where British readers get frightened by American content. The NHS reports cholesterol and glucose in mmol/L, HbA1c in mmol/mol, creatinine in umol/L, CRP in mg/L. American carnivore forums report cholesterol in mg/dL and HbA1c as a percentage. A total cholesterol of 7.0 here is 270 there. A fasting glucose of 5.5 here is 99 there. If a number on the internet looks catastrophic, check the units before you check your pulse.

Since 31 October 2023, GP practices in England have been contractually obliged to show you your new results online, in the NHS App, by default. Nobody has to ring the surgery any more and be told “normal, no action” by a receptionist reading a screen upside down. The numbers are there, with the reference ranges beside them, usually before your GP has looked at them. Go and read them. Everything below assumes you have.

Lipids

This is the panel that starts the fight, so it gets the shortest section on the page, because the fight already has its own article.

The panel is total cholesterol, HDL, non-HDL, LDL and triglycerides. The NHS stopped asking you to fast for it in 2014 and has not changed its mind since, which matters mainly because a non-fasting triglyceride reads higher than the same person’s would after twelve hours without food. ESTABLISHED.

What carnivore does to it: triglycerides fall, HDL rises, and LDL does one of two things. In most people it wanders up a bit. In lean, active people it can climb a very long way, and the leaner the person, the further it goes. Ketogenic dieters have been measured showing LDL rising in inverse proportion to body mass index, which is a sentence worth reading twice, because it means the number goes furthest in exactly the people the number was invented to worry about. The pattern has a name now, the lean mass hyper-responder. ESTABLISHED as a pattern. What it does to the arteries of the people who show it is the live question in the field, and DISPUTED is the honest stamp.

What your GP does with it: feeds it into QRISK3, which takes your age, sex, blood pressure, smoking status, the cholesterol-to-HDL ratio and a dozen other things and produces a ten-year risk of a heart attack or stroke. Ten per cent or more and you are offered twenty milligrams of atorvastatin. The same 2023 guideline also says the offer should not be ruled out below ten per cent if you would like one anyway, which is a threshold with a door in both walls. The conversation you want is about the inputs to the calculator rather than the one number that frightened everybody, and the cholesterol article has the inputs.

Glucose and metabolic

The panel is HbA1c, fasting glucose where anybody still bothers, and fasting insulin if you ask and they agree, which they will not.

HbA1c is the number that diagnoses diabetes in this country. 48 mmol/mol or above is diabetes. 42 to 47 is what they call pre-diabetes, a condition invented by moving a line. ESTABLISHED, because it is a definition rather than a finding.

What carnivore does to it depends entirely on where you started. For a type 2 diabetic it falls, and it falls hard enough to change the diagnosis. In the biggest trial of carbohydrate restriction ever run on type 2 diabetes, the intervention arm’s average HbA1c went from 7.6 per cent to 6.3 in a year, and six in ten of the people who finished the year no longer met the definition of a diabetic. Insulin prescriptions were reduced or stopped in ninety-four per cent of the people on it. ESTABLISHED. That is the most important blood-test fact on this page, and it is the one a newly diagnosed reader has never once been told in a surgery.

For someone who was never diabetic, HbA1c sits roughly where it sat, or drifts down a point, and then something odd can happen to the fasting glucose.

It goes up. Not into a diagnosis. Up. 5.0 becomes 5.6, and everybody panics. The body has stopped receiving carbohydrate and has become stingy with the glucose it makes itself. Muscle that has switched over to running on fat stops pulling glucose out of the blood with any enthusiasm, because the brain is a more deserving customer. Physiologists have had a name for this for decades, glucose sparing, and it is the opposite of the pathological version on every axis that counts: it comes with low insulin rather than high, and it unwinds within days of eating a potato. ESTABLISHED as a phenomenon. Whether a slightly raised fasting glucose in a low-insulin body carries any of the risk the same figure carries in a high-insulin body is the thing nobody has settled, and DISPUTED is what you say out loud in the room.

One further wrinkle that will not come up at the surgery. HbA1c measures how much glucose has stuck to your red blood cells over their lifetime, so the answer depends on how long the cells live. Longer-lived red cells read higher for the same average glucose, and there is a suggestion in the literature that years of low-carbohydrate eating stretches red cell life out. THEORY. The practical consequence is small: a carnivore HbA1c of 38 and one of 40 are the same news.

The full metabolic piece, with fasting insulin and the case for demanding it, lands after the autumn.

Liver

The panel is ALT, AST, ALP, GGT, bilirubin and albumin. Two of them move on carnivore, for two entirely different reasons, and one of those reasons will get you a phone call on a Thursday afternoon.

The good one first. ALT is the liver’s own enzyme, and a raised ALT in a heavy person is nearly always fat in the liver. Carbohydrate restriction empties a fatty liver faster than anything else anyone has tried on it. Eighteen people with fatty liver, thirteen of them women, were put on two weeks of either carbohydrate restriction or calorie restriction and lost the same four kilos either way. The carbohydrate group’s liver fat fell by 55 per cent. The calorie group’s fell by 28. Same weight off, twice the liver emptied. ESTABLISHED. If your ALT was high before you started and you have since lost weight, expect it to come down, and expect your GP to be pleased about it without being entirely sure why.

