Understanding Your Lab Work

A guide to your lab work

If you’ve been diagnosed with chronic kidney disease (CKD), thorough testing can help you and your healthcare team understand what is going on inside your body and whether or not your treatment plan is working as well as it should.

Your doctor will perform different tests based on whether you are in the early or later stages of kidney disease. People in the earlier stages of kidney disease undergo tests that measure their kidney function. People in the later stages of kidney disease and people on dialysis are tested to see if their treatments are effective. If you are a DaVita® patient, you can see your lab results on the DaVita Health Portal™ and share them with your kidney care team. Below are some of the most common tests your doctor may order for you, when they are performed and what the results mean.

Serum Creatinine

  • Purpose: To determine how much creatinine is in the bloodstream.
  • Normal range: .8 to 1.4 milligrams per deciliter (mg/dl).
  • How this test is conducted: A blood sample is taken and sent for analysis.
  • When this test is performed: Throughout the early stages of chronic kidney disease and the later stages, including end stage renal disease (ESRD).

Creatinine is a waste product that is passed through the kidneys. It is a by-product formed by muscle contractions. It also comes from protein foods we eat, mostly from muscle meats. Women produce less creatinine than men because women have less muscle tissue. When your kidneys are not getting rid of creatinine, it remains in the bloodstream. Increased levels of creatinine may signal that your kidneys aren’t eliminating this waste, leaving it in the body.

GFR — Glomerular Filtration Rate

  • Purpose: To determine how much kidney function a person has.
  • Normal range: 90+, with little or no protein or albumin in urine.
  • How the test is conducted: This test is a calculation based on your creatinine level, age, race, gender and other factors.
  • When this test is performed: Throughout the early stages of CKD and the later stages, including ESRD.

The glomerular filtration rate (GFR) is a test that measures your kidney function. The result tells your doctor what stage of chronic kidney disease you are experiencing. Your doctor will calculate your GFR by using your creatinine level, age, race, gender and other factors. The GFR is an important test because in order to treat your condition effectively, your doctor must know what stage of kidney disease you are experiencing.

People in stage 1 kidney disease can have a GFR of 90+. However, there may be protein or albumin in their urine. Although people with high GFRs have plenty of kidney function, damage still occurs over time. As the kidneys become more damaged, the GFR will decrease. Changes to your GFR will tell your doctor how fast or slow your condition is progressing.

Stage

GFR Level

Description

Stage 1

90 mL/min or more

Healthy kidneys or kidney damage with normal or high GFR

Stage 2

60 to 89 mL/min

Kidney damage and mild decrease in GFR

Stage 3

30 to 59 mL/min

Moderate decrease in GFR

Stage 4

15 to 29 mL/min

Severe decrease in GFR

Stage 5

Less than 15 mL/min or on dialysis

Kidney failure

Microalbumin

  • Purpose: To detect a protein called albumin in the urine, which may indicate kidney damage.
  • Normal range: Almost no albumin should be detected.
  • How this test is conducted: A urine sample is taken from the person being tested.      
  • When this test is performed: In the early diagnostic stage of chronic kidney disease. Yearly for people with diabetes or high blood pressure.

The microalbumin test detects very small amounts of albumin in the urine. Albumin is protein. One of the early signs of damaged kidneys is the presence of albumin in the urine.

Damage to the tiny blood vessels in the kidneys allow albumin to leak into the urine. Diabetes and high blood pressure are two conditions that can damage these vessels. If not managed properly, the damage can accelerate over time. Increased microalbumin levels can mean you are in an early stage of kidney disease.

BUN — Blood Urea Nitrogen

  • Purpose: To detect elevated waste levels in the bloodstream, which is an early sign of reduced kidney function.
  • Normal range: 7 to 20 milligrams per deciliter (mg/dl)
  • How this test is conducted: A blood sample is taken and sent for analysis.
  • When this test is performed: In the diagnostic stage, the early stages of chronic kidney disease and the later stages, including end stage renal disease (ESRD), to measure effectiveness of treatment.

