Blood Urea Nitrogen (BUN)

Blood Urea Nitrogen (BUN)

• Urea is a nitrogen-containing compound, a waste product from protein metabolism in the liver.
• The Liver produces urea when it breaks down proteins and amino acids.
• The kidneys excrete urea from the body through urine.
• The BUN test is commonly used to assess kidney function.

Causes of Increased Urea Levels

• Kidney dysfunction or failure impairs the ability to filter and excrete urea, leading to accumulation in the blood.
• Excessive protein intake can increase urea production as the liver metabolizes more protein
• Reduced blood flow to the kidneys due to dehydration can decrease urea excretion, causing levels to rise.
• Gastrointestinal bleeding can increase urea levels.
• Conditions like sepsis or trauma can increase protein breakdown, leading to higher urea production.
• Certain medications can increase urea levels.
• Reduced blood flow to the kidneys due to heart failure can impair urea excretion.

Causes of Decreased Urea Levels

• A low protein diet reduces the amount of urea produced by the liver.
• Impaired liver function (e.g., cirrhosis, hepatitis) reduces the liver's ability to produce urea.
• Excessive fluid intake can dilute urea levels in the blood.
• Inadequate protein intake or malabsorption can lead to lower urea production.
• Increased blood volume and enhanced kidney function during pregnancy can lower urea levels.

Biological Role

• Urea is the primary nitrogen-containing waste product in mammals, including humans.
• Urea is produced in the liver during the urea cycle.
• During this process, toxic ammonia (from protein metabolism) is converted into urea, which is less toxic and more soluble in water.
• Urea is transported to the kidneys, where it is excreted in urine.
• This process helps maintain nitrogen balance in the body.

Normal Value

• The normal value of urea is between 10_50mg/dL.
• This value becomes higher with age.

Creatinine

• Creatinine is a waste product generated from the normal breakdown of muscle tissue.
• Creatinine is produced at a relatively constant rate.
• Creatinine is primarily filtered out of the blood by the kidneys and excreted in urine.
• Creatinine levels in the blood and urine are important indicators of kidney function.

Formation of Creatinine

• Creatinine is derived from creatine.
• Creatine is a molecule stored in muscles that provides energy for muscle contraction.
• When creatine is broken down, it forms creatinine as a byproduct.
• The production of creatinine is proportional to muscle mass.
• Individuals with more muscle mass tend to have higher creatinine levels.

Role of Creatinine

• Creatinine itself has no significant function; it is simply a waste product.
• Creatinine's primary importance lies in its use as a marker for kidney function.

Measurement of Creatinine

• Creatinine levels are measured through blood and urine tests.
• Blood Creatinine Test measures the amount of creatinine in the blood.
• Urine Creatinine Test measures the amount of creatinine excreted in urine over 24 hours.
• Creatinine Clearance Test compares blood and urine creatinine levels to estimate how well the kidneys are filtering waste.

Normal Creatinine Levels

• For men, normal blood creatinine levels are 0.6–1.2 mg/dL.
• For women, normal blood creatinine levels are 0.5–1.1 mg/dL.

Clinical Significance

• Elevated blood creatinine levels often indicate impaired kidney function, as the kidneys are not filtering waste effectively.
• Conditions like acute kidney injury (AKI) or chronic kidney disease (CKD) can cause elevated creatinine levels.
• High creatinine levels can also result from excessive muscle breakdown, such as in rhabdomyolysis (a condition caused by muscle injury).
• Low creatinine levels may indicate reduced muscle mass, malnutrition, or certain liver conditions.
• Creatinine levels are used to estimate the glomerular filtration rate (eGFR), which measures how well the kidneys are filtering blood.
• A lower eGFR indicates reduced kidney function.

Factors Affecting Creatinine Levels

• Creatinine levels tend to decrease with age due to reduced muscle mass.
• Men typically have higher creatinine levels than women because they generally have more muscle mass.
• A high-protein diet can temporarily increase creatinine levels.
• Some drugs, like NSAIDs or chemotherapy agents, can affect creatinine levels.

Calculations

• ΔΑ Sample - ΔΑ Blank x 2 (Standard conc.) = mg/dL of (Creatinine in sample) / ΔΑ Standard- ΔΑ Blank
• Conversion factor: mg/dL x 88.4 = µmol/L