Now the phone call. AST and ALT do not only live in the liver. They live in muscle, and muscle that has been worked hard leaks them into the blood for days afterwards. Fifteen healthy men who were not used to lifting did one hour of weight training. Their AST and ALT were still significantly raised seven days later, high enough that a routine panel would have flagged every one of them for liver disease. Their bilirubin, ALP and GGT never moved at all. ESTABLISHED.

So: you lift. You eat enough protein to build the muscle that leaks. You give blood on a Tuesday morning after a heavy Saturday, and the printout says liver. There is nothing whatsoever wrong with your liver. The tell is sitting right there on the same page, because GGT, the enzyme that actually lives in the bile ducts and goes up with alcohol and fatty liver, is entirely unbothered while ALT and AST are through the roof. Your GP knows this pattern perfectly well. They see it in rugby players. They just need telling that they are looking at one.

Kidney

Creatinine, eGFR, urea, sodium, potassium, and urate when somebody remembers. This is the panel most likely to produce a frightened phone call about nothing at all, which is why it has its own article, and why that article is the one to read before you go.

The short version. Creatine in meat turns into creatinine in the pan, you absorb it, and your creatinine goes up. You also carry more muscle than the formula assumes. eGFR is calculated backwards from creatinine, so it falls. Eighty people were given a single cooked meat meal, and six of the sixteen with stage 3a kidney disease were reclassified as stage 3b on kidneys that had not changed in any respect since breakfast. The effect vanished completely after twelve hours of fasting. ESTABLISHED. Urea rises because protein is nitrogen and urea is the exit. ESTABLISHED, and boring in a working kidney. Cystatin C is the alternative estimate that does not care what you ate or what you lift, and it is the test to ask about the moment the eGFR conversation turns serious.

Urate goes up in the first few months and then settles. For most people that is a figure on a page. For a minority it is a toe at three in the morning, and the gout article is where that lives, including the one instruction that matters if you are already on allopurinol, which is that you keep taking it.

Thyroid

The NHS tests TSH first. If TSH is normal, that is usually the whole appointment. Free T4 gets added when TSH is off. Free T3 is barely measured in primary care at all. That sequence matters, because the only thyroid number carnivore reliably moves is the one nobody measures.

T3 falls on very low carbohydrate intakes. Six healthy men were fed three diets of identical calories and identical protein, differing only in carbohydrate, at 85 per cent, 44 per cent and 2 per cent of energy. On the 2 per cent diet their T3 dropped, their reverse T3 and free T4 both rose, and their TSH did not move a millimetre. Their resting energy expenditure did not change either, which is the detail that matters, because a genuinely underactive thyroid is a body burning less. ESTABLISHED as a finding. Whether a lower T3 alongside a normal TSH, in a woman who is warm, sleeping well and losing fat, is a problem or an efficiency is DISPUTED. The body converts T4 into T3 according to what fuel is arriving and in what form, and a fat-fuelled body appears to need less of it to do the same work. That is the most defensible reading available, and it is still a reading.

What this means in the room: your TSH will almost certainly be normal, your GP will almost certainly say your thyroid is fine, and they will almost certainly be right. If you are cold, flat and exhausted on a normal TSH, that is a real conversation, and free T4 and free T3 are the numbers to ask for before anyone reaches for a prescription pad.

Blood cells

The full blood count: haemoglobin, red cells, white cells, platelets, with ferritin, B12 and folate bolted on when somebody has a reason.

For a menstruating woman this is the panel carnivore improves fastest and by the widest margin, and almost nobody in this space writes about it. Iron deficiency is the most common nutritional deficiency on earth and it falls overwhelmingly on women of reproductive age. The iron in red meat is haem iron, absorbed at somewhere between 15 and 35 per cent, against 2 to 20 per cent for the iron in spinach or a fortified cereal, and it arrives with B12 attached, which no plant carries at all. ESTABLISHED, all of it, for as long as nutrition has been a subject. A woman with a ferritin of 11 who has spent a decade being told she is tired because she is a busy mother, and that 11 is the low end of normal, tends to have a very different-looking count six months into eating steak.

For everybody else, B12 and ferritin will read high-normal and sometimes over the line. A high B12 on a diet made entirely of the only foods that contain B12 is arithmetic rather than a finding. A high ferritin earns one more look, because ferritin doubles as an inflammation marker, and a high ferritin next to a high CRP is a different conversation from a high ferritin next to a low one. Say that out loud and ask for the CRP alongside it.

Haemoglobin and red cell count can creep up, because the raw materials are there. Top of the range is top of the range. Above the range for the first time is worth asking about plainly, because a handful of things other than dinner do that.

Nutrients and electrolytes

Sodium, potassium, calcium, magnesium, and vitamin D when the NHS can be persuaded, which it usually cannot.

