Lab Tests – What Do They Mean?


The tests we discuss below have links to a website that can give you more information than the brief information here; the site also discusses tests not reviewed below, and symptoms that can be associated with the abnormalities. Another source of information about lab tests is at

Liver Tests: (ALT, AST, ALK Phosphatase, Bilirubin)

Alkaline Phosphatase is an enzyme (protein) found in the liver, bone, and intestinal tissues. In the liver, it is mainly located in the ducts (tubes) that run throughout the liver. Some causes of elevated levels include:

  • Medication side effect
  • Anticonvulsant use (phenytoin/Dilantin, Phenobarbital)
  • Alcoholism
  • Diabetes mellitus
  • Liver Disease (especially obstruction of the ducts), including hepatitis, cirrhosis
  • Gallstones
  • Bone Disease, including Paget’s Disease
  • Bone Cancers, pancreas cancer, some blood cancers (multiple myeloma), other cancers
  • Hyperthyroidism, Hyperparathyroidism
  • Lymphoma
  • Leukemia
  • Cancer metastases to the bone
  • Kidney disease, severe
  • Infection of the bone (osteomyelitis)
  • Pregnancy
  • Fractures, extensive, associated with healing
  • Infections involving the liver (tuberculosis, abscess)
  • Mono

Some causes of decreased levels include:

  • Anemia from B-12 deficiency
  • Celiac Disease
  • Hypothyroidism
  • Malnutrition
  • Zinc or Magnesium Deficiency
  • Vitamin D Intoxication

ALT (Alanine Transaminase) is an enzyme found in the liver, pancreas, and skeletal muscle. It acts as a catalyst in the process necessary for amino acid production; the body uses amino acids to make proteins. Some causes of elevated levels include:

  •   Medication effect
  •   Obesity
  •   Liver Disease (obstruction and infection)
  •   Fatty liver (steatosis)
  •   Liver Cancer
  •   Congestive Heart Failure
  •   Reye’s Syndrome
  •   Mononucleosis
  •   Muscular Dystrophy

Some causes of decreased levels include:

  •   Cancer

AST (Aspartate Transaminase) is a catalytic enzyme found in the liver, skeletal muscle, and cardiac tissue. Often both the AST and ALT will be elevated for the same reason. Some causes of elevated levels include:

  • Medication effect
  • Alcoholic hepatitis
  • Liver Disease (including infection, especially hepatitis; cirrhosis)
  • Blockage of the bile drainage, including gall stones in the bile duct
  • Liver Cancer
  • Congestive Heart Failure
  • Myocardial infarction (heart attack)
  • Pancreatitis
  • Stroke
  • Reye’s Syndrome
  • Mononucleosis

Some Causes of decreased levels include:

  • Dialysis

Bilirubin (Total) is produced in the liver, spleen, and bone marrow. It is a by-product of hemoglobin breakdown. Bilirubin is found in direct (conjugated) and indirect (unconjugated) fractions. Some causes of elevated levels include:

  • Hepatitis (viral, alcohol-related, toxin-related, medication-related)
  • False elevation due to medications/chemicals in the blood
  • Inherited (genetic) disorders, such as Dubin-Johnson syndrome, Gilbert’s disease
  • Obstruction of the bile system
  • Cancer
  • Infection (abscess)
  • Anemia, including B12 deficiency and sickle cell anemia
  • Alcoholism
  • Destruction of red blood cells (inherited, severe infections, immune diseases)
  • Mononucleosis
  • Pulmonary Embolism
  • Transfusion Reactions
  • Malaria
  • Toxic Shock Syndrome
  • Certain Medications

Some causes of decreased levels include:

  • Certain Medications (but not considered to be clinically significant)


Cholesterol is a fat. It is found in all body tissues and plays a vital role in cell membranes. Over 90% of the cholesterol in our blood is made in our liver. This cholesterol is made primarily from saturated fats. One type of cholesterol subfraction (LDL) is associated with damage to the inner lining of the blood vessels. Optimally, the total cholesterol should be under 200. More important than the total cholesterol are the subfrations, noted below. Note that low cholesterol is unknown to cause any disease, although it can be seen in some diseases.
Some causes of increased levels include:

  • Genetics (most common cause)
  • Celiac disease
  • Pancreatitis
  • Hypothyroidism
  • Liver/gallbladder disease
  • Kidney failure
  • Certain medications, including beta blockers, contraceptives, anabolic steroids

Some causes of decreased levels include:

  • Acute illness
  • Malnutrition
  • Liver disease
  • Certain cancers
  • Certain medications, especially those used to treat cholesterol

HDL Cholesterol is a protective subfraction of cholesterol. The higher the level, the better.

