copyright 2005,  Welford Medical Computing, Inc.  All rights reserved

RENAL FUNCTION ESTIMATION (User's Manual, pgs. 884-885)

Estimating a patient's renal function is very important in the accurate dosing of medications. Although a 24 hour urine collection for creatinine clearance is one of the most accurate methods for estimating glomerular filtration rate in everyday clinical practice, it is often not available and can be unreliable if the patient is not compliant in performing the test correctly.

Therefore, many formulas have been devised in order to estimate a patient's creatinine clearance based upon the patient's serum creatinine and other variables. Two of the most widely used are:

adult males: ((140-age)*IBW)/ (72 x serum creatinine in mg/dl)

adult females: male formula x 0.85

where IBW (ideal body weight) in kg is:

adult males: 50+(2.3 x (height in inches - 60))

adult females: 45.5 +(2.3 x (height in inches-60))

Note that the Cockroft-Gault equation requires knowing the patient's height to estimate idea body weight, while the MDRD formula requires knowing the whether or not the patient is black. (Both require knowing the patient's age and sex).

You can record the patient's race in the Name Editor starting with version 4.8 (press Name\Edit and choose the Race). The sex and age are recorded there as well.

If you want to use the Cockroft-Gault, equation, you need keep track of patients' heights. To do this, you need to add HEIGHT as the name of a Test in the Lab Book Vocabulary (if you have not already done so). To do that:

1. Press View\Lab Book, choose any patient name, then Utility\Vocabulary.

2. For Test Name, enter HEIGHT.

3. For Numeric, check Yes.

4. For Units, enter either "inches" or "cm". (The Cockroft-Gault equation will work either way; it will automatically convert cm to inches if necessary). Choose whichever units your practice customarily uses in recording patient height.

5. For Category, choose VITAL SIGNS.

6. Press Ok. to store this.

Now, let's record some data and see how the program estimates the patient's creatinine clearance:

1. Press Name\Add.

2. Enter a new patient with Last Name of UREMIA and first name of FRED.

3. Enter a birthdate of 1/1/1940, sex of M. You can leave the Race Unspecified (which means the patient is not Black). Press Ok to store this information.

4. Press View\Lab Book, then use Fred Uremia as the patient.

5. Press Add to add lab results.

6. Use today's date. For Test, enter HEIGHT. For Result, enter 72 inches. Press Ok to store it.

7. Enter today's date. For Test, enter CREATININE. For Result, enter 1.8 mg/dl. Press Ok to store it.

8. Enter a Date of 6-1-2005. For Test enter CREATININE CLEARANCE. For Result, enter 50 ml/min. Press Ok to store it.

9. Once you have recorded the relevant information in the patient's Lab Book and Name Editor, then you can see the most recent estimated and measured creatinine clearance by pressing View\Creatinine Clearance.

Note that the report gives 3 items:

Usually the 3 readings will be close to each other, but since the equations rely on different variables, they will not be in complete agreement every time.

You can jump to this report from various locations in the program, such as the Main Menu, the Prescription Writer, the Prescription Log, the Medication Editor\Add window, etc.

We have already started work on version 4.9, and have lots of exciting new features planned for it. If you have any suggestions for new features, please let us know. We love the feedback!