Med-Surg - Cardiovascular System, part 4: Diagnostic Tests - Labs

by Cathy Parkes September 29, 2021 Updated: March 01, 2022 11 min read 3 Comments

This article covers cardiovascular lab value ranges for med-surg. The Med-Surg Nursing video series follows along with our Medical-Surgical Nursing Flashcards, which are intended to help RN and PN nursing students study for nursing school exams, including the ATI, HESI, and NCLEX.

Cool Chicken When you see this Cool Chicken, that indicates one of Cathy's silly mnemonics to help you remember. The Cool Chicken hints in these articles are just a taste of what's available across our Level Up RN Flashcards for nursing students!

A note about exact lab values

Ranges will vary across sources. It's important not to get hung up on these small differences because if you're given a lab value that is out of range on your nursing exam, it will be very out of range, either on the high or the low side. It is unlikely they will give you a borderline lab value.

Check with your textbook and with your professor to see what ranges you will be responsible for and what ranges you will be tested on.

Cardiac enzymes

Cardiac enzymes are enzymes released in the bloodstream in response to ischemia in the heart.

CK-MB

CK-MB is an enzyme found in the cardiac muscle, released upon damage to the cardiac muscle. Normally, CK-MB should be at 0% (not present). If CK-MB is elevated, it might be indicative of heart muscle damage. CK-MB would be elevated 3-6 hours after damage to the heart, and it will stay elevated for 2-3 days.

Myoglobin

Myoglobin is an oxygen-binding protein found in the heart muscle and skeletal muscle. Normally, myoglobin should be under 90 mcg/L. If myoglobin is over 90 mcg/L, that may be indicative of heart muscle damage. It can also be indicative of skeletal muscle damage, so it's not specific to the heart. Myoglobin will be elevated 2-3 hours after the damage and will stay elevated for approximately 24 hours.

Troponin T & I

Troponin, which includes both Troponin T and I, is a protein found in the heart muscle fibers. Troponin is the most specific enzyme for identifying ischemia of the heart and damage to the heart. It's considered the gold standard for helping to diagnose a myocardial infarction.

Troponin T should be under 0.1 ng/mL and Troponin I should be under 0.03 ng/mL.

These lab values are normally very low, almost 0. If they are elevated, of course, that means there is damage to the heart or ischemia of the heart. Troponin T and I will become elevated 2-3 hours after the damage occurs. Troponin T will stay elevated for about two weeks, while Troponin I will be elevated for 1 week.

Cool Chicken T for TWO (elevated levels within TWO hours, elevated for TWO weeks).

Cool Chicken “I” looks like the Roman Numeral ONE (levels elevated for 1 week).

Cholesterol

Cholesterol is a waxy, fat-like substance in the body. Excess cholesterol in blood can combine with other substances to form plaque and lead to atherosclerosis.

Total Cholesterol

The normal range for total cholesterol is below 200 mg/dL. Beyond total cholesterol, it's important to look at the patient's LDL and HDL levels.

Low-density lipoprotein (LDL)

LDL cholesterol is the "bad" cholesterol (L for lousy).

The normal range for LDL cholesterol is below 130 mg/dL. For high risk patients, the normal range for LDL cholesterol is below 100 mg/dL.

Triglycerides

Triglycerides are a type of fat. Extra calories are turned into triglycerides and stored in fat cells. Triglyceride ranges are usually taught with a male range and female range. The female range is 35 - 135 mg/dL and the male range is 40 - 160 mg/dL.

Elevated levels of triglycerides indicate an increased risk for atherosclerosis, heart disease, and myocardial infarction.

High-density lipoprotein (HDL)

HDL cholesterol is the "good" cholesterol (H for happy). The normal rate for female patients is greater than 55 and the normal rate for male patients is greater than 45.

Blood pressure

Blood pressure is a measure of the pressure of circulating blood on the walls of the blood vessels.

Normal

Most sources agree that the expected range for blood pressure is a systolic blood pressure under 120 and a diastolic blood pressure up to 80.

Elevated

Elevated blood pressure is a systolic blood pressure 120 - 129 AND a diastolic blood pressure up to 80.

Stage 1 hypertension

Stage 1 hypertension is a systolic blood pressure 130 - 139 OR a diastolic blood pressure 80 - 89.

Stage 2 hypertension

Stage 2 hypertension is a systolic blood pressure over 140 OR a diastolic blood pressure over 90.

Hypertensive crisis

A hypertensive crisis, or extremely high blood pressure, is a systolic pressure over 180 AND/OR a diastolic blood pressure over 120.

Blood panel and other cardiovascular lab values

The lab value ranges you need to know for red blood cells, platelets, Hgb, Hct, aPTT, PT, INR, D-Dimer, and hBNP will come up repeatedly during your cardiovascular med-surg studies. These ranges are explained below.

Red Blood Cells (RBCs)

Red blood cells are circulating cells that transport oxygen to the body's cells. The normal level for red blood cells is 4.2 - 5.4 million/uL for female patients and 4.7 - 6.1 million/uL for male patients.