LDL Cholesterol is a sub fraction of cholesterol associated with heart disease and stroke. There are different cutoffs for “normal”, depending on risk factors for heart disease (like diabetes, high blood pressure, smoking, and more.)

Triglycerides (TG) are a long chained fatty acid. TG are absorbed through the intestines and stored in fat cells. TG are also synthesized in the liver from fatty acids as well as from proteins and glucose above the body’s current needs and then stored in fat cells. The levels vary, and are especially high after a meal. Even levels after fasting can change from day to day.
Some causes of elevated levels include:

  • Alcoholism
  • Diabetes out of control
  • Genetics
  • Pancreatitis
  • Hypothyroidism
  • Renal (kidney) failure

Some causes of decreased levels include:

  • Malabsorption
  • Malnutrition


Potassium is a positively charged cation found mostly inside our cells. It is involved with water balance, ph balance, membrane transplant, and electrical conduction in the muscle and nerve cells. Potassium levels too high or too low may cause problems with our nerves and muscles. Some causes of elevated levels include:

  • Lab error (a common cause, due to red cells “leaking” potassium after they die)
  • High potassium diet (including certain fruits, substitute salt)
  • Renal (kidney) failure
  • Abnormal adrenal gland function (Addisons’s disease and hypoaldosteronism)
  • Muscle injury
  • Dehydration
  • Diabetes
  • Fever
  • Breakdown of red blood cells
  • Lab error (a common cause, due to red cells “leaking” potassium after they die)
  • Diuretics of a certain type (such as triamterene, spironolactone, amiloride)
  • ACE inhibitors (the “prils” – lisinopril, benazepril, captopril, fosinopril and others)
  • ARB’s (the “sartans” –  valsartan, losartan, olmesartan, irbesartan, others)
  • Anti-inflammatories including Advil/ibuprofen, Aleve, many others
  • Beta blockers

Some common causes of decreased levels include:

  • Diuretics of a certain kind, such as furosemide, and HCTZ (hydrochlorothiazide)
  • Diarrhea, vomiting and other causes of dehydration
  • Less common causes of low levels:
  • Abnormal adrenal gland function
  • Renal (kidney) disease
  • Malabsorption
  • Low magnesium
  • Laxatives

Sodium is a positively charged electrolyte found mostly outside cells. It is involved with water balance, pH (acid/base) balance, and nerve and muscle function. It’s found in table salt, but blood levels are not usually related to salt intake.
Some common causes of elevated levels include (almost always due to excess fluid loss):

  • Dehydration
  • Vomiting

Some uncommon causes of high sodium:

  • Abnormal adrenal gland function (Cushing syndrome)
  • Congestive Heart Failure
  • Renal (kidney) failure
  • Too much salt intake with too little water intake
  • Inadequate levels of the hormone ADH
  • Some common causes of decreased levels include:
  • Loss of sodium – diarrhea, excess sweating, diuretics
  • Abnormal adrenal gland function (Addison’s disease)
  • Kidney disease
  • Some less common causes of low sodium:
  • Too much water intake
  • Congestive heart failure
  • Liver failure/cirrhosis
  • Diabetes
  • Thyroid Disease
  • Bowel Obstruction
  • Some brain and lung diseases with abnormal levels of hormone (ADH)


Sedimentation Rate (Sed Rate) is a simple measure of how fast the red blood cells settle down to the bottom of a tube of blood. The cells settle faster when certain proteins are in the serum part of the blood. These proteins are elevated in infection and inflammatory conditions of the body. The elevated level of these proteins increase the sed rate. The sed rate is a very sensitive test, but not very specific. In other words it tells you something is going on, but not what that something is. (A related test is C-Reactive Protein). A normal sed rate, however, does not mean you do not have an inflammatory disease. In other words, a high sed rate is a useful test result; a normal or mildly elevated sed rate is not helpful. Some causes of elevated levels include:

  • Anemia
  • Arthritis
  • Infection
  • Autoimmune diseases like Lupus
  • Specific inflammatory diseases: temporal arteritis and polymyalgia rheumatica
  • Certain cancers, and especially multiple myeloma
  • Allergies
  • Old age
  • Pregnancy
  • Kidney failure
  • Certain medications

Some causes of decreased levels include:

  • Congestive Heart Failure
  • Certain red blood cell diseases, including sickle cell anemia and polycythemia

Mark Smith, MD
Dennis Oliver, MD