Ah, yes... the monthly laboratory value "report card." What do you do with it? Do you use the numbers to pick your lottery ticket? Is it good for scrap paper? Do you understand what any of the numbers mean? Do you pretend to be asleep in your dialysis chair when they are handed out because you just don't want to deal with the explanation?
Some patients feel they have no control over their lab values, and they are "yelled at" monthly for not meeting certain levels. What do these values mean to you?
Drawing Your Lab Values
Let's start by figuring out why they even do monthly lab tests. No, they don't sell your blood to others for money! Drawing of blood for monthly laboratory values is mandated by the federal law that pays for your dialysis care. It is also required at certain times during your post-transplant follow-up.
How they draw the blood for your lab values is important. If you are on dialysis, your pre-treatment blood sample should be drawn before the machine has started the dialysis process and before anything (heparin or saline, for example) has been added to your vascular access line. The post-treatment sample should be drawn after your dialysis time is completed but before the needles are removed.
If your are not on dialysis when the sample is taken, your blood should be drawn while you are in a sitting position; a tourniquet (an elastic band placed above the site of the needle insertion) is used initially to identify the best spot from which to draw the blood. Be sure to tell the person drawing your blood about your fistula or graft location (even if you are not presently using it) so that the tourniquet does not damage your access site.
Colored Tube Caps and "Spun Down"
The number of tubes (containers) needed when your blood is drawn is determined by the tests that are ordered. You may notice that the tubes have different color caps. The color of the cap indicates what kind of preservative the tube contains, or whether no preservative is present. Each different type of blood test requires a specific color tube. This ensures that your blood sample is accurate when it is analyzed.
Most blood samples have to be "spun down" (put in a centrifuge machine, in little holders, and rapidly turned around to separate the red blood cells from the water-like part) before they can be analyzed. The tubes ensure that the blood can be held correctly during transport to the lab or while waiting to be spun down until it can be analyzed.
Kinds of Lab Values
Lab values are used primarily to ensure that you are receiving adequate care. There are four kinds of laboratory values (see Table 1):
single snapshot
double draw
moving target
sorting
Table 1. Types of Laboratory Values
Type | Some Examples | Why Used |
Single Snapshot | Potassium, glucose, phosphorus, calcium. | To take a one-time, single look at a value; value may change slowly or rapidly. |
Double Draw | Blood urea nitrogen (BUN). | To show changes pre- and post-treatment. |
Moving Target | PTH, iron saturation %. | To monitor changes over time to keep within recommended levels.. |
Sorting | Tissue typing (HLA), hepatitis B or C. | To determine which group you belong to. |
Single Snapshot and Double Draw
A single snapshot is used to measure a single moment in time. For example, your serum potassium or serum glucose (blood sugar) measures only what your value is at the time of the blood draw and can be very different in an hour!
An example of a double draw would be blood urea nitrogen (BUN), which shows how much accumulated waste products are present because your kidneys are not working properly (or not working at all!). Before and after dialysis treatment, we would measure BUN. The difference between the two values must show at least a 65% reduction (decrease) in waste products. If it does not, we need to understand why so we can fix the problem. Perhaps your vascular access is damaged or clotted. Perhaps you did not stay for your entire prescribed treatment or missed a treatment. Maybe the solutions we use in your dialysis machine (or peritoneal dialysate if you are on peritoneal dialysis) need to be changed.
Moving Target and Sorting
A moving target lab value is used to check your progress over time. An example of this would be parathyroid hormone (PTH). We would look at your monthly PTH values over time to check the status of your bones and prevent them from becoming weak due to high PTH levels.
A sorting laboratory value would be used to "classify" or "sort" you. An example would be using a blood draw to determine your tissue typing or antibody class to help match you with a kidney that would have the lowest rejection risk.
What Affects Your Lab Values?
Many things can change your lab values each month:
Diet is a big factor because what you eat must be processed by your body. What you eat has to be matched to what your kidneys can do. The diet also has to provide what you need to stay healthy and keep your body in top shape. For example, a low serum albumin might mean you are not eating enough protein to repair and maintain your muscle tissue.
Fluid accumulates in your body when you can't make urine or your urine doesn't contain the waste products. Too much fluid can put extra stress on your heart between treatments by forcing it to pump harder or more times each minute.
Many laboratory values are also affected by the medication you take. For example, phosphate binders remove the phosphorus from your food by binding it in your intestines and removing it through your stools. When you take your binders correctly, less phosphorus shows up in the blood, and your laboratory value is lower.
Other laboratory values can be affected by infection or inflammation. We can sometimes tell that you have a problem before you even feel it! Sudden rises in serum potassium or C-reactive protein can indicate that substances are being released from cells inside your body that are being destroyed or injured because of problems like sepsis (a blood infection) or kidney rejection (cells in the kidney are dying).
Conclusion
Laboratory values are only one of many ways that your healthcare is monitored. These values, like many aspects of kidney care, have clinical guidelines and standards for care that have been analyzed and recommended by experts. Visit the National Kidney Foundation website (www.kidney.org) for information on the wide variety of quality care standards that are currently published or in progress. Go to the American Kidney Fund (www.kidneyfund.org) and other websites for patient education materials, or ask your healthcare team.
So, the next time you are given a laboratory report, make it work for you! Consider asking a member of your healthcare team what the values mean for you. Each person's laboratory values are a unique picture of you, your treatment, and your ability to control some aspects of your health. Lab values can tell you a great deal about your treatment plan, predict the risk of health complications (like bone and heart disease), and even hold the possibility of making you feel better as you work to bring them closer to normal levels. Get your money's worth and ask what your lab values mean for you!
About the Author
Judy Beto, PhD, RD, is Research Associate, Division of Nephrology and Hypertension, Loyola University Medical Center, Maywood IL.
Last Updated March 2007