Platelets

Platelets are blood cell fragments used to form clots in the body to stop bleeding. The normal level for platelets is 150,000 - 400,000 mm₃.

Hemoglobin (Hgb)

Hemoglobin is the iron-rich protein in red blood cells that carry oxygen. The normal level for hemoglobin is 12 - 16 g/dL for female patients and 14 - 18 g/dL for male patients.

Hematocrit (Hct)

Hematocrit is a measure for the percentage of the blood made up of red blood cells. The normal level for hematocrit is 37 - 47% for female patients and 42 - 52% for male patients.

Activated partial thromboplastin time (aPTT)

aPTT is a measure of clotting time including the intrinsic and the common pathways in the coagulation cascade. The normal range for aPTT is 30 - 40 seconds.

Prothrombin time (PT)

Prothrombin time is a measure of clotting time including the extrinsic and common pathways in the coagulation cascade. The normal range for prothrombin time (PT) is 11 - 13 seconds.

International Normalized Ratio (INR)

The international normalized ratio is a ratio of a patient's prothrombin time to a control PT level which is used to determine the effectiveness of warfarin therapy. The normal range for INR is 0.8 - 1.1.

D-Dimer

D-Dimer is the name for a protein fragment from the breakdown of a blood clot. The normal range for D-Dimer is less than 0.4 mcg/mL.

Human B-type Natriuretic Peptides (hBNP)

hBNP is a hormone produced in the ventricles, released in response to fluid overload. The normal range for hBNP is less than 100 pg/mL

Electrolytes

Electrolyte ranges are important to know in your medical-surgical studies. We cover the expected ranges for sodium, calcium, potassium, magnesium, chloride, and phosphorus below. To put it simply, electrolytes are salts that are important for the heart to work. Electrolytes are elements on the periodic table.

Sodium (Na)

Sodium is an electrolyte important for nerve and muscle function as well as maintaining fluid balance. The normal range for sodium is 136 - 145 mEq/L.

Calcium (Ca)

Calcium is an electrolyte important for bone and teeth formation, muscle and nerve function, as well as blood clotting. The normal range for calcium is 9 - 10.5 mg/dL.

Potassium (K)

Potassium is an electrolyte important for maintaining ICF (intracellular fluid volume) and regulating heart and muscle contractions. The normal range for potassium is 3.5 - 5 mEq/L.

Magnesium (Mg)

Magnesium is an electrolyte important for nerve and muscle function as well as biochemical reactions in the body. The normal range for magnesium is 1.3 - 2.1 mEq/L.

Chloride (Cl)

Chloride is an electrolyte important for maintaining fluid balance, and it is a component of digestive fluid (juices). The normal range for chloride is 98 - 106 mEq/L.

Phosphorus (P)

Phosphorus is an electrolyte important for bone and teeth formation, metabolism, and protein synthesis. The normal range for phosphorus is 3 - 4.5 mg/dL.


Full Transcript

Hi, I'm Cathy of Level Up RN. In this video, I'm going to begin my coverage of diagnostic tests related to the cardiovascular system. At the end of the video, I'm going to provide you guys a quiz to test your knowledge of some of the key concepts that I'll be covering in this video.

So in this video, I'm going to be talking about a lot of lab values associated with the cardiovascular system. And you can find all of these values and ranges in our Medical-Surgical Nursing Second Edition flashcard deck. You can also find this information in our Lab Values deck. And our Lab Values deck, in addition to giving you the expected range for each lab value, it also provides the significance of low or high values and provides some silly mnemonics or cool chicken hints to help you remember those values as well.

The first set of labs that I want to cover here are cardiac enzymes. So these are enzymes that are released into the bloodstream in response to ischemia of the heart, which occurs during a myocardial infarction. So the four labs that I would be familiar with include CK-MB, myoglobin, troponin T, and troponin I.

So CK-MB is an enzyme that is found in the cardiac muscle, and it is released upon damage to that cardiac muscle. Normally, we should see 0% CK-MB. So if this is elevated, that may be indicative of heart muscle damage. So this lab will be elevated three to six hours after damage to the heart, and it will stay elevated for approximately two to three days.

And then we have myoglobin, which is a protein that is found in the heart muscle as well as the skeletal muscle. So normally, myoglobin should be under 90. If it is over 90, that may be indicative of heart muscle damage. But it can also be indicative of skeletal muscle damage as well. So this is not specific to the heart. Myoglobin will be elevated about two to three hours after the damage and will stay elevated for approximately 24 hours.

Now, we have troponin T and I. So these are proteins that are found in the heart muscle fibers. And troponin is the most specific enzyme for identifying ischemia of the heart and damage to the heart. So troponin is really our gold standard for helping to diagnose a myocardial infarction.

Troponin T should be under 0.1.

Troponin I should be under 0.03.

So these are supposed to be very low, almost 0. If we have elevation, of course, that's going to mean that we have likely damage to the heart, ischemia of the heart. Troponin T and troponin I will become elevated two to three hours after the damage occurs. Troponin T will stay elevated for about two weeks.

So my little hint for how to remember this is, if you look at troponin T, T for two will help you remember it stays elevated for two weeks. And then troponin I, I looks like Roman numeral one, will help you to remember that troponin I stays elevated for one week.

