How to Interpret Your Blood Tests

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How to interpret your blood test results

Review your lab test results

Overview Glucose Electrolytes Waste Products Enzymes

Proteins Blood Fats Minerals Thyroid Glycohemoglobin

CBC Risk Factors Urinalysis

Overview

Laboratory tests are tools helpful in evaluating the health status of an

individual. It is important to realize that laboratory results may be outside of

the so-called " normal range " for many reasons. These variations may be due to

such things as race, dietetic preference, age, sex, menstrual cycle, degree of

physical activity, problems with collection and/or handling of the specimen,

non-prescription drugs (aspirin, cold medications, vitamins, etc.), prescription

drugs, alcohol intake and a number of non-illness-related factors, Any unusual

or abnormal results should be discussed with your physician. It is not possible

to diagnose or treat any disease or problem with this blood test alone. It can,

however, help you to learn more about your body and detect potential problems in

early stages when treatment or changes in personal habits can be most effective.

Our lab, like almost all labs, sets the normal result range for a particular

test so that 95% of our healthy patients fall within the normal range. That

means that 5% of our healthy patients fall outside of the normal range, even

when there is nothing wrong with them. Thus an abnormal test does not

necessarily mean that there is something wrong with you. Statistically if you

have 20 or 30 individual tests run as part of a panel, chances are 1 or 2 will

be slightly outside the normal range. Part of what you see your doctor for is to

interpret whether or not these changes are significant.

This review is a brief summary and is not intended to be comprehensive or

replace discussion of your results with your health care team.

Glucose: This is a measure of the sugar level in your blood. High values are

associated with eating before the test, and diabetes.

The normal range for a fasting glucose is 60 -99 mg/dl. According the the 2003

ADA criteria, diabetes is diagnosed with a *fasting* plasma glucose of 126 or

more. A precursor, Impaired Fasting Glucose (IFG) is defined as reading of

fasting glucose levels of 100 - 125. Sometimes a glucose tolerance test, which

involves giving you a sugary drink followed by several blood glucose tests, is

necessary to properly sort out normal from IFG from diabetes.

Be aware that variations in lab normals exist. Also, Europeans tend to use a 2

hour after eating definition of diabetes rather than a fasting glucose. Using

the European standards tends to increase the number of people who are classified

as having diabetes.

Electrolytes: These are your potassium, sodium, chloride, and CO2 levels.

Potassium is controlled very carefully by the kidneys. It is important for the

proper functioning of the nerves and muscles, particularly the heart. Any value

outside the expected range, high or low, requires medical evaluation. This is

especially important if you are taking a diuretic (water pill) or heart pill

(Digitalis, Lanoxin, etc.).

Sodium is also regulated by the kidneys and adrenal glands. There are numerous

causes of high and low sodium levels, but the most common causes of low sodium

are diuretic usage, diabetes drugs like chlorpropamide, and excessive water

intake in patients with heart or liver disease.

CO2 reflects the acid status of your blood. Low CO2 levels can be due to either

to increased acidity from uncontrolled diabetes, kidney disease, metabolic

disorders, or low CO2 can be due to chronic hyperventilation.

Waste products:

Blood Urea Nitrogen (BUN) is a waste product produced in the liver and excreted

by the kidneys. High values may mean that the kidneys are not working as well as

they should. BUN is also affected by high protein diets and/or strenuous

exercise which raise levels, and by pregnancy which lowers it.

Creatinine is a waste product largely from muscle breakdown. High values,

especially with high BUN levels, may indicate problems with the kidneys..

Uric Acid is normally excreted in urine. High values are associated with gout,

arthritis, kidney problems and the use of some diuretics.

Enzymes

AST, ALT, SGOT, SGPT, and GGT and Alkaline Phosphatase are abbreviations for

proteins called enzymes which help all the chemical activities within cells to

take place. Injury to cells release these enzymes into the blood. They are found

in muscles, the liver and heart. Damage from alcohol and a number of diseases

are reflected in high values.

