Lab test discussion

OVERVIEW
In internal medicine, laboratory tests are important diagnostic tools. The following information is to help you understand what some of the more common tests are and what an abnormal result might mean. Obviously, this section is no substitute for asking questions and discussing things during an appointment with your physician, but we thought this would be helpful for the time in between visits to our office. Some abnormal lab results need attention right away, some are of importance but don't need to be addressed immediately, and some are of trivial, if any, significance. In general, the physicians of Colorado Springs Internal Medicine will prioritize how abnormal lab results are addressed. Significant abnormalities that need immediate attention will generally prompt a phone call to you and may require an office visit right away or, rarely, an admission to the hospital. Other abnormalities might require some additional lab testing or an additional office visit in the near future. Mild abnormalities that may be of little importance can simply be discussed at your next regularly scheduled office visit.

SPECIFIC LAB TESTS

CBC (complete blood count) Includes WBC (white blood cell count), Hgb (hemoglobin), Hct (hematocrit), Plt Ct (platelet count), MCV (mean corpuscular volume), the breakdown of white cell types (neutrophil, lymphocyte, monocyte, eosinophil, basophil), and some other numbers. Discussed below.

WBC (white cell count)
White blood cells fight infection. Different types of white cells have different functions. An elevated white count most often is a sign of an infection. A mildly elevated white count can be seen with minor infections and even with noninfectious causes such as significant pain or very severe stress. An elevated white count can sometimes be due to a bone marrow problem such as lymphoma. Corticosteroids such as predisone will raise the white cell count. A low white cell count sometimes is an indication of a bone marrow problem but sometimes is normal for a given person.

Hbg (hemoglobin) and Hct (hematocrit)
These are measures of the amount of red blood cells and oxygen carrying capacity of the blood. If these are low, that is what defines anemia. Anemia can be due to many different causes. If these are high, that can be a sign of a low blood oxygen level, such as with certain chronic lung or heart diseases.

Plt Ct (platelet count)
Platelets are small cell fragments that help the blood clot. A number of conditions can cause a low platelet count. A low platelet count can make bleeding more likely. In general, the platelet count needs to be around 20,000 or lower before the risk of serious spontaneous bleeding increases.

BMP (basic metabolic profile) (BUN, creatinine, glucose, sodium, potassium, CO2, chloride, calcium)

Creatinine
This is a marker of kidney function. An increased number means decreased kidney filtration rate. A tremendous number of medical conditions and medications can cause this to rise. A mild elevation that is new, such as to 2.0, may require attention in the next few weeks, but is generally not cause for alarm. Patients with whom kidney specialists are starting to discuss the possibility of kidney dialysis generally have creatinine levels approaching 4.0.

BUN (blood urea nitrogen)
This is related to kidney function as well. The ratio of BUN/creatinine gives some indication of how well hydrated the person is. A ratio of about 20 or greater suggests someone is a bit dehydrated. This can be common in a dry climate like Colorado, in patients on certain medications such as diuretics (water pills), or simply from fasting overnight for lab work.

eGFR (estimated glomerular filtration rate) (synonymous with "creatinine clearance")
This is another estimate of kidney filtration rate and is calculated based on the creatinine, a patient's age, gender, and race.

Glucose
This is the form of sugar the body uses for energy. An elevated glucose is what is seen with diabetes. Fasting glucose should be less than 100. Fasting glucose between 100 and 125 is termed "prediabetes". Fasting glucose greater than 125 on more than one occasion diagnoses diabetes.

Sodium
Otherwise called, in lay terms, salt. High sodium level can be seen with dehydration, usually fairly significant dehydration. A low sodium level usually reflects a condition where the body retains too much fluid such as congestive heart failure or liver disease. It also can be seen in people taking diuretics (water pills), and when people have had significant vomiting and/or diarrhea. A low sodium level does NOT mean sodium deficiency and does NOT mean that you should eat more sodium. It means your body is hanging on to relatively more water than sodium.

Potassium
An electrolyte that is important in maintaining normal heart rhythm and in helping muscles function normally. A potassium level that is excessively low or even excessively high can cause certain heart rhythm abnormalities, sometimes dangerous. Certain water pills can lower the potassium level, a couple of less commonly used water pills can raise it. Impaired kidney function can raise it. In general, a potassium level may need urgent attention, such as an emergency room visit or hospital admission, if it is less than 2.6 or greater than 6.5.

CO2 (or bicarbonate)
This is useful as a rough measure of the acidity of someone's blood. It is most useful or most often paid attention to, in patients who are critically ill and requiring hospital admission for things like severe infection, heart attacks, etc.

Chloride
Rarely looked at with any importance by itself. Tends to move in parallel with the sodium. Abnormalities usually direct attention toward other electrolyte abnormalities.

Calcium
A measure of calcium concentration in the blood. A very low or very high level can cause weakness. The result on a blood panel is NOT a reflection of things like calcium concentration in the bones and generally has little, if any, relationship to the amount of calcium one consumes in their diet.

