Thursday, September 19, 2024

A quicker way to estimate the eGFR of CKD-EPIcr-cys.

Estimating kidney function by calculating the estimated glomerular filtration rate (eGFR) is important, and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine-cystatin C equation (CKD-EPIcr-cys) is one of the most accurate ways of estimating eGFR. However, after reviewing thousands of laboratory tests from institutions nationwide, I've seen only ONE lab automatically calculate the eGFR using CKD-EPIcr-cys.

Instead, labs typically calculate eGFR using either the CKD-EPI creatinine equation (CKD-EPIcr) based on serum creatinine or the CKD-EPI cystatin C equation (CKD-EPIcys) based on serum cystatin C. But if you want the more accurate CKD-EPIcr-cys? You're on your own, and you must calculate CKD-EPIcr-cys using a website like the National Kidney Foundation.

A more practical and quicker method to estimate the eGFR of CKD-EPIcr-cys is to average the eGFR values obtained from CKD-EPIcr and CKD-EPIcys. This method is almost as accurate and significantly faster.

Consider an 81-year-old man with a serum creatinine level of 1.6 mg/dL and a serum cystatin C level of 2.2 mg/L.

Using the equations from the NKF website:

  • Using CKD-EPIcr: eGFR = 43 mL/min/1.73 m²
  • Using CKD-EPIcys: eGFR = 25 mL/min/1.73 m²

The estimated eGFR by averaging these values is (43 + 25) / 2 = 34 mL/min/1.73 m².

For comparison, the calculated eGFR using CKD-EPIcr-cys is approximately 33 mL/min/1.73 m², showing a difference of only 1 mL/min/1.73 m².

In this example, the difference in eGFR was only 1. Using the average eGFR of CKD-EPIcr and CKD-EPIcys -- both printed on most lab tests -- is usually an excellent way to estimate the eGFR of CKD-EPIcr-cys.

You can also create a macro to automate the averaging process, reporting the estimated eGFR in patient charts as "eGFR = X (avg. of CKD-EPIcr & CKD-EPIcys)."

Saturday, September 14, 2024

Best Apple AI feature.

“Intelligent Breakthrough & Silencing” is the best feature of Apple Intelligence in iOS 18.1 beta.

How to choose a random Apple Watch face.

Apple Watch tip: you can create up to 50 watch faces (!) and randomly switch between them using this shortcut: https://www.icloud.com/shortcuts/a5a0df6d068444e5b1fe8e926c44fbad. With the Apple Watch Ultra, you can even assign this shortcut to the action button. Great for rediscovering favorite faces.