The blood urea nitrogen (BUN) test is an important diagnostic tool. Chronic kidney disease happens over time, but many people do not know they have it. This is because symptoms in the early stages of the disease may go unnoticed. An early diagnosis is important so that treatment can begin. Waste in the blood can be the first signal that your kidneys aren’t working as well as they should. The BUN test measures the amount of urea in your bloodstream. Urea is a waste product left over from the protein you eat, which is normally eliminated through the kidneys. High levels of urea mean your kidneys are not getting rid of waste and it remains in the body. This could make you feel tired and ill.

CCr — Creatinine Clearance

  • Purpose: To determine how well the kidneys are filtering creatinine.
  • Normal range: For men, normal values can range from 97 to 137 milliliters per minute. For women, normal values can range from 88 to 128 milliliters per minute.
  • How this test is conducted: A blood sample is taken and the person tested in addition to a urine sample. Both samples are sent for analysis.
  • When this test is performed: When a person is starting dialysis or to assist with a nutritional assessment.

The creatinine clearance test (CCr) measures the amount of creatinine in your urine and blood. A urine sample and blood sample are needed for this test. Your urine sample will tell your doctor how much creatinine your kidneys are eliminating. A blood sample will be taken before or after you take your urine sample and analyzed for the amount of serum creatinine. Both measurements will be used to calculate how well your kidneys get rid of waste.

Hb — Hemoglobin

  • Purpose: To determine the amount of hemoglobin in red blood cells and screen for anemia.
  • Normal range: In an adult, 12 to 18 grams per deciliter of blood.
  • How the test is conducted: A blood sample is taken and sent for analysis. This test is often part of a comprehensive test called a complete blood count (CBC) or complete blood test.
  • When the test is performed: Throughout the early stages of chronic kidney disease and the later stages, including ESRD.

The hemoglobin test is part of a complete blood count (CBC), which is a comprehensive exam that looks at the different cells found in the blood. Each type of cell—white blood cells, red blood cells and platelets—undergo a panel of tests. These tests will determine the number, size and physical characteristics of the cells. If you have renal disease, your kidney doctor will look at your hemoglobin and hematocrit levels, both taken from analyzing your red blood cells.

Hemoglobin is a protein found in your red blood cells. It helps transport oxygen throughout the body. Low levels can signal anemia. Patients in the later stages of renal disease are at risk for anemia because damaged kidneys lose the ability to make a hormone called erythropoietin. This hormone is required for red blood cell production. In addition, their diets are often restricted in the amount of protein they can have. Protein is an important source of iron, which is also required to make red blood cells. If your hemoglobin levels are low, your doctor will prescribe iron supplements and/or Epogen® (EPO), the man-made form of erythropoietin.

Hct — Hematocrit

  • Purpose: To determine the percentage of red blood cells in the blood and screen for anemia.
  • Normal range: For adult females the range is usually 36% to 47%, for adult males the range is 40% to 53%. For dialysis patients the recommended target hematocrit range is 33% to 36%.  
  • How this test is conducted: A blood sample is taken and sent for analysis. This test is often part of a comprehensive test called a complete blood count (CBC) or complete blood test.
  • When this test is performed: Throughout the early stages of chronic kidney disease and the later stages, including ESRD.

Hematocrit measures the percentage of blood that is made up of red blood cells. A low hematocrit level may indicate your body is not making enough red blood cells. Red blood cells carry oxygen throughout the body. This oxygen provides energy to the cells of the body. If your body has low amounts of red blood cells, your body’s cells aren’t getting enough oxygen to do their jobs. This can lead to feeling tired and having no energy.

URR — Urea Reduction Ratio

  • Purpose: To measure how much urea was removed during a hemodialysis session.
  • Target range: URR should be more than 65%.
  • How this test is performed: A blood sample is taken at the start of a dialysis session and another sample is taken afterwards.
  • When this test is performed: Once every 12 to 14 dialysis sessions, this is approximately once a month.

Your urea reduction ratio (URR) is a test that will tell your health care team how well dialysis is cleaning your blood. Dialysis removes waste products like urea and excess fluid. If too much waste or fluid remains in your blood, you will feel ill. By comparing the urea levels in your blood samples before and after a single hemodialysis treatment, a member of your health care team can calculate your URR. If it falls below 65% or the goal your physician has set, your health care team may adjust the rate of flow on the dialysis machine or recommend increasing the amount of time you spend dialyzing.

