Glossary of Renal Terms*
Blood urea nitrogen (BUN)
The normal range is 8–20 milligrams (mg)/deciliter (dL) or 2.9–7.1 millimoles
(mmol)/liter (L). Urea nitrogen is a normal waste product in your blood. It comes from
the breakdown of protein from the foods you eat and from your body’s metabolism.
It is normally removed from your blood by your kidneys, but when kidney function slows
down, the BUN level rises. BUN also can rise if you eat more protein, and it can fall if
you eat less protein. BUN is actually the concentration of nitrogen (within urea) in the
serum and not in the blood. The concentration of nitrogen is dependent upon urea
production, which occurs in the liver, and tubular reabsorption, in addition to glomerular
filtration.
The BUN level is used to assess or monitor hydration status, renal function, protein
tolerance, and catabolism. Urine flow, which is affected by fluid balance and blood
pressure, can lead to changes in BUN. Dehydrated individuals who have a low urine
flow, which leads to low blood pressure, will likely develop an elevated BUN. In
addition, an individual with low blood pressure will develop low urine flow, which in
turn leads to a higher concentration of urea nitrogen in the blood.
The following are potential causes of elevated BUN:
 A high-protein diet
 Upper gastrointestinal bleed—blood is digested as dietary protein
 Administration of any drug with antianabolic effects
Calcium
The normal range is 8.5–10.7 mg/dL. Calcium is a mineral that is important for strong
bones. The normal adult body contains approximately 99.5% of its calcium in the bones
and the other 0.5% in the blood. These levels are tightly managed. However, in the
presence of kidney disease, the body is not as able to control calcium levels in the blood,
which leads to hypocalcemia or hypercalcemia.
Glomerular filtration rate (GFR)
The GFR is the volume of water filtered or “cleared” out of the plasma per minute
through the surrounding capillary walls into Bowman’s spaces. It is difficult to measure
accurately and typically is estimated using other markers.
Your GFR tells how much kidney function you have and is estimated from your blood
level of creatinine. If your GFR falls below 30, you will need to see a kidney disease
specialist, called a nephrologist. Your kidney doctor will speak to you about treatments
for kidney failure, such as dialysis or kidney transplant. A GFR below 15 indicates that
you need to start one of these treatments.
Hematocrit
The normal range is 33%–36%. Your hematocrit is a measure of the red blood cells your
body is making. A low hematocrit can mean that you have anemia and need treatment.
Hemoglobin
The normal range is 10.0–12.0 grams (g)/dL. Hemoglobin is the part of red blood cells
that carries oxygen from your lungs to all parts of your body. A low hemoglobin level
indicates you may have anemia and need treatment.
Microalbumin
The normal range is less than 30 mg. This is a sensitive test that can detect a small
amount of protein in the urine. It is measured by taking a single urine specimen or a 24hour urine collection.
Nephron
This is the functional unit of cells in the kidney. Each nephron is divided into:
 Glomerulus—filtering section of the nephron
 Proximal tubule—actively reabsorbs large quantities of water, glucose, amino acids,
uric acid, sodium, chloride, bicarbonate, and other electrolytes
 Loop of Henle—reabsorbs sodium and water
 Distal tubule—controls the amount of sodium, potassium, bicarbonate, and hydrogen
 Collecting duct—regulates the amount of water in the urine
The kidneys filter about 180 L of fluid each day. However, the kidneys only excrete
about 1.5 L of urine. About 99% of the glomerular filtrate is absorbed back into the
bloodstream.
The following solutes are not reabsorbed:
 Endogenous substances, such as creatinine and urea
 Exogenous substances, such as drugs
Parathyroid hormone (PTH)
The normal range is 10–60 picograms (pg)/milliliter (mL). PTH is the most important
hormone involved in calcium balance in the blood and body. When high levels of PTH
occur, the body is less active at resorption of calcium into the bones. This may result
from a poor balance of calcium and phosphorus in your body. It can cause bone disease.
Phosphorus
The normal range is 2.6–4.5 mg/dL. The bones hold 85% of the body’s phosphate, with
approximately 90% filtered by the kidney. In the presence of kidney disease, the body is
not able to control the levels of phosphorus in the blood. A high phosphorus level can
lead to weak bones.
Potassium
The normal range is 3.5–5.0 milliequivalents (Eq)/L. Potassium is a mineral in your
blood that helps your heart and muscles work properly. A potassium level that is too high
or too low may weaken muscles and change your heartbeat. Whether you need to change
the amount of high-potassium foods in your diet depends on your stage of kidney disease.
Protein-to-creatinine ratio
The normal range is <0.1. This estimates the amount of protein you excrete in your urine
in a day and eliminates the need to collect a 24-hour urine sample.
Serum albumin
The normal range is 3.5–5.0 g/dL. Albumin is a type of body protein. A low level of
albumin in your blood often is caused by infection or chronic disease. Eating adequate
protein is important to good health, but dietary protein alone will not increase serum
albumin levels.
Serum creatinine
The normal range is 0.7–1.5 mg/dL or 62–133 micromoles (μmol)/L. Creatinine is a
waste product in your blood that comes from muscle activity. It is normally removed
from your blood by your kidneys, but when kidney function slows down, the creatinine
level rises. Creatinine is a spontaneous decomposition product of creatine and creatine
phosphate. In a normal body, the rate of creatinine production equals its excretion. Serum
creatinine should vary little day to day in healthy person. Your doctor should use the
results of your serum creatinine test to calculate your GFR.
A rise in serum creatinine is almost always an indication of worsening renal function. It is
not influenced much by usual changes in diet or urine flow. Serum creatinine is a byproduct of muscle metabolism. Any metabolic condition that causes muscle loss, such as
cachexia, spinal cord injuries, or coma, may cause decreased creatinine production.
Transferrin saturation (TSAT) and serum ferritin
The normal range is TSAT 20% and ferritin >100. Your TSAT and serum ferritin are
measures of iron in your body. The amount of ferritin in the blood is directly related to
the amount of iron stored in the blood. Normal levels help build red blood cells.
Urine creatinine
The normal range can vary from 500–2000 mg/day, depending on age and amount of lean
body mass. This test estimates the concentration of your urine and helps to give an
accurate protein result. An abnormal or high value may indication declining kidney
function.
Urine protein
The normal range is 0–1+ or <150 mg/day. When your kidneys are damaged, protein
leaks into your urine. A simple test can detect protein in your urine. Persistent protein in
the urine is an early sign of chronic kidney disease.
 Normal ranges may vary depending on what laboratory performs testing or what
reference is consulted.
References and recommended readings
Drugs.com. Drug information online. Available at: www.drugs.com. Accessed December
10, 2012.
Mahan LK, Escott-Stump S, Raymond JL. Krause’s Food and the Nutrition Care
Process. 13th ed. St Louis, MO: Elsevier Saunders; 2012.
MedicineNet. We bring doctors’ knowledge to you. Available at: www.medicinenet.com.
Accessed December 10, 2012.
National Kidney Foundation™. Kidney disease. Available at: www.kidney.org. Accessed
December 10, 2012.
Traub SL, ed. Basic Skills in Interpreting Laboratory Data. 2nd ed. Bethesda, MD:
American Society of Health-System Pharmacists; 1996.
Review Date 12/12
R-0500