In the last installment of this series, we worked through the details of the Complete Blood Count. As discussed, the CBC panel reveals how many of the different types blood cells are circulating through your veins. 

However, there’s more in your bloodstream than just red and white blood cells. Your blood is also the transportation system for thousands of different molecules which have their own unique tasks. 

Think of a busy subway train in the morning. On that train, you’d see people with all kinds of professions: bankers, baristas, teachers, construction workers, and so on. When the train stopped, all the workers would spill out and go to their various jobs, but they all need to ride the same train. So it is with the bloodstream, where vitamins, minerals, sugars, proteins, and all kinds of specialized molecules float in the plasma, stopping at different stations around your body to perform their essential tasks.

When a physician wants to see what’s going on inside your body, they can take a blood sample and check how many of these different worker molecules are present. If there are too few or too many of a certain molecule, it’s a good clue about the nature of any underlying problems. The test to find these specialized molecules is the Comprehensive Metabolic Panel (CMP).

The results of the CMP are even more confusing than the CBC. It’s easy enough to understand what a red blood cell count is, but phosphorus? Bilirubin? These sound like the terms of a medieval apothecary diagnosing your humours, not a modern medical test. What does it all mean?

Today we’re going to walk you through the ins and outs of this confusing blood test in simple, clear language, and give you a sense of what doctors are looking for when your results come in. We'll start with the star of the show, fasting glucose level.

Glucose (fasting reference interval)

How do you power a jet? You put in jet-fuel. How do you launch a rocket? You put in rocket-fuel. How do you power an oxygen-breathing plant or animal? You put in life-fuel. Glucose is life-fuel. Glucose is a chemical arrangement of carbon, hydrogen, and oxygen that packs a lot of energy into a stable package.

Glucose is a saccharide, just like sucrose (sugar) and fructose (plant sugar). All the “-oses” share a similar molecular blueprint, with carbon forming a long “spine” where hydrogen and oxygen can easily be pulled off.  This is why glucose goes by the street name “blood sugar.” 

When a plant or animal needs energy, cells open up and let glucose from the bloodstream enter the cell walls. The glucose is then broken apart (metabolized), releasing their stored energy that allows the cell to complete its functions.

In short, glucose is really important, and that's why it's the top line item on your CMP results.

Aafter eating (especially something sweet), glucose levels are elevated in the blood for several hours. Your doctor doesn’t want to be wondering if high glucose is from an internal problem or a jelly donut, which is why you need to have the CMP taken after at least 8 hours of fasting. 8 hours ensures your blood glucose is at background levels and not spiked from a food input. Hence, the result you see is your fasting glucose level.

If you have low glucose

We all have passing moments when our blood sugar drops. This will make you feel lightheaded and lethargic, but the body can usually rally, with the liver pumping out stored glucose to rebalance your energy levels. However, if you’re consistently showing low glucose on blood tests (hypoglycemia), it’s usually for following reasons:

• Adverse reactions to medications are the most common reason for low blood glucose. For example, quinine, an anti-malarial medicine, can lead to low glucose levels. Many medicines have this side effect, especially if the kidneys aren't clearing the medicine quickly enough.

• Starvation and malnourishment will lower also glucose levels, most often seen in the developed world in cases of anorexia.

• If the pancreas is producing too much insulin, your blood glucose will be too low. This is a rare disorder caused by tumors on the pancreas.

If you have high glucose

This is called hyperglycemia, and is a much more likely result than low glucose. High glucose is related to the global epidemic of diabetes.

Since glucose is so key to cellular metabolism, the body has evolved a suite of complementary hormones to regulate how much sugar is in your blood. The most important of these is insulin, which floats through your system, opening up cellular doors to allow glucose to enter the cells. In type 1 diabetes, the pancreas doesn’t produce enough insulin for genetic reasons. In type 2 diabetes, the body has been exposed to so much insulin (often due to a high sugar diet) that the cells have developed insulin resistance and won’t open properly. High blood glucose usually indicates that something is going wrong with normal insulin function.