Alkaline phosphatase is an enzyme found primarily in bones and the liver.

Expected values are higher for those who are growing (children and pregnant

women) or when damage to bones or liver has occurred or with gallstones. Low

values are probably not significant.

GGT is also elevated in liver disease, particularly with obstruction of bile

ducts. Unlike the alkaline phosphatase it is not elevated with bone growth or

damage.

AST/SGOT , ALT/ SGPT are also liver and muscle enzymes. They may be elevated

from liver problems, hepatitis, excess alcohol ingestion, muscle injury and

recent heart attack.

LDH is the enzyme present in all the cells in the body. Anything which damages

cells, including blood drawing itself, will raise amounts in the blood. If blood

is not processed promptly and properly, high levels may occur. If all values

except LDH are within expected ranges, it is probably a processing error and

does not require further evaluation.

Bilirubin: is a pigment removed from the blood by the liver. Low values are of

no concern. If slightly elevated above the expected ranges, but with all other

enzymes (LDH, GOT, GPT, GGT) within expected values, it is probably a condition

known as Gilbert's syndrome and is not significant

CPK is an enzyme which is very useful for diagnosing diseases of the heart and

skeletal muscle. This enzyme is the first to be elevated after a heart attack (3

to 4 hours). If CPK is high in the absence of heart muscle injury, this is a

strong indication of skeletal muscle disease.

Proteins

Albumin and Globulin measure the amount and type of protein in your blood. They

are a general index of overall health and nutrition. Globulin is the " antibody "

protein important for fighting disease.

A/G Ratio is the mathematical relationship between the above.

Blood Fats

Cholesterol is a fat-like substance in the blood which, if elevated has been

associated with heart disease.

Total Cholesterol: A high cholesterol in the blood is a major risk factor for

heart and blood vessel disease. Cholesterol in itself is not all bad, in fact,

our bodies need a certain amount of this substance to function properly.

However, when the level gets too high, vascular disease can result. A total

cholesterol of less than 200, and an LDL Cholesterol of 100 or less is

considered optimal by the National Heart, Lung, and Blood Institute. The levels

that your doctor will recommend depend upon whether you are at high risk for

cardiovascular disease.

As the level of blood cholesterol increases, so does the possibility of plugging

the arteries due to cholesterol plaque build-up. Such a disease process is

called " hardening of the arteries " or atherosclerosis. When the arteries feeding

the heart become plugged, a heart attack may occur. If the arteries that go to

the brain are affected, then the result is a stroke.

There are three major kinds of cholesterol, High Density Lipoprotein (HDL) , Low

Density Lipoprotein (LDL), and Very Low Density Lipoprotein (VLDL).

LDL Cholesterol is considered " bad cholesterol " because cholesterol deposits

form in the arteries when LDL levels are high. An LDL level of less than 130 is

recommended, 100 is optimal, values greater than 160 are considered high risk

and should be followed up by your physician. Those persons who have established

coronary or vascular disease may be instructed by their doctor to get their LDL

Cholesterol well below 100. You should ask your doctor which LDL target he or

she wants for you. There are two ways to report LDL. The most common is simply

an estimate calculated from the Total Cholesterol, HDL, and triglycerides

results. This may say " LDL Calc " . A directly measured LDL Cholesterol is

usually more accurate, but more expensive and may require that your doctor

specify the direct LDL.

HDL cholesterol is a 'good cholesterol' as it protects against heart disease by

helping remove excess cholesterol deposited in the arteries. High levels seem to

be associated with low incidence of coronary heart disease.

Triglyceride is fat in the blood which, if elevated, has been associated with

heart disease, especially if over 500 mg. High triglycerides are also associated

with pancreatitis. Triglyceride levels over 150 mg/dl may be associated with

problems other than heart disease. Ways to lower triglycerides: 1) weight

reduction, if overweight; 2) reduce animal fats in the diet: eat more fish; 3)

take certain medications your physician can prescribe; 4) get regular aerobic

exercise; 5) decrease alcohol and sugar consumption-alcohol and sugar are not

fats, but the body can convert them into fats then dump those fats into your

blood stream 6) restrict calories - carbohydrates are converted to triglycerides

when eaten to excess.

