Understanding GFR in CKD and Coding it's stage in 2021

In simple term Glomerular filtration is the first step of filtering excess fluid and waste product from the blood to produce urine. This process is carried out by the glomerulus which is a component of nephron. Each kidney contains over one million of nephrons with glomerulus.

Each nephron contains Bowman's capsule(glomerular capsule), a small blood vessel that brings in unfiltered blood, a tubule that caries away filtered waste materials in the urine, and a small blood vessel that returns filtered blood to the body.

Surprisingly, every minute a healthy heart pumps 5 liters of blood during rest and out of this volume of blood 20% blood which is 1 liter enters in to the kidney for filtration. From this process humans produce 1-2 liters of urine per day. So any disruptions to this filtration can result in to kidney disease. This can be measured by glomerular filtration rate (GFR).

What Is GFR?

The volume of filtrate formed by both kidneys per minute is termed the glomerular filtration rate (GFR). Filtrate is produced by the glomerulus when the hydrostatic pressure produced by the heart transfers water and solutes through the filtration membrane.

GFR is the best way to measure impairment level of kidney function and determine stage of kidney disease. A GFR below 90 mL/min/1.73m2 indicates that your kidney may not functioning properly. Normal GFR level deceases with increase of age. There are 7 stages of chronic kidney disease based on GFR values. It is calculated based on blood creatinine level, age, race, gender, and other contributing factors like weight and height. See below GFR values against diagnosis of CKD stage.

ICD 10 Coding for CKD stage

CKD is defined by the National Kidney Foundation as either kidney damage or a glomerular filtration rate (GFR) less than 60 mL/min/1.73 m2 for three months or more. As we have seen CKD stage diagnosed based on GFR rate, now we will see how we can code CKD. I will not mention any CKD combination code guidelines here. We will go straight to CKD stage codes.

As we know we have 6 codes for CKD stage 1 to stage 5 and ESRD. But from 2021 CMS and NCHS provided changes to CKD stage code with revision to CKD stage 3 and added 3 new codes in contrast to 1 code we were used so far for stage 3. Till 2020 we used to code for 6 CKD stages with 7 ICD codes.

From 2021 with change we have total 9 ICD codes for 7 CKD stages.

Coding Tips

• Do not select your CKD code based on GFR value.

• CKD value is meant for diagnosis of CKD stage by healthcare providers, not for code assignment.

• There is no official direction from regulatory bodies to assign ICD code based on GFR value.

• CKD must be documented by the provider in order to be coded.

• But you should always check GFR value to query physician if you think there is discrepancy in documentation.

• Keep in mind that sometime low GFR value is not due CKD but due other reason like AKI which can be corrected with hydration, So do not unnecessarily query physician.

NOTE: When querying physicians to ask them for the stage, you should provide all the information related to various stages and it's coding requirement and not just diagnosis and the list of stages. “All doctors may not know how the stages to be documented in relation with GFR value, so this will help them to give you the correct answer for your query.