Interpreting Common Labs

Lab work is something people with heart failure are used to being drawn. Every three, six, or twelve months we have lab work drawn to check the effectiveness of medication and certain levels to make sure we are stable. There are a few lab values that are important to know about and understand, not only for our own knowledge but also to help us understand the decisions our doctors make when the lab values are abnormal. While this is not all-inclusive, here are a few labs you should be familiar with.

Brain natriuretic peptide

Brain natriuretic peptide (BNP) is one of the most common lab values your doctor will use to see the effectiveness of your treatment of heart failure. Fun little fact, while BNP is a cardiac enzyme, it was first discovered in the brain before scientists found it originated from the heart, which is why it is called brain natriuretic peptide. Normal levels can vary slightly depending on your institution’s guidelines, but according to the Cleveland Clinic, normal levels for a person aged 0-74 are less than 125 pg/mL and for ages 75-99 normal is less than 450 pg/mL.¹

If you have heart failure, levels for people under 50 years old above 450 pg/mL and over 50 years old above 900 pg/mL could mean your heart function is unstable. This does not mean if you have a normal level you should be asymptomatic of heart failure. You could still have edema or other symptoms and have a normal BNP. If it is abnormal, or normal but you have symptoms of heart failure despite treatment, talk to your physician about treatment options.

Potassium

Potassium, especially for those on certain diuretics, is another important lab test to have drawn and understand. Generally, potassium is regulated by the kidneys and the body keeps it at normal levels by itself. When taking diuretics, you can throw off your potassium levels quickly without your body having time to regulate it.

Normal blood levels of potassium are 3.6-5.2 mmol/L. Low or high potassium can cause severe dysrhythmias which could be lethal so it is important to make sure these levels stay within the normal limits. If you take diuretics or have issues with potassium levels, make sure to keep all lab appointments and talk to your physician about how to keep your potassium level within normal limits.

Creatinine

The last lab we will look at is creatinine which measures kidney function. Why is kidney function important to monitor for someone with heart failure? There are a lot of risk factors for kidney failure related to heart failure. With reduced pumping ability of the heart, pressure and fluid can build up in the kidneys giving you increased risk of kidney failure. Diuretics put a lot of extra work on the kidneys which can cause kidney failure over time. Medication we take other than diuretics are considered nephrotoxic, or toxic to the kidneys.

Yes, there are a lot of medications that can cause kidney damage or failure, but that doesn’t mean they will. Do not stress about it, just be aware and work with your physician to minimize the risk of kidney damage. The normal level of creatinine is 0.6-1.2 mg/dL in men and 0.5/1.1 mg/dL in women. The reason for the difference in men and women is because creatinine is relative to muscle mass and in general men have more muscle mass than women. As always, with numbers outside the normal range, talk to your physician about it before stressing or trying to fix it yourself.

Three of the most important labs

There are a lot of tests everyone with heart failure will have drawn and should know about, but these are three of what I would consider the most important. It is good to understand lab values so you know when and why you could be out of the normal range, but it is never good to try to correct them without your doctor being involved in the method of how you do it. Hopefully, this helps you understand these lab values better and motivates you to research other lab values on your own.