Blood tests: how to read blood chemistry (sugar, kidneys & more)

So you did your blood tests, there are numbers outside the range - and thanks to Google you already know far too much about a disease you don't have.

Don't worry, I'm here to explain every line in the results - so you'll know what to watch for and when you can simply relax. And today we're on part 2 of the series about blood tests - and we'll talk about chemistry, which includes blood sugar and a few other important measures.

I'm Dr. Elisheva, I'm an anesthesiologist, and here you'll get clear, direct medical information - no scare tactics and no drama - so you can make informed decisions about your health. Let's get started.

## Important rules

First, a reminder of our iron rules -

you don't look only at a number flagged in red; instead you interpret the number in the context of symptoms and additional tests.

Usually there isn't much significance to a number that's only slightly outside the range.

And when there's an abnormal result, the first thing we do is repeat the test to make sure it's real.

And this video is not a substitute for medical advice, so for very abnormal results or symptoms - please consult your treating physician.

(These rules were written in blood!)

## What is a blood chemistry panel?

Last time we talked about the count, which looks at the cells in the blood; in chemistry we test what's in the blood fluid - broadly, the test gives us information on how the body regulates water, salts, sugar, and waste. You need to fast for 8 hours from anything that isn't water before such a test. It's a test ordered when there's suspicion of diabetes or a kidney problem, but usually just as part of routine blood work.

A basic chemistry panel usually includes a few things: glucose (or sugar), electrolytes - the salts we have in the blood, kidney function, and sometimes part of liver function - but we'll talk about liver function in a separate video, because it's big enough on its own.

## Glucose (blood sugar)

Glucose is blood sugar, and it's a number that changes very significantly over the course of the day. That's why fasting is so important - because what's tested in chemistry is fasting sugar.

When you eat, the glucose level in the blood rises, and then our body secretes a hormone called insulin that's supposed to move it into the cells - and then the blood level returns to the normal range. If there's a problem in the production or function of insulin, as in diabetes, the glucose doesn't enter the cells, it stays in the blood, and then we'll see a high fasting sugar on the test.

If glucose is above 100 - that's abnormal and considered a pre-diabetic state, but you have to take into account the patient's whole clinical picture, and if the number is above 126 that's already a diagnosis of diabetes. But to make a final diagnosis we also repeat the test a second time, and we'll order a test called HbA1c, which looks at how much sugar has "stuck" to our red blood cells and gives a more comprehensive picture - not just a single fasting-sugar snapshot, but the sugar values over 3 months. If the number is above 6.5, that's a diagnosis of diabetes.

Glucose that's too low is fairly rare - even after a prolonged fast, our glucose levels are supposed to stay in the normal range, because we have another hormone whose job is to release it from our stores to keep the blood level stable. So if it's low in the blood - in the range of 50 to 70 - there are many possible causes, and often it's a one-off that doesn't repeat on a retest. If the number is below 50, it will usually come with symptoms of hypoglycemia (confusion, tremor, and sweating), and that already requires a workup.

## Electrolytes (salts)

These are the salts we have in the blood. In a routine chemistry panel we look at sodium, potassium, chloride, and calcium. Electrolytes are important for maintaining fluid balance in the body and the normal function of muscles, nerves, and the heart.

Sodium and chloride - they usually go together, so we'll talk about them together, and they're important for keeping the right amount of water in the body. If they're above normal it usually goes along with severe dehydration. When they're low, it's usually the result of diseases in which our body retains excess water, like heart failure and problems in kidney and liver function. And the numbers can also be abnormal in both directions because of medications, especially diuretics.

Potassium - especially important for the normal function of heart cells. It can be high when there's impaired kidney function, in the rare state of adrenal gland insufficiency, and if it's high while everything else is normal, that's a relatively common lab error and the test should be repeated. It can be low if we lose it through frequent vomiting, for example, or because of certain hormones in the body that are supposed to maintain its levels. And here too, of course, there are all kinds of medications that can cause a level that's too high or too low.

Calcium - a main component of bones but also found in the blood. If it's low it can be the result of vitamin D deficiency, or disorders of a gland called the parathyroid gland, which sits next to the thyroid and is responsible for maintaining blood calcium levels. High calcium can also be seen because of medications, and much more rarely in certain malignant or inflammatory diseases.

An important point about electrolytes in general - similar to sugar, we have mechanisms in the body that are supposed to keep levels stable, regardless of how much we eat. So even if you don't eat any food containing potassium, and even if you eat 10 bananas (up to a certain limit, of course), as long as these mechanisms are working properly, the levels will stay in the normal range. The dietary deficiency has to be very extreme to affect our stores and blood levels.

So remember that these numbers are not a measure of whether you eat enough potassium or calcium - they're a measure of how well these mechanisms in the body are working. That's why they're themselves a measure of normal kidney and hormonal function.

And as usual, a disturbance in one of the electrolytes requires repeating the test to rule out a lab error, and ordering additional tests to understand the source of the problem - and it's always important to think about regular medications you take, because specifically for chemistry, medications are one of the common causes of abnormal results.

## Kidney function

Our kidneys' job is to filter the blood in order to remove waste through the urine, to maintain the body's balance of fluids and salts, and to help regulate blood pressure.

So as we said, electrolytes by themselves provide information on kidney function;

in kidney function we have 3 measures in the chemistry panel:

Creatinine - it's like a waste product created by our muscles that's supposed to be cleared through the kidneys. A low value doesn't mean much, other than being a sign of low muscle mass, but if it's high that indicates a problem in kidney function.

And another measure that isn't something measured directly from the blood but is calculated in the lab based on the rest of the test results - the GFR, or glomerular filtration rate, which gives a direct measure of kidney function. If it's low - that's a sign of impaired kidney function, meaning the kidney isn't filtering the blood at the desired rate.

And another measure you'll see on tests is urea or BUN - both numbers reflect exactly the same thing, just in different units - they're protein breakdown products, and they too rise in kidney failure, but they can also rise with dehydration or very high protein intake.

Sometimes a chemistry panel also includes part of liver function, but some HMOs don't - in any case we'll talk about all of liver function in the next video, and there will also be a video explaining the blood lipid test, so subscribe to the channel so you don't miss them!

I hope this video helped you. I invite you to read part 1 - how to read your complete blood count. Feel free to write me questions below and I'll answer. A reminder to subscribe to the channel. And see you in the next video!