Important Laboratory Test and Expected Values for People on Dialysis
When the kidneys fail, many functions in the body are affected. With the use of dialysis, dietary modifications and medications, your medical team tailors a treatment plan to best meet your body's needs. Your physician will order laboratory test on your blood in order monitor your health and the effectiveness of your treatment plan.
Below is a list of the most common conditions associated with kidney failure, the lab test performed to monitor those conditions, what the lab test mean, and what you can do to make the most of your treatment plan.
Dialysis Adequacy measures the effectiveness of your dialysis treatments. It is important to receive enough dialysis to feel well and minimize the side effects of kidney failure. We "measure" dialysis adequacy in a number of ways:
- How well you feel
- How much excess fluid you may have
- How well your blood pressure is controlled
- Results of certain lab values (discussed below)
BUN (Blood Urea Nitrogen)
The BUN is a measurement of waste products in the blood. Normal values for a person with kidney failure vary according toprotein intake. Your values may range from 20-80 mg/dl when the labs are drawn prior to your dialysis treatment. This lab measurement is used in the adequacy calculations listed below.
URR (Urea Reduction Ratio)
URR is calculated from BUN levels, one drawn before and one drawn after your dialysis treatment. The URR is generally measured once per month. If you are dialyzing well, your URR should be at least 65%.
Another way to measure the effectiveness of your dialysis treatments is Kt/v. It is calculated using a number of values including your weight, URR, the dialyzer clearance, and dialysis time. If you are dialyzing well your Kt/v should be at least 1.2.
Your URR and Kt/v will be checked monthly or more often if indicated by low levels, unstable levels, or changes in your condition.
Dialysis adequacy may be affected by:
- The length of your physician ordered dialysis treatment.
- It is important to dialyze for the prescribed time.
- The frequency of your dialysis treatments.
- It is important not to miss any treatments.
- How well your access works.
- We continually monitor the function of your vascular access. If problems or changes are noted, you may be scheduled to see an access specialist. It is important to keep those appointments.
- How much fluid you gain between treatments.
- Gaining a large amount of fluid between treatments will make your dialysis treatment less effective and ultimately weaken your heart. It is important to follow your fluid guidelines.
This is the oxygen carrying component of the red blood cell (RBC). The hemoglobin is frequently low in people with kidney failure because the kidneys no longer make the hormone erythropoietin. This hormone stimulates the bones to make red blood cells. We are able to replace this hormone with medications that are given during dialysis. In addition to the low hormone level, the elevated levels of toxins in the blood cause the RBC to have a shortened life span in the person with kidney failure.
Your hemoglobin will be monitored monthly and more often if indicated by low or unstable levels. The ideal level for your hemoglobin should be around 10g/dl. Recent research has demonstrated that levels above 13g/dl may be harmful to patients on dialysis.
This hemoglobin may be affected by:
- How much erythropoietin your body continues to make on its own and the amount of the medication you are given to replace the hormone.
- The amount of iron in your blood.
- Blood loss
- Inadequate dialysis
Iron Saturation and Ferritin
The body requires iron to make red blood cells. Frequently people undergoing dialysis have low iron levels as a result of chronic blood loss associated with hemodialysis.
Your iron levels will be monitored every 3 months or more often if indicated by low or unstable levels. The ideal range for the iron saturation is greater than 20 %. The ideal range for ferritin is 100-500 ng/ml.
There is little you can do to specifically change your iron and hemoglobin levels. The medications which control these levels are given by the dialysis staff, during your dialysis treatment. It is important, however, to maintain good overall health. Staying healthy helps your body to function more normally. Things you can do to stay healthy include:
- Avoid infections
- Get plenty of rest
- Exercise regularly
- Follow your doctor's orders regarding your dialysis treatments and medications
Albumin is a complex protein made from the foods you eat each day. People on dialysis may have a low albumin level due to poor appetite or low protein food choices. Albumin levels may also be low due to infections or other diseases. A low level of albumin may lead to health problems such as difficulty fighting off infections.