VLDL (very low density lipoprotein) is another carrier of fat in the blood.

Cardiac Risk Factors

C Reactive Protein (CRP): This is a marker for inflammation. Traditionally it

has been used to assess inflammation in response to infection. However we use a

highly sensitive C Reactive Protein which is useful in predicting vascular

disease, heart attack or stroke.. The best treatment for a high C reactive

protein level has not yet been defined, however statin drugs, niacin, weight

loss, quitting smoking, and exercise all appear to improve C- Reactive Protein

Homocysteine: Homocysteine is an amino acid that is normally found in small

amounts in the blood. Higher levels are associated with increased risk of heart

attack and other vascular diseases. Homocysteine levels may be high due to a

deficiency of folic acid or Vitamin B12, due to heredity, older age, kidney

disease, or certain medications. Men tend to have higher levels. Our lab normals

are 4 - 15 micromole/l , but if you have had previous vascular disease we may

recommend medications to reduce it below 10. You can reduce your homocysteine

level by eating more green leafy vegetables and fortified grain products or

cereals. The usual treatment is folic acid with or without Vitamin B-12.

Lipoprotein (a) or Lp(a) : Elevated lipoprotein(a) (Lp[a]) concentrations are

associated with premature coronary heart disease (CHD). The exact mechanism is

not yet clear, but it appears that there is a strong genetic component to

elevated Lp(a) levels that correlates with coronary disease. Persons with

diabetes and a high Lp(a) level appear to be at increased risk of asymptomatic

coronary disease.

Note that a few insurance companies refuse to pay for cardiac risk factor

testing. As of this writing, Aetna stands out as a company that refuses to cover

testing for homocysteine or Lp(a) on the basis that it is " experimental " or

" investigational " . We have asked for a comprehensive review of their policy

since it deviates from the norm.

Minerals

Calcium is controlled in the blood by the parathyroid glands and the kidneys.

Calcium is found mostly in bone and is important for proper blood clotting,

nerve, and cell activity. An elevated calcium can be due to medications such as

thiazide type diuretics, inherited disorders of calcium handling in the kidneys,

or excess parathyroid gland activity or vitamin D. Low calcium can be due to

certain metabolic disorders such as insufficient parathyroid hormone; or drugs

like Fosamax or furosemide type diuretics.

Calcium is bound to albumin in the blood, so a low albumin level will cause the

total calcium level in the blood to drop. You doctor can easily determine if

this is significant or not.

Phosphorus is also largely stored in the bone. It is regulated by the kidneys,

and high levels may be due to kidney disease. When low levels are seen with high

calcium levels it suggests parathyroid disease, however there are other causes.

A low phosphorus, in combination with a high calcium, may suggest an overactive

parathyroid gland.

Thyroid

There are 2 types of thyroid hormones easily measurable in the blood, thyroxine

(T4) and triiodothyronine (T3). For technical reasons, it is easier and less

expensive to measure the T4 level, so T3 is usually not measured on screening

tests.

Please be clear on which test you are looking at. We continue to see a

tremendous amount of confusion among doctors, nurses, lab techs, and patients on

which test is which. In particular, the " Total T3 " , " Free T3 " and " T3 Uptake

tests " are very confusing, and are not the same test.

Thyroxine (T4) . This shows the total amount of the T4. High levels may be due

to hyperthyroidism, however technical artifact occurs when estrogen levels are

higher from pregnancy, birth control pills or estrogen replacement therapy. A

Free T4 (see below) can avoid this interference.