Kt/V

  • Purpose: To determine effectiveness of dialysis treatment.
  • Target range for hemodialysis patients: More than 1.2.
  • Target range for peritoneal dialysis patients: More than 2.0.
  • How this test is conducted: For hemodialysis, a blood sample is taken at the start and end of a dialysis session. Information about your treatment is collected, and a computer calculates the Kt/V result. For peritoneal dialysis (PD), a blood sample is taken along with a sample of the PD fluid and the volume removed over 24 hours.
  • When this test is performed: Once a month for hemodialysis patients and once every four months for PD patients or after a prescription change.

Kt/V is a mathematical formula, where:

“K” = clearance (the amount of urea your dialyzer has removed (liters/minute)) multiplied by

“t” = time (the duration of treatment (minutes)) divided by

“V” = volume (the amount of body fluid (liters)).

Kt/V is another test that tells you how well dialysis is cleaning your blood. Kt/V is considered more accurate than URR because it takes into account your size, treatment time, blood flow rate, how much urea your body makes during dialysis and the extra urea and fluid removed in your dialysis session.

Hitting the target range for your Kt/V is important. Good, effective dialysis can help you feel better and stay healthier. If you’re not hitting the target range, your health care team will recommend adjustments to your dialysis treatment.

A1c — Glycosylated Hemoglobin Test, also known as Hemoglobin A1c

  • Purpose: To determine average blood glucose levels over a two to three month period. This test is for people with diabetes.
  • Target range: American Diabetes Association goal is less than 7.0 gm/dl for good blood glucose management for diabetics.
  • How this test is conducted: A blood sample is taken and sent for analysis.
  • When this test is performed: This test is done when you are first diagnosed with diabetes and then 2 to 4 times a year thereafter.

The A1c is a test performed on people with diabetes. The A1c gives your doctor a snapshot of your average blood glucose levels for the past two or three months.

Diabetes is the leading cause of chronic kidney disease. High glucose in the bloodstream can damage the tiny blood vessels in the kidneys. Keeping your blood glucose down is important in preventing further damage to your kidneys. The A1c can tell you and your doctor how well you are managing your diabetes and whether the treatment plan you are following is working.

Blood electrolyte levels

  • Purpose: To measure the levels of electrolytes (sodium, potassium, calcium, phosphorus) in the body that help move nutrients and waste in and out of cells.
  • Normal range: Sodium: 135 to 145 mEq/L. Potassium: 3.5 to 5.0 mEq/L. Calcium: 8.5 to 10.5 mg/dL. Phosphorus: 3.0 to 4.5 mg/dL. The goals for people on dialysis vary from some of these levels—potassium goal 3.5 to 5.5, calcium 8.4 to 9.5, phosphorus 3.5 to 5.5.
  • How the test is conducted: A blood sample is taken and sent for analysis.
  • When this test is performed: During stages 3, 4 and 5 of kidney disease, when the renal diet is prescribed or if the person is on dialysis.

Sodium, potassium, calcium and phosphorus are minerals that are important for the body to function correctly. If the levels of these minerals become out of balance, they can cause health complications. A blood electrolyte test can tell your doctor and your dietitian if these levels are too high or too low. The kidneys help keep these minerals in balance by getting rid of any excess. But if you have chronic kidney disease, or are on dialysis, your kidneys may have a difficult time managing the electrolyte levels properly. This can lead to complications such as excess fluid retention, erratic heartbeats and bone disease.

People in the later stages of kidney disease, or who are on dialysis, are often placed on a special diet. This renal diet will help keep your electrolyte levels in balance by restricting food that is high in sodium, potassium, calcium and phosphorus. The blood electrolyte test can also help you and your dietitian make any necessary adjustments to your diet.

Summary

Knowing your lab results can help you understand what is going on in your body. Your dietitian, doctor and the rest of your healthcare team will monitor your test results and recommend dietary adjustments or make changes to your treatment. If you don’t know what your numbers are, or have questions about these tests, be sure to ask a member of your kidney care team for more information. Also get your lab results on the DaVita Health Portal™ when you are a DaVita patient.

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