Your albumin level will be monitored monthly. The ideal level is greater than 4 g/dL. If your level is less than 4, your dietitian will talk with you to identify ways to increase the amount of protein in your diet.
Potassium is a mineral in your blood that helps your heart and muscles work properly. When your kidneys do not work properly, potassium may build up in your blood. A potassium level that is too high or too low may weaken muscles and change your heartbeat. If the levels are high enough, it may cause your heart to stop altogether. To avoid these problems it is necessary to restrict the amount of potassium in your diet.
Your potassium level is measured monthly or more often if indicated by high or unstable levels. The ideal range for potassium in a person on dialysis is 3.5-5.5. If your potassium is elevated, your dietitian will talk with you to identify ways to decrease your potassium level.
Bone and Mineral Metabolism
A little known function of the kidneys is managing the minerals in your body. When the kidneys fail, a complex chain of events begins that may ultimately result in severe bone disease and calcification (hardening) of your veins and arteries.
When the kidneys work normally, they work together with the bones, parathyroid gland and intestines to maintain a balance between the minerals calcium and phosphorus. The parathyroid gland monitors blood calcium and phosphorus. When the phosphorus is too high or the calcium is too low, the parathyroid gland sends a hormone message (parathyroid hormone or PTH) to the body. This message tells the kidneys to convert more vitamin D to its active form and to increase the amount of phosphorus that is excreted in the urine. The hormone tells the bones to release some calcium into the blood. The increased levels of active vitamin D cause more calcium to be absorbed from the food in the intestine. As the calcium is absorbed from the intestine, it drags along additional phosphorus with it. When the kidneys work properly, the excess phosphorus is excreted in the urine. All of these activities continue until the mineral levels are stabilized.
When the kidneys are taken out of the process, they no longer activate vitamin D , therefor additional calcium is not absorbed from the intestines. Phosphorus is no longer excreted by the impaired kidneys causing those levels to rise quickly. The elevated phosphorus and low calcium levels continue to stimulate the body to release PTH. This leads to an overworked and enlarged parathyroid gland. Since there is no additional calcium absorbed from the intestines, the bones continue to release calcium into the blood stream to maintain blood calcium levels. As the calcium is removed from the bones, they become weak and brittle. As the phosphorus continues to rise, the body begins to store the excess phosphorus in the walls of the veins and arteries resulting in hardening of those vessels. As tissues receive less blood supply from the hardened blood vessels, poor wound healing and tissue death may occur. The tissue death may result in severe tissue ulcerations, amputation and even death in some cases.
As you can see, this is a very complicated process. Avoiding these adverse events requires careful management by your dialysis team and careful adherence on your part to your treatment plan.
The treatment plan typically includes a combination of several of the following:
- Consistently taking medications that stop the phosphorus from being absorbed from the food in your intestines.
- Limiting the amount of phosphorus in your diet.
- Taking an active vitamin D supplement. These are not the vitamins you buy over the counter, but are prescribed to you by your kidney doctor.
Once the disease has progressed other measures may include:
- Taking medications that suppress the parathyroid gland from producing its hormone.
- Surgical reduction of the parathyroid gland.
Depending on how your body reacts, you may need some or all of the interventions listed above to control this cycle. The importance of following the treatment plan as prescribed cannot be overstated. This condition often has few if any symptoms until the disease is far progressed and the results of the disease are irreversible.
The lab values associated with bone and mineral metabolism are phosphorus, calcium, and parathyroid hormone (PTH). Calcium and Phosphorus levels are drawn monthly or more often if the levels are unstable. The PTH level is drawn quarterly or more often if the levels are unstable. The ideal range for Calcium is 8-10mg/dl, the ideal range for phosphorus is 3-5mg/dl, and the ideal range for PTH is 150-600pg/ml. Some physicians feel a tighter control of PTH is necessary and may recommend a maximum level of 300pg/ml.