T3 Resin Uptake or Thyroid Uptake. This is a test that confuses doctors, nurses,

and patients. First, this is not a thyroid test, but a test on the proteins that

carry thyroid around in your blood stream. Not only that, a high test number may

indicate a low level of the protein! The method of reporting varies from lab to

lab. The proper use of the test is to compute the free thyroxine index.

Free Thyroxine Index (FTI or T7) : A mathematical computation allows the lab to

estimate the free thyroxine index from the T4 and T3 Uptake tests. The results

tell us how much thyroid hormone is free in the blood stream to work on the

body. Unlike the T4 alone, it is not affected by estrogen levels.

Free T4 : This test directly measures the free T4 in the blood rather than

estimating it like the FTI. It is a more reliable , but a little more expensive

test. Some labs now do the Free T4 routinely rather than the Total T4.

Total T3: This is usually not ordered as a screening test, but rather when

thyroid disease is being evaluated. T3 is the more potent and shorter lived

version of thyroid hormone. Some people with high thyroid levels secrete more T3

than T4. In these (overactive) hyperthyroid cases the T4 can be normal, the T3

high, and the TSH low. The Total T3 reports the total amount of T3 in the

bloodstream, including T3 bound to carrier proteins plus freely circulating T3.

Free T3: This test measures only the portion of thyroid hormone T3 that is

" free " , that is, not bound to carrier proteins.

Thyroid Stimulating Hormone (TSH) : This protein hormone is secreted by the

pituitary gland and regulates the thyroid gland. A high level suggests your

thyroid is underactive, and a low level suggests your thyroid is overactive.

Glycohemoglobin (Hemoglobin A1 or A1c, HbA1c) : Glycohemoglobin measures the

amount of glucose chemically attached to your red blood cells. Since blood cells

live about 3 months, it tells us your average glucose for the last 6 - 8 weeks.

A high level suggests poor diabetes control. Standardization for glycohemoglobin

from lab to lab is poor, and you cannot compare a test from different labs

unless you can verify the technique for measuring glycohemoglobin is the same.

The only exception is if your lab is standardized to the national DCCT

referenced method. You can ask your lab if they use a DCCT referenced method.

FYI, at Amarillo Medical Specialists we do use a test method that is DCCT

referenced.

Hormones

Insulin : Insulin is secreted by the pancreas in response to eating or elevated

blood sugar. It is deficient in persons with type 1 diabetes, and present at

insufficient levels in persons with type 2 diabetes. The natural evolution of

type 2 diabetes causes insulin levels to fall from high levels to low levels

over a course of years. Thus insulin levels in persons with type 1 and type 2

diabetes overlap significantly, and insulin levels are not very useful in

determining type 1 vs type 2. Insulin levels vary widely from person to person

depending upon an individuals insulin sensitivity (or conversely, their insulin

resistance.) Insulin levels also vary widely according to when the last meal

occurred. Insulin resistance is a risk factor for coronary disease, thus

assessing an individual's insulin resistance may have some value using the

HOMA-IR calculation. Insulin levels are also elevated in patients with true

hypoglycemia, however the interpretation of these levels is difficult. Insulin

levels, when measured by itself at a random time is rarely useful.

C-peptide : This is a fragment cleaved off of the precursor of insulin

(pro-insulin) when insulin is manufactured in the pancreas. C-peptide levels

usually correlate with the insulin levels, except when people take insulin

injections. When a patient is hypoglycemic, this test may be useful to determine

whether high insulin levels are due to excessive pancreatic release of insulin,

or from an injection of insulin.

Estradiol : This is the most commonly measured type of estrogen measured. In

women it varies according to their age, and whether they are having normal

menstrual cycles. Hormone levels are also changed when taking birth control

pills or estrogen replacement.

Complete Blood Count (CBC)

The CBC typically has several parameters that are created from an automated cell

counter. These are the most relevant:

White Blood Count (WBC) is the number of white cells. High WBC can be a sign of

infection. WBC is also increased in certain types of leukemia. Low white counts

can be a sign of bone marrow diseases or an enlarged spleen. Low WBC is also

found in HIV infection in some cases. (ed. note: The vast majority of low WBC

counts in our population is NOT HIV related.)

