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

September 29, 2021 Updated: December 29, 2021 6 min read

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.

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