By far the main cause of high glucose levels in people’s CMP is due insulin-related problems. The metabolic panel is extremely useful to catch pre-diabetes and early diabetes. In the early stages, the patient won’t have any symptoms, but the high glucose will illuminate what’s going on, and preventative steps can be taken. If diabetes can be headed off at the pass before medication is required, patient prognosis and quality of life rises significantly. This is why a doctor is very interested in your glucose levels.

Beyond diabetes, there are other causes for high glucose. These include the following:

• Even without full-blown diabetic insulin resistance, obesity and a sedentary lifestyle will result in higher glucose levels. When you consistently have too much sugar in your blood you’ll feel fatigued, lightheaded, and headachy. Healthy blood glucose is the cornerstone of feeling well.

But glucose is just the tip of the iceberg in terms of what the complete metabolic panel is looking at. Let's move on to the wacky electron loving elements that make up your electrolytes.

Electrolytes (sodium, potassium, chloride, bicarbonate, and calcium)

The standard CMP will usually list these together, because they’re all different salts, and all share a similar function in the body. Let’s talk about what that function is.

When you see one of Boston Dynamics' robots move an arm or lift a leg, you know that what's happening is that an electrical impulse is traveling from the processor to the servo in the limb. You could open up the robot and trace that little wire from the motor all the way back to the motherboard.

Organic life doesn’t have the ability to run metal wires from the brain to the different body parts. It has the challenge of sending signals through a bunch of water filled tubes.

Wiggle your left big toe right now. Isn’t it amazing that your brain can get the message all the way to the other end of your body, even though it’s not connected by anything but soggy cells and nerves?

Electrolytes are what make signal transfer through water possible. When placed in water, these molecules dissolve into negative and positive charged ions. When there are enough of these ions, a signal can successfully pass through the liquid.

These positive and negative ions also maintain cell integrity, as osmosis ensures that whichever side of the cell has a positive charge is where water will flow. If you were to suddenly remove all the salts from your body, your cells would instantly burst apart or shrivel up as this balance would be destroyed. This is why your physician is interested in seeing how many electrolytes are in your blood. They’re very important!

If you have low electrolytes:

Low sodium, potassium, chloride or bicarbonate can be caused by a number of issues, some easy to solve, others very serious:

If you have high electrolytes:

The most common cause of high electrolytes is dehydration. This can happen either through not drinking enough fluids, or because diarrhea or vomiting has quickly reduced your water content. When there’s not enough water in your system, electrolytes will stop ionizing and electrical balance is thrown off.

When someone dies from thirst, it’s usually because their brain can no longer communicate with the heart, the heart stops pumping, oxygen stops moving, and the brain cells die. Dying from thirst isn't a water problem, but an electrical problem!

A poor diet high in sodium and processed food will lead to elevated electrolyte levels. This stresses the liver and kidneys, which have to put in overtime to filter the salts and maintain correct ion balance. As the liver and kidneys are worn out, electrolyte levels will gradually creep up year by year. If your blood test shows a one-off high electrolyte reading, your doctor will probably chalk it up to chance. But if year after year electrolytes are rising, it's an early clue that something's up!

Proteins (albumin, bilirubin)

The next set of molecules that the CMP explores is two proteins floating around your bloodstream.

You might think of proteins as having to do with making muscle, but a protein is any amino acid structure which performs a function in your body. As an analogy, look around at your kitchen appliances. They’re all made of metal and plastic, but depending on how that metal and plastic is structured, it can cool food down (refrigerator), heat it up (microwave), chop it into pieces (blender), or combine foods together (mixer). Proteins work the same way. Using just 20 amino acid building blocks, 20,000 different protein structures have evolved for all the many small tasks that are required to keep you alive and functioning. Some of those proteins are found in the blood, and are an important clue to the state of your health and wellness.

The CMP has a method of chemical analysis to tease out how many proteins are in your blood, which is what gives you the total protein reading. 

This total protein is further broken down into the two most important blood proteins, albumin and bilirubin. 

Albumin is a key housekeeping protein. It circulates through your system and helps usher hormones, vitamins, medicine, fats, minerals and various other molecules to the right place at the right time. You can think of it was the delivery van of the blood. It also regulates osmotic pressure in the blood vessels, making sure that your arteries and veins don’t leak fluid into the rest of the body.

