The day I was diagnosed, my doctor handed me a glucometer, an 1800-calorie diabetic diet and a handful of prescriptions, mumbling something about being sorry and I should watch after my health better. WHAT!!! I had been on every low-fat diet and was down to eating like an anorexic bird. The injustice of whole thing was just WRONG.

Over years, as other fatties joined food addiction support groups, shamefully admitting to secret outings to fast food drive-up windows in middle of night and weekends spent with cartons of Haggendaz, I was frigging STARVING!!!

The 1800 calorie diet was AWFUL. I was constantly hungry. The medicine made me run to bathroom every hour, leaving me even hungrier. I was dizzy from blood pressure medicine and tips of my fingers were bruised and tender from blood sugar checks. This was not way I wanted to live. I now understood why my mother seemed so resigned in end to inevitable death. Having diabetes was no fun.

Most people are aware, for example, that several medications taken together can sometimes cause harmful interactions. Most also know that drug allergies can pose significant hazards. (These are topics of other articles in this series). And, many people know that young children, elderly adults, pregnant women, nursing women, and severely debilitated people may all be at higher risk for adverse drug events.

But what most people don’t know is that a simple blood test can be one of most important pieces of information in determining correct dose of many medications…and results of that test are almost never available to your pharmacist, especially if your pharmacist fills your prescription in a retail drugstore. (And, that’s a bummer.)

The test I’m talking about, of course, is “serum creatinine test” (“SEAR-‘em cree-AT-tuh-neen tehst”. It’s a difficult name to pronounce and a difficult test to understand…but one that you need to know about if you or loved ones are taking over-the-counter or prescription medications.)

A serum creatinine test gives a physician or pharmacist an estimate of kidney function.

Serum creatinine is “bean counter” of modern medicine…letting folks know if beans (the kidneys) are working as well as they should.

Why is that important?

Well, kidney function is extremely important in determining correct doses of many medications since kidneys (along with liver) assist in removal of medications from body.

Almost all medications (and/or their chemical by-products) are either removed by liver, by kidneys, or, in many cases, by both kidneys and liver working together.

So, simply put, when beans are not working well, many medications will accumulate in body and increase risk of drug side effects. And that’s an even bigger bummer. (The same is true for liver problems, and we will talk about that in another article in this series.)

As a result, patients with reduced kidney function often need LOWER doses of many medications.

So how does this all work?

Well, creatinine is a chemical that occurs and circulates naturally in human body. It is result of normal protein break-down. And, like many medications, creatinine is normally removed from blood by beans. So, when kidneys are not working well, level of creatinine circulating in bloodstream will start to go up…just like blood level of many medications.

Physicians and pharmacists are routinely and easily able to determine how much creatinine is in blood with results of a serum creatinine test. (This test is part of a very common panel of blood tests. And, if serum creatinine is high, many drugs need to have a lower dose.) The normal value for serum creatinine is about 0.4 to 1.5 mg/dl…but that can vary a bit from lab to lab. So remember: “kidneys no work…serum creatinine go UP”.

Now, serum creatinine is not best measure of kidney function (there are other tests that are much more accurate), but results of serum creatinine test are usually most readily available…and cheapest…and are generally accurate enough for most purposes…so serum creatinine is de facto standard for estimating kidney function…most of time. The gold standard test that doctors use for measuring kidney function is called "creatinine clearance" (cree-AT-tuh-neeeen CLEAR-uhhh-nce) However, not many patients get this particular test because it is pretty darn inconvenient…and smelly. You have to collect all of your urine for 24 hours and keep it in fridge. Not a lot of volunteers for this test….

Creatinine clearance is volume of blood that kidneys clear of creatinine in a given amount of time (and it is usually reported as milliliters per minute).

So, when kidney function decreases, creatinine clearance (the amount of blood that kidneys are successfully “cleaning”) also decreases.

So remember: “kidneys no work…creatinine clearance go DOWN”. (Note: this is easy to remember because it is exact opposite of what you were initially thinking, and opposite of what happens with serum creatinine. Most of medicine is like this.)

Now for super tricky part just for those gunning for an A. There is a way to “guestimate” creatinine clearance using serum creatinine…isn’t that neat. And, that’s probably best way to determine renal function if a measured creatinine clearance is not available.

What you do is run serum creatinine value through a fancy equation that will give you an estimated creatinine clearance, which is itself an estimate of kidney function. (Estimates of estimates of estimates…that’s kind of exacting science I live for.)