Biochemical Profile

Sample collection

• performed on serum

• blood collected in a red top tube, allowed to clot & centrifuged

Reference intervals

• established from healthy animals using appropriate statistical procedures

• most include 95% of healthy population (not all healthy animals will be in the normal range)

  • always interpret laboratory findings with what else you know about the animal

Types of laboratory error

• majority pre-analytical (ex: incorrect test ordered)

• some analytical (ex: instrument malfunction)

• little post-analytical (ex: incorrectly reported)

Kidney function values

• BUN, creatinine, phosphorus

• specifically assess GFR (increased values = decreased GFR)

  • pre-renal: dehydration

  • renal: kidney disease

  • post-renal: ureteral obsruction

BUN

• end-product of protein metabolism

• produced in liver from ammonia, filtered by glomeruli, excreted by kidney

• increased value = decreased GFR

• can occur with liver failure or reduced protein intake

Creatinine

• end-product of muscle metabolism

• filtered by glomeruli, excreted by kidney

• increased value = decreased GFR

• can also occur with decreased muscle mass

Minerals

• phosphorus: primarily intracellular, excreted in urine (or saliva in ruminants)

• calcium: regulated by PTH & calcitriol

Phosphorus

• may be increased due to pre-renal, renal, or post-renal causes along with BUN + Cr

• slightly increased in growing animals

• can see increase or decrease with dietary imbalances

  • increase from vitamin D toxicity

Calcium

• may be elevated due to kidney disease, endocrine diseases, vitamin D toxicity, or neoplasia (most common)

• may be decreased due to low albumin or less common disorders

• ionized = active form

Electrolytes

• sodium: high in extracellular fluid

• potassium: high in intracellular fluids

• chloride: high in extracellular fluid

• bicarbonate: present in both compartments

• tight reference intervals

• maintain electroneutrality in blood/tissue fluids by balancing cations (+) & anions (-)

Sodium

• concentration related to how much water is present is serum relative to solute

• hyper occurs when hypotonic fluid is lost

• hypo can occur with severe diarrhea, ruptured bladder, or endocrine disease

• both changes can cause neuro signs + muscle spasms

Potassium

• excreted by kidney facilitated by aldosterone

• hyper occurs with kidney disease** (decreased excretion), urinary obstruction, bladder rupture; causes cardiac arrhythmia

• hypo occurs with anorexia, increased loss (V/D); causes muscle weakness

Chloride

• follows sodium

• hyper occurs with fluid loss, metabolic acidosis, kidney disease

• hypo occurs with vomiting in small animals, large bowel/cecal diarrhea or excessive sweating in horses, DA in cattle

Bicarbonate

• used as indicator of acid-base status

• low indicates metabolic acidosis, high indicates metabolic alkalosis

Liver functions

• carbohydrate, fat, & protein metabolism

• detoxification & excretion of waste & toxic substances

• production of important clotting factors

Liver enzymes

• hepatocellular injury: increased AST, ALT (leakage enzymes) - only relevant with marked (3x) increase

• cholestasis: increased bilirubin, ALP

• synthetic function: decreased BUN, cholesterol, albumin, glucose (products made by the liver)

ALT

• found primarily in hepatocytes, some in muscle

• useful in small animals, SDH used for large animals

AST

• found in liver, muscle, and RBCs

• not liver specific

• can increase with severe muscle injury or hemolysis

ALP

• usually increased due to increased synthesis & release, associated wth cholestasis or corticosteroids

Cholesterol

• lipid produced in liver as part of lipid metabolism

• decreases occur with some types of liver disease in which liver is not producing normal amounts and in malabsorptive GI disease

• increases occur with endocrine diseases and other diseases

Bilirubin

• waste product of macrophage digestion of RBCs

• conjugated in liver & excreted in bile

• may have pre- (hemolytic anemia), post- (biliary obstruction), or hepatic increases - determined based on history

• increases cause icterus

Total serum protein

• includes albumin + globulin

• slightly lower than plasma protein (clotting factors used up)

• increases with dehydration** (HCT likely also increased), inflammation, or neoplasia

• decreases with decreased production (liver disease) or increased loss (GI/kidney disease)

Albumin

• synthesized by hepatocytes, maintains oncotic pressure of blood

• increases with dehydration

• decreases with liver disease or increased loss (GI/kidney)

Globulin

• synthesized by hepatocytes, includes acute phase reactants, coag factors, carrier proteins, Igs

• increases with dehydration or inflammation

• decreases with liver disease

Glucose

• decrease caused by liver disease

• increase caused by endocrine diseases

Lactate

• by-product of anaerobic metabolism with decreased blood flow/oxygen to the tissues

• increases with low perfusion (shock), hypoxemia, anemia, exercise, liver/kidney disease, etc.

• increased = generally poor prognosis

Muscle enzymes

• CK**

• AST

• occurs with muscle trauma, inflammation, necrosis, exercise, or seizures