Bilirubin protein is what decommissions blood cells, especially red blood cells, that have come to the end of their life. It takes apart the cells, tidies up the area, and then hitches a ride with albumin to reach the kidneys and dump the waste. This is why albumin and bilirubin are closely linked in function, and show up together in your total protein results.

The byproduct of red blood cell cleanup is a yellowish substance. When your cells take a lot of damage in one spot (like getting punched hard in the arm), the bilirubin comes and takes away the damaged cells, leaving a brown yellow smudge behind which we know as a bruise. When bilirubin is overactive and decommissioning way too many red blood cells, the entire skin can turn yellow, which is what causes jaundice.

In general, if total proteins are low, it indicates a problem at the protein factory — the liver. If total proteins are high, it indicates a problem at the protein garbage dump — the kidneys. Any diseases which touch on these two organs will show up in out-of-range albumin and bilirubin levels.

As you can see, the CMP is able to infer a lot of information about the liver and kidneys. Now that you have a sense of this relationship, we can cover the final, most confusing elements of the CMP.

Kidney Fuction (BUN, Creatinine, and eGFR [CKD-EPI])

Imagine a city with no water treatment plant. When you turned on your faucet, you’d get a mixture of whatever had gone into the sewers that day: medical waste, chemicals, feces, etc… Pretty gross to think about right? 

The kidneys are the water treatment plants of the body. They filter, break down, and recycle material day and night. Healthy kidney function is critical for well-being.

There are three particular blood components which tell your doctor how well your kidneys are doing in this essential work. On your blood test results these are very unhelpfully named with confusing acronyms.

Let’s break them down.

BUN (blood urea nitrogen)

Your body is constantly in the process of breaking down cellular structures and rebuilding new ones. Every day, about 1% of your cells are replaced in this way. One of the most common byproducts of cellular break down is the simple molecule ammonia. 

Ammonia’s molecular structure leaves a big, juicy nitrogen atom sticking out into the bloodstream. As it travels around your body, this nitrogen attracts carbon, hydrogen and oxygen, resulting in a strongly bonded molecule called urea. The kidneys have evolved to be adept at capturing and filtering out urea, which leaves the body as urine. When your urine has a strong ammonia smell, it’s an indication that high amounts of urea have collected in your bladder and are now leaving the body. (Incidentally, the yellow color of urine is a byproduct of the yellowish bilirubin byproduct discussed above.)

The CMP measures the amount of urea-bound nitrogen in the blood, hence the name blood urea nitrogen (BUN). 

If your BUN is high, it can indicate that the kidneys aren’t doing their job and letting urea pass through the body without filtration.

If someone is on a high protein diet this will also increase BUN, because the liver is breaking down so much animal protein that the kidneys can’t keep up with the ammonia being sloughed off from the liver breaking down the amino acids.

Creatinine 

You’ve probably heard of the bodybuilding supplement creatine. This molecule is produced in the liver and plays a role in how much work a muscle can do before it fatigues. People wanting to make more muscle will take supplemental creatine to push harder during their workouts and break up more muscle tissue. This tissue will heal bigger and stronger so they can bulk up.

Creatinine is the leftover byproduct of creatine, and is sent into the bloodstream as you flex and move your muscles. It's the waste product of muscular exertion.

The useful thing about creatinine is that it stays in the blood at a steady-state concentration. A healthy body will almost always have the same amount of creatinine in the blood (accounting for body size and sex). This makes it a great benchmark for how well the kidneys are functioning (much more so than BUN which can be affected by hydration and diet).

Understanding creatinine allows you to unlock what’s going on behind the next hellish acronym on the metabolic panel.

eGFR (CKD-EPI)

The eGFR stands for estimated Globular Filtration Rate. This takes the raw amount of creatinine and runs it through an equation based on your race and sex. Which equation you ask? Why, the equation produced by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI). 

Essentially this gives your doctor a more usable number than raw creatine stats (taking into account genetic factors), and estimates how well your kidney is filtering waste, using the “standard candle” of blood creatinine.

You don’t want high BUN or creatinine levels in your blood. You DO want a high eGFR. That means your kidneys are filtering efficiently.