The electrolytes are a transition story rather than a diet story. In the first weeks without carbohydrate, insulin falls, the kidneys stop hoarding sodium, and the water goes with it. That is the headache, the calf cramp and the thumping heart that the internet has branded keto flu. It is a body recalibrating its sodium handling after decades of being told to hold on to everything, and it passes. Aldosterone goes up, the kidney tightens its grip, and the whole business resolves itself on a timescale of a fortnight or so without anybody reaching for the cellar. Not one animal that walks miles to a salt lick is a carnivore. They are all herbivores, on a diet with no sodium in it, doing something a lion has never once needed to do.

The blood test reads normal throughout all of that, because the body defends blood sodium ahead of nearly everything else it owns, which is precisely why you can feel dreadful with a perfectly ordinary sodium result on the page. The number is not measuring how you feel. It never was.

Magnesium gets a paragraph because it is the number people chase and the number the test cannot see. Under one per cent of the body’s magnesium is in the blood, that fraction is defended hard, and a normal serum magnesium says almost nothing about the stores sitting in muscle and bone. ESTABLISHED, and it is why a normal magnesium result and a nightly cramp can both be true at once without anyone lying.

Vitamin D does not change because you ate beef. It changes because you went outside. If you are paying for one private test it is a reasonable one to pay for, and the cure is daylight, the time of year, and a bottle in January.

Inflammation

CRP is the one-number inflammation marker and it belongs on the form if you can get it on the form. It falls with fat loss and it falls when the things that were inflaming you leave the plate. It also spikes after hard training and after any infection going, so a CRP drawn three days after a cold and two days after a heavy session is a faithful report on the cold and the session. Same rule as the liver enzymes: the printout is describing your week.

How to turn up to the blood draw

Most of the red on a carnivore printout was put there by the seven days before the needle rather than by the diet. Control the week and most of it disappears.

• No hard training for 72 hours. The one that matters most and the one nobody does.
• Twelve hours without food. Clears the cooked-meat creatinine entirely.
• No alcohol for three days. GGT and triglycerides.
• Water as normal. Dehydration concentrates everything.
• Morning, same lab, same conditions, every single time.

The NHS stopped requiring a fast for lipids years ago, so fast anyway, because the reason to fast was never the lipids. It was the creatinine, and the study that proved it used one meal.

A single number is worth very little. A trend is worth everything, and a trend needs the conditions held still, which is why the fifth line above is doing more work than the first four.

And give it three months before you judge anything at all. Red cells live about 120 days, so an HbA1c drawn in March is partly a report on Christmas. Lipids take weeks to settle and LDL can still be climbing at six months in a lean person. Urate spikes early and comes back down. A panel drawn at week three is a photograph of a body halfway through moving house.

What to ask your GP

Seven sentences. Write them on something. The appointment is short and the screen is red.

“Can I see the numbers and the ranges rather than the flags.” You can already see them in the app. Saying it out loud changes the temperature of the appointment.

“What is my QRISK3 score, and which inputs are driving it.” The calculator decides what you get offered. The cholesterol figure on its own decides nothing.

“Can we read the triglycerides and HDL together as a ratio.” The best-looking part of a carnivore lipid panel, and the part least likely to be mentioned by anybody.

“I lift and I eat a lot of protein. Would cystatin C estimate my kidney function better than creatinine.” The kidneys article has the whole case.

“That blood was taken two days after a heavy session. Could the liver enzymes be muscle, given the GGT is normal.” The rugby player pattern, handed over politely.

“My TSH is normal. If we are looking at the thyroid at all, can we see free T4 and free T3.” Only worth saying if there is a symptom to chase.

“Can we repeat this in three months under the same conditions.” The sentence that turns a frightening number into a data point.

What this page will not do

It will not read your results. Not in the comments, not by email, not for money. A number with no person attached to it is noise, and the person attached to yours is your GP, who has your history, your blood pressure, your family, your examination and your face in front of them, none of which is available here. What this page does is make sure that when you sit down opposite them, you know which panels exist, which numbers your diet moved, which ones your Saturday moved, and what to say about the difference.

Turn up knowing that, and the appointment stops being something that happens to you.

The three deep pieces, for when one panel swallows the whole appointment: cholesterol, kidneys, gout.

The panels, decoded

Carnivore Blood Test Questions

Do I need to fast for a carnivore blood test on the NHS?

Not for lipids since 2014. Fast twelve hours anyway, because cooked meat raises creatinine and twelve hours clears it.

Why is my cholesterol high on carnivore?

Lean, active people often see LDL climb, and the leaner they are the further it goes. What it means is contested. QRISK3 and its inputs decide what you get offered.

Why are my liver enzymes raised on carnivore?

Weight training raises AST and ALT for at least a week. Raised ALT and AST with a normal GGT after a heavy session is the muscle pattern, not the liver.

Why has my eGFR dropped on carnivore?

Cooked meat and muscle mass both raise creatinine, and eGFR is calculated from creatinine. Cystatin C is the estimate that does not care.

Is a low T3 on carnivore hypothyroidism?

Not with a normal TSH, normal energy expenditure and no symptoms. T3 falls on low-carbohydrate diets by a known mechanism whose meaning is disputed.

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