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Why we do routine lab testing

Physicians often request laboratory tests to assess for a diagnosis, rule out a certain diagnosis, or to check your health status during a routine physical. Listing every available lab test for all obscure or exotic problems would result in a book, but below are answers to the most commonly asked questions about various tests. Use this as a guide only. With any lab test, there are times when we find trivial or insignificant highs or lows, so be sure to discuss with your doctor about how or if any abnormalities may be important in your case.

Basic Chemistries

The chemistries are often used to evaluate overall health status as well as to help us diagnose various disorders.


Usually performed on a fasting blood specimen, Glucose is a measurement of blood sugar. If it’s elevated at all, we tend to want to repeat the results. An elevation above 140mg/dL on more than one occasion fulfills the American Diabetes Association criterion for a diagnosis of diabetes.

Uric Acid

When elevated, Uric Acid can form crystalline deposits that can cause kidney stones. Uric Acid can also cause deposits in the joints that lead to a form of arthritis called gout. You can have normal Uric Acid levels and still get stones or gouty arthritis.

BUN & Creatinine

Blood Urea Nitrogen (BUN) and Creatinine are waste products that we all make as part of daily metabolic functions. It’s the job of the kidneys to excrete and eliminate these substances. If elevated, BUN and Creatinine suggest impairment of the kidneys. We sometimes also measure the BUN/Creatinine ratio, because if there is elevation of BUN out of proportion to the Creatinine, there may other causes of the elevation.


These are important mineral or trace elements. An elevation or depression of Sodium, Potassium, Chloride, Carbon Dioxide, Calcium, Magnesium or Phosphorus may be the first clue your doctor has to certain metabolic disturbances.

Serum Proteins

The Total Protein, Albumin, Globulin, and A/G ratio are measured levels of proteins. Coupled with some of your other Chemistries, Highs and Lows may be a sign of liver disease or kidney disease. There are also certain diseases in which you make too much protein or in which you body is breaking down proteins it shouldn’t be.

Liver Function Tests (LFT’S)

Bilirubin, with the standard liver function enzymes are a very important reflection of how well your liver is performing as the body’s “oil filter”. All foods, medications, and metabolic wastes are at one time or another filtered through the liver. With almost any medication we prescribe for long-term or maintenance therapy of any condition, we will want to follow you LFT’s at a minimum of once a year.

Cholesterol & Lipoproteins

Lipids in your circulation are well known as sources of atherosclerosis. Of even greater relevance to your future health than a Total Cholesterol is knowledge of the LDL (bad cholesterol), the HDL (good cholesterol) and the Risk Ratios [Chol/HDL or LDL/HDL]. If your values are out of line, you will be given specific information about cholesterol


The serum iron level tells whether or not you have adequate iron in the blood circulation to provide for making healthy Red Blood Corpuscles. A normal iron level generally suggests that you are getting enough iron in the diet, although we also recommend iron replacement if you are found to be anemic on you Complete Blood Count (below)

Complete Blood Count

WBC count

White Blood Corpuscles are the white cells, important for helping our bodies fight infections.

RBC count

Red Blood Corpuscles are the iron-carrying cells which carry oxygen to all tissues of the body within a molecule of Hemoglobin.

Hemoglobin (HgB)

This vital molecule carries iron and oxygen through out your system; deficient levels of HgB mean you are anemic, and there are several forms of anemia which may need to be tested for independently.

Hematocrit (HCT)

This reflects the percentage of our total blood volume which is composed of Red Blood Cells; it too is a parameter of anemia.

Red Cell Indices

MCV,MCH,MCHC, and RDW: These values reflect the relative size of individual red blood corpuscles and the average volume of each cell. They are important any time anemia is diagnosed.

Differential Cell Count

Measurement of the percentage of your White Blood Corpusles (WBC’s) that are Neutrophils, Lymphocytes, etc. This is most meaningful when there are significant abnormalities in you WBC count. Certain WBC’s help you fight bacteria, while others may be elevated during viral infections, during a parasitic illness or if you suffer from allergies.


Various parameters of measurable substances in the urine, together with microscopic analysis of the sediment of your urine, help us determine whether you have a Urinary Tract Infection or a variety of kidney or urinary tract pathologies.

Thyroid Profile

T3, T4, T3 Uptake

These are measurements of components of metabolic thyroid hormones in your bloodstream to look for evidence of hyperthyroidism (too much hormone) or hypothyroidism (not enough hormone). Thyroid conditions are quite common, but because other medical problems often emulate thyroid diseases, it’s important to actually measure these substances directly. Subtle changes may not be significant, and sometimes normal levels are found even in mild cases of hormone depravation.

TSH (Thyroid Stimulating Hormone)

This hormone is secreted by the pituitary gland in the brain in response for the need for more thyroid hormone. TSH is literally the driving force to make the thyroid gland work harder. Thus, TSH is the first and most sensitive indicator for an underproductive thyroid gland, elevation of TSH means you aren’t making enough hormone, so your physician would want to start you on a supplement or increase your current dose if you already take one.


PSA (Prostate Specific Antigen)

Test for all men in whom prostate trouble is a concern, and certainly all men over the age of 50, should have a PSA blood screening annually. Couples with a digital rectal exam of the prostate gland, this test helps us look for evidence of the most common cancer in men today.

Pap Smear

In ladies, a scraping of cells lining the cervix and the vagina, the Pap smear, is crucial to screen for early inflammatory changes of cancer in the female organs. It’s not a perfect test, but, coupled with a routine gynecologic assessment, is our best screen for occult problems. In ladies lacking a womb (i.e., post-hysterectomy), cells from the vaginal mucosa are taken to look for vaginal cancers or inflammation.

Levels of Medications: Many medicines which we use are truly wonder drugs and can save your life. However, we may need to measure the actual level of medication in your bloodstream. Therapeutic Range is a level of medication that is typically regarded as effective for treatment without being at a toxic level. There are times when, if your condition is stable and all else looks favorable, we may just continue your current dosage even if your level is below or above the normal range. Examples of conditions for which we might monitor levels include asthma (theophylline), heart conditions (digitalis or certain rhythm-controlling agents), epilepsy/seizures (dilantin, Phenobarbital, and others), and depressive disorders (nortriptyline, lithium, and others).

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