Causes of kidney malfunction and bad blood results are varied, but the most common are no surprise:

• Diabetes damages the small, delicate blood vessels of the kidney, as glucose-rich blood is having to be filtered at a much higher rate than normal. This wears out the kidneys quickly.

• High blood pressure also stresses these filters, causing a slow loss of kidney function year over year.

The message is clear. Eat right, exercise, and don’t smoke. Your kidneys have enough to do without added stress!

This leads us to the final set of results on the CMP, which come from the other end of the kidney-liver relationship.

Liver Function (ALP, ALT, and AST)

Oh no! Another set of impenetrable acronyms! Fortunately these share similar functions and are relatively easy to understand. All three are enzymes the liver uses to break down food into useful building blocks for the body.

If you ask someone what the most important organs in the body are, they'll usually mention the heavy-hitters, "heart, lungs, brain, maybe the stomach." Everyone forgets the humble liver, but it's one of the coolest, most underrated parts of your body.

Imagine if you went to a restaurant and ordered pasta, but instead of a completed dish, the waiter brought you a bag of flour, some raw eggs, and a cup of water. You'd say "Are you joking? I can't do anything with this! It's not edible!" Just having the raw materials of food isn't enough, you need a kitchen to assemble and bake the ingredients into a palatable, digestible dish. This is what the liver does for you. It takes all the raw ingredients that you ate, strips them down into component molecules, recombines them into what your body needs, then ships them out to your organs, bones, and muscles. The kitchen staff that it uses is a ragtag group of enzymes which are specially evolved to take apart specific combinations of food.

The CMP looks for three of these enzymes in particular.

Alkaline phosphatase (ALP)

This is the enzyme which breaks phosphate-bearing proteins in your food.

ALT is the enzyme which strips down alanine-bearing molecules into amino acid building blocks.

AST is the enzyme which converts aspartate and other proteins into usable amino acids.

What does high ALP, ALT, or AST mean?

Your doctor doesn’t want to see high levels of these enzymes in your blood panel. If they do, it essentially means your liver structure is compromised somewhere, and “leaking” enzymes into the bloodstream. The different enzymes give your doctor clues about where the problem may be. For example, high ALT alone indicates problems with liver tissue, while high ALT in combination with high ALP points towards a clogged bile duct.

The list of illnesses which can damage the liver is long, but the most common sources are familiar to you.

• Diabetes rears its head again, as insulin resistance forces the liver to work far outside its preferred glucose range. This creates a lot of stress on the liver tissue, which leads to a downward spiral as a less healthy liver is able to produce less and less healthy building materials for the body to recover and rebuild with.

• Excess alcohol consumption greatly stresses the liver and leads to scarring (cirrhosis).

• Hepatitis A, B, and C are all infections which inflame and scar the liver, reducing normal function.

• A variety of cancers and genetic diseases are centered around the liver and reduce liver function.

Checking the blood for higher than expected levels of ALP, ALT, and AST is the first clue that something is amiss in the liver, long before more serious symptoms show themselves, which is why your doctor wants to see those stats on your metabolic panel!

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This was a lot of information to cover, and it’s ok if you didn’t internalize it all. The goal of these articles is to show you that these esoteric numbers are all just ways of measuring the very real molecules floating around your blood. By itself, any given data point could be caused by a large number of things. But when taken together, your doctor can start to hone in on exactly what’s going on inside the otherwise black box that is your body.

Imagine a child’s connect-the-dots picture. If there are only a few dots on the page, it’s impossible to figure out what the image is. But the more dots you add, the clearer the picture becomes. The granular data of the comprehensive metabolic panel gives your physicians a lot of dots to work with. And of course, as the outlines of a problem begin to form, even more precise tests can be ordered.

As you can tell, the CMP will quickly throw up red flags if anything's amiss with your blood sugar, liver, or kidney function. Combined with the complete blood count (part 1) and lipid panel (which we’ll cover in part 3), your blood lays out a detailed status report about the inner workings of your body, and it often gives you years of advanced warning to address small problems before they become major health crises. Help your physician connect the dots by getting your blood checked at least once a year!

We'll wrap up this series by diving into the fascinating world of the lipid panel. Stay tuned!

Patrick Reynolds // Kenzai Founder