LIPID PROFILE (cholesterol profile) (total cholesterol, triglycerides, HDL, LDL)

LDL
This is the "bad" cholesterol and probably the most important component of the lipid profile. An elevated LDL increases the risk of heart disease and arterial disease elsewhere. An LDL less than 100 is ideal. Depending on how many other cardiac risk factors a person has, medication might be recommended to lower the LDL if it is greater than 100, 130, 160, or 190.

HDL
This is the "good" cholesterol. An elevated HDL has some protective benefit against arterial disease, in the heart and elsewhere. A low HDL increases the risk of arterial disease. In general, an HDL higher than 50 is desirable. It is difficult to raise a low HDL. Regular exercise can raise it. Modest alcohol consumption can raise it. Smoking often lowers the HDL so quitting smoking might raise it.

Triglycerides
Another type of fat in the bloodstream. Elevated triglycerides are risk factor for arterial disease, though not as strong a risk factor as is an elevated LDL. Usually an elevated triglyceride level does not occur alone, but is accompanied by a low HDL and is also very common with diabetes.

Total cholesterol
This used to be the initial screening test for cholesterol levels but now that complete cholesterol profiles are done, is of much less importance, relative to the LDL, HDL, and triglycerides. In fact, the total cholesterol is simply a combination of the specific components of the cholesterol profile. Roughly speaking, the total cholesterol is equal to the LDL plus the HDL plus one-fifth of the triglycerides [Total chol= LDL+HDL+(TG/5)] though this equation does not work if the triglyceride level is too high.

THYROID TESTS (TSH, free T3, free T4)
TSH (thyroid stimulating hormone)
This is the "barometer" that we use to assess thyroid function. It goes in the opposite direction of thyroid hormone levels. A low TSH is seen when the thyroid is overactive and makes too much thyroid hormone (hyperthyroidism). A high TSH is seen when the thyroid is underactive and makes too little thyroid hormone (hypothyroidism).

Free T3 and free T4
These are direct measures of thyroid hormone levels. The TSH is the gold standard for assessing thyroid gland function. Thus, free T3 and free T4 are usually unnecessary.

HEPATIC FUNCTION (liver tests) (protein, albumin, total and indirect bilirubin, ALT, AST, alk phos)
These measure various aspects of liver function and can tell us about liver disease.

Protein and albumin
The liver produces a tremendous amount of different proteins. A low protein and/or low albumin level can be a sign of malnutrition but also can be low simply with an acute illness, like pneumonia, kidney infection, stomach flu, etc.

Bilirubin, ALT (sometimes called SGPT), AST (sometimes called SGOT), alk phos (alkaline phosphatase)
These are tests that tell us about liver function, liver injury, and/or obstruction in the bile ducts draining secretions from the liver into the intestine. There are many conditions that can raise these.

Hemoglobin A1C (HgbA1C)
A form of hemoglobin (a protein) that has glucose attached to it. Everybody has hemoglobin A1C in their bloodstream. In people with diabetes or even prediabetes, the hemoglobin A1C level will be higher than normal. How high it is reflects how high, on the average, someone's blood glucose (blood sugar) has been over the last three months. In general, diabetics should have this test at least twice a year, sometimes even quarterly, to monitor their blood sugar control.

PSA (prostate specific antigen)
This protein is made by prostate tissue. All men have PSA in their bloodstream. In the early 1990s, this test started being widely used to screen for asymptomatic prostate cancer. This was done despite the complete lack of any evidence that screening for prostate cancer by checking a PSA prevents prostate cancer deaths. PSA screening remains controversial. In fact, there is still no compelling evidence that PSA screening prevents prostate cancer deaths. Two very large studies of screening versus no screening showed no benefit in one and minimal benefit in the other, with the latter showing that 1400 men would have to be screened for about a decade and 47 of them would have to undergo treatment for prostate cancer, to prevent one prostate cancer death. What we do know is that treatment for prostate cancer, be it major surgery to remove all the prostate gland, or external beam radiation, or implantable radioactive seeds, all carry risk of things like incontinence of urine, impotence, heart attack during the operative and postoperative period, etc.

Uric acid
Measured if we suspect gout. An elevated uric acid level makes gout more likely but does not by itself diagnose gout. Many people with an elevated uric acid level never develop gout, and a small percent of people with gout will not have an elevated uric acid level.

Amylase, lipase
These are enzymes made in the pancreas and will typically be elevated in conditions like pancreatitis, where there is inflammation of the pancreas. They are most commonly checked when someone has severe, acute abdominal pain with nausea and vomiting.

CRP (C-reactive protein)
This is a nonspecific marker of inflammation. It is most often checked during a work up for various inflammatory conditions, such as bone infection or an autoimmune disease like rheumatoid arthritis. It has also become somewhat popular as a marker for increased risk for coronary artery disease. Higher CRP level is associated with an increased risk of coronary artery disease, but exactly what to do with an elevated CRP in the context of cardiac risk is unclear. There's no "treatment" for an elevated CRP. It's not clear what it means, other than there may be some very low level inflammatory condition, that is not defined and cannot be tested for, that increases the risk for coronary disease. Thus, perhaps its only utility with regard to reducing heart disease risk might be helping to decide whether or not to treat a borderline high cholesterol level with medication.