All right. Now, let's talk about cholesterol.

So we want our patient's total cholesterol to be under 200. Then we need to look at their LDL and HDL levels.

So LDL stands for low-density lipoprotein. This is our bad or lousy cholesterol so L for LDL, L for lousy. And we want this value to be under 130. If your patient is at high risk for cardiovascular disease, then we really want it under 100.

And then, in terms of HDL, which is high-density lipoprotein, this is our good cholesterol so our happy cholesterol, so H for HDL and H for happy. We want this to be over 55 for females and over 45 for males.

And then we have our triglycerides, which should be between 35 and 135 for females and between 40 and 160 for males.

Now, let's talk about blood pressure.

So across all sources that I've seen, they all agree that the expected range for blood pressure is to have a systolic blood pressure under 120 and a diastolic blood pressure under 80. So that's pretty standard across the board.

However, when we start getting into blood pressure ranges for prehypertension, stage 1 and stage 2 hypertension, and a hypertensive crisis, those ranges will vary across sources. So we have our ranges here on the flashcard. However, you need to check with your textbook and with your professor to see what ranges you will be responsible for and what ranges you will be tested on as well.

Right. Let's go on and talk about other lab values associated with the cardiovascular system. So as I go through the expected ranges of these values, keep in mind that these ranges will vary slightly across sources. And it's important not to get hung up on these small differences because in all likelihood, if you're given a lab value that is out of range on your nursing exam, it will be very out of range, either on the high or the low side. They're not going to give you something kind of right there at the border. So again, don't get hung up on those small differences.

All right. Red blood cells, red blood cells should be somewhere between 4.2 and 5.4 for females. The male range is slightly higher, between 4.7 and 6.1.

Platelets should be between 150,000 and 400,000.

Hemoglobin should be between 12 and 16 for females and between 14 and 18 for males.

And then hematocrit should be between 37 and 47 percent for females and between 42 and 52 percent for males. And one thing that is helpful to me, when I was learning hemoglobin and hematocrit levels in nursing school, if you look at those ranges, the hematocrit numbers are approximately three times the hemoglobin numbers. So hopefully, that's helpful to you as well.

Next, we have aPTT, which is activated partial thromboplastin time. So this measures the clotting time of the intrinsic pathway and common pathway of the coagulation cascade. And the normal range of clotting time is somewhere between 30 and 40 seconds. If a patient is on heparin, then this will be extended. So with heparin, we would expect this aPTT number to be 1.5 to 2 times this amount. So it will vary between like 45 and 80 seconds.

Then we have PT, which is prothrombin time, and INR. And these are the numbers we're going to monitor if our patient is on warfarin. So prothrombin time measures the extrinsic pathway and the common pathway in that coagulation cascade. And the clotting time usually varies between 11 and 13 seconds. When a patient is on warfarin, then this will be 1.5 to 2 times this amount. So we would expect this clotting time to be somewhere between 17 and 26 seconds, roughly.

But the real number we're going to monitor, when the patient is on warfarin, is INR. So INR is normally about 1. But when a patient is on warfarin, we would expect this number to be between 2 and 3. So definitely, be paying attention to that number while the patient is on warfarin. And we're going to adjust their warfarin dose to get them into that 2 to 3 range for anticoagulation.

And then we have D-dimer. D-dimer is usually very low, under 0.4. D-dimer will be elevated in the presence of a clot, such as a DVT or a pulmonary embolism or PE.

And then the last number I want to go over here is hBNP. So hBNP is a hormone that is released by the ventricles in the heart in response to fluid overload. So if that heart is overloaded with too much fluid, it really stretches that heart, and that stretch causes the release of hBNP. So normally, hBNP should be under 100. If your patient's hBNP is over 100, that is indicative of heart failure because with heart failure, we end up with fluid volume overload in the heart that stretches the heart out and causes the release of more hBNP.

Within the diagnostic test section of our flashcard deck, you'll notice that we've included the normal ranges for electrolytes here. I'm not going to go over those here in this video. We will be covering electrolyte imbalances later on in this video playlist, and we'll talk about those lab ranges then. But it is here for your reference if you have our deck.

All right. You guys ready for a quiz? I've three questions for you. First question, which cardiac enzyme is most specific for diagnosing ischemia in the heart? If you said troponin, you're correct. Number two, what is the normal range for platelets? The answer is 150,000 to 400,000. Third question, what lab value is elevated in the presence of a clot? The answer is D-dimer. So again, normally, D-dimer is under 0.4. If it is elevated, that may be indicative of a clot in the body.

Okay. I hope this video has been super helpful, hope you liked the quiz questions, too. If so, be sure to like this video. Leave me a comment. And I'll see you when we talk about more diagnostic tests in my next video.


3 Responses

Simone
Simone

March 29, 2022

This information gave me a better understanding of cardiac enzymes. I know it will help me to pass my class test

Jocelyne
Jocelyne

March 01, 2022

Great job

Jocelyne
Jocelyne

March 01, 2022

Awesome I enjoyed the lecture.great tips for my upcoming exam

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