Hemoglobin (Hgb) and Hematocrit (Hct) : The hemoglobin is the amount of oxygen

carrying protein contained within the red blood cells. The hematocrit is the

percentage of the blood volume occupied by red blood cells. In most labs the Hgb

is actually measured, while the Hct is computed using the RBC measurement and

the MCV measurement. Thus purists prefer to use the Hgb measurement as more

reliable. Low Hgb or Hct suggest an anemia. Anemia can be due to nutritional

deficiencies, blood loss, destruction of blood cells internally, or failure to

produce blood in the bone marrow. High Hgb can occur due to lung disease, living

at high altitude, or excessive bone marrow production of blood cells.

Mean Corpuscular Volume (MCV) - This helps diagnose a cause of an anemia. Low

values suggest iron deficiency, high values suggest either deficiencies of B12

or Folate, ineffective production in the bone marrow, or recent blood loss with

replacement by newer (and larger) cells from the bone marrow.

Platelet Count (PLT) : This is the number of cells that plug up holes in your

blood vessels and prevent bleeding. High values can occur with bleeding,

cigarette smoking or excess production by the bone marrow. Low values can occur

from premature destruction states such as Immune Thrombocytopenia (ITP), acute

blood loss, drug effects (such as heparin) , infections with sepsis, entrapment

of platelets in an enlarged spleen, or bone marrow failure from diseases such as

myelofibrosis or leukemia. Low platelets also can occur from clumping of the

platelets in a lavender colored tube. You may need to repeat the test with a

green top tube in that case.

Urinalysis

Urine tests are typically evaluated with a reagent strip that is briefly dipped

into your urine sample. The technician reads the colors of each test and

compares them with a reference chart. These tests are semi-quantitative; there

can be some variation from one sample to another on how the tests are scored.

pH : This is a measure of acidity for your urine.

Specific Gravity (SG) : This measures how dilute your urine is. Water would have

a SG of 1.000 . Most urine is around 1.010, but it can vary greatly depending

on when you drank fluids last, or if you are dehydrated.

Glucose: Normally there is no glucose in urine. A positive glucose occurs in

diabetes. There are a small number of people that have glucose in their urine

with normal blood glucose levels, however any glucose in the urine would raise

the possibility of diabetes or glucose intolerance.

Protein: Normally there is no protein detectable on a urinalysis strip. Protein

can indicate kidney damage, blood in the urine, or an infection. Up to 10% of

children can have protein in their urine. Certain diseases require the use of a

special, more sensitive (and more expensive) test for protein called a

microalbumin test. A microalbumin test is very useful in screening for early

damage to the kidneys from diabetes, for instance.

Blood: Normally there is no blood in the urine. Blood can indicate an infection,

kidney stones, trauma, or bleeding from a bladder or kidney tumor. The

technician may indicate whether it is hemolyzed (dissolved blood) or

non-hemolyzed (intact red blood cells). Rarely, muscle injury can cause

myoglobin to appear in the urine which also causes the reagent pad to falsely

indicate blood.

Bilirubin: Normally there is no bilirubin or urobilinogen in the urine. These

are pigments that are cleared by the liver. In liver or gallbladder disease they

may appear in the urine as well.

Nitrate: Normally negative, this usually indicates a urinary tract infection.

Leukocyte esterase: Normally negative. Leukocytes are the white blood cells (or

pus cells). This looks for white blood cells by reacting with an enzyme in the

white cells. White blood cells in the urine suggests a urinary tract infection.

Sediment: Here the lab tech looks under a microscope at a portion of your urine

that has been spun in a centrifuge. Items such as mucous and squamous cells are

commonly seen. Abnormal findings would include more than 0-2 red blood cells,

more than 0-2 white blood cells, crystals, casts , renal tubular cells or

bacteria. (Bacteria can be present if there was contamination at the time of

collection.)

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