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crash course on Medical Lab tests

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Bonerskinners:
Laboratory exams are requested by your doctor so he could confirm what’s wrong with you.  Knowing these tests would be very helpful for you to understand what you’re doctor is thinking about.

1. Urinalysis - probably one of the most abused tests because it’s cheap.  Coined from “urine analysis“, it can tell your doctor certain things that could be helpful, like if you have a significant amount of pus cells in your urine (plus you have symptoms of difficulty in urinating, fever, chills), you most likely have a urinary tract infection, and you’d probably need antibiotics. Red cells in urine could be anything (think kidney stones, kidney inflammation, menstrual contamination, etc), but if you’re male, it shouldn’t be there.  Proteins (like albumin) and Sugar (Glucose) should never be detected in you’re urine as well.  If you’re diabetic and you have protein in your urine, consult a nephrologist (kidney specialist) right away. It might mean that your Diabetes is destroying your kidneys. Other things the urinalysis could tell you?  Urine pH, specific gravity, urine color, casts.

    Tip : Make sure you “produce” the specimen an hour before you submit it to the lab.  And it should be a mid-stream clean catch, meaning, during specimen collection, clean your privates first then allow some urine to spill before getting the specimen.

2. BUN and Creatinine - BUN stands for Blood Urea nitrogen, and together with creatinine, these two exams could tell if your kidneys are functioning properly.  You don’t want them to be elevated, because elevation almost always means that you have some form of kidney failure (or renal failure).  Your kidneys usually filter out these substances from you’re body, so if your kidneys are busted, your blood levels of these substances would rise.  Simply put- creatinine and BUN reflects the level of crap in your blood that is supposed to be filtered by functioning kidneys. Your doctor could get an idea of why you have renal failure if these two are done (whether it’s due to dehydration, or an intrinsic kidney defect), so it’s best to let him interpret these tests for you.  Some patients with extremely high levels would need dialysis.

    Another thing : You only need one kidney to live, and one kidney could efficiently clear out unwanted toxins from your body.  So if your BUN and creatinine is high, it means that BOTH kidneys are not functioning well.

3. Cultures - anything with the word “culture” means that the doctors would want to know what organism would grow in the specimen (the more common ones are blood, urine, sputum cultures).  This is usually requested so you’re doctor could be guided as to what antibiotic he would give you.  In cultures, you could know and brag about the name of the bacteria that grew in your sample, and what antibiotics would kill it.

    Organisms might not grow in cultures but this doesn’t mean that it’s not there.

4. CBC - Complete Blood Count. This is again, one of the most abused tests.  The CBC could be very informative, and sometimes, it’s so informative that it could confuse your doctor.  Your CBC should indicate at least the following : Hemoglobin, Hematocrit, White Blood Cell Count, Differential Count, Platelet Count. In some laboratories, they don’t include the platelet count, so sometimes the doctor specifies “CBC with PC” in their order.  The hemoglobin and hematocrit (H&H) are parameters for your doctor to know if you have enough red blood cells or not (I’m assuming that you have heard of red blood cells in your biology class.  Yes, it’s that portion of blood that makes it red).  Males have slightly higher values than females.  If this is decreased, you have anemia, and you might need blood transfusion.  Anemia is not a diagnosis itself, but rather a sign of a disease. If you have problems with your H&H, you need to have this investigated further by your doctor (preferably, a blood disease specialist or hematologist).

IWM:
Doc, regarding tests for kidney function, which is more reliable - BUN or creatinine?

Bonerskinners:
Good Question...
strictly speaking Creatinine is a more specific tests for the kidneys

Creatinine is a break-down product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body (depending on muscle mass). Creatinine is chiefly filtered by the kidneys and not reabsorbed in the blood. Hence, Creatinine is used to calculate the filtration rate and the renal clearance.

BUN or blood urea nitrogen measures the amount of nitrogen in the blood in the form of urea. The liver produces urea in our body (via the urea cycle) as a waste product of the digestion of protein. The kidneys in turn remove urea from the blood.
So, simply put, an elevated BUN has a many causes... whether its due to increase formation of your urea or a decrease in excretion via kidneys and other many causes

That's the reason why doctors usually order BOTH BUN and creatinine. The ratio of BUN and creatinine will usually reflect the cause of the renal problem. A high BUN with a normal creatinine will reflect dehydration as a cause. And a high BUN with high creatinine will reflect an intrinsic renal damage.

IWM:
Thank you for that doc. So to sum it up, both tests (BUN and Crea) can be used to test renal function but creatinine is more specific to renal function than BUN.

Bonerskinners:
yup. you got it.  toast::

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