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By Richard Schamp, MD
CEO, Capstone Performance Systems
Nephropathy refers to any disease of the kidney. In common clinical parlance, the term is modified by an etiology referring to one of over a dozen types, such as analgesic nephropathy, gouty nephropathy or most commonly, diabetic nephropathy. Chronic Kidney Disease (CKD) is defined by GFR (Glomerular Filtration Rate) less than 60 ml/min per 1.73 m2 and/or kidney damage for three or more months. The presence of albuminuria is most commonly used to define kidney damage.
CKD is a progressive condition that can result in significant morbidity and mortality. The condition is common in the elderly — nearly 50% of individuals over 70 years old meet the definition of CKD and most of these have CKD3 or CKD4. Patients with HTN, DM, and family history of kidney failure are at a higher risk for developing CKD and should be monitored closely. However, many cases of CKD in the elderly manifest without a clear cause. Complications of CKD can include cardiovascular disease, anemia, bone disease, electrolyte abnormalities, and uremia. We recommend that primary care providers proactively identify and manage early stage CKD to reduce the risk of disease progression and associated complications.
Establishing a diagnosis
All that is needed to determine a nephropathy diagnosis is to establish kidney disease or damage and its cause, if known. Chronicity is not an issue for this diagnosis. Kidney damage can be defined as structural or functional abnormalities of the kidney, evidenced by markers such as microalbuminuria, polycystic kidneys, hydronephrosis, kidney size, cortical thickness, etc. Albuminuria is a definable marker of kidney damage and can be measured with a spot urine check. Levels of >30 mg/dl (Alb/Cr ratio) are significant for clinical albuminuria.
To establish a diagnosis of CKD:
1. Determine the presence of kidney damage (i.e. nephropathy) AND document its persistence for >3 mo.
2. Determine the level of kidney function (estimated GFR) is <60 ml/min per 1.73 m2 for >3mo.
For CKD to exist, the kidney abnormalities must be chronic, as evidenced by repeated findings over time. An eGFR < 60 represents a loss of at least half of the normal function of the kidneys, and is presumed to represent kidney damage. Therefore, all individuals with an eGFR <60 mL/min/1.73 m2 for ≥3 months are considered CKD with or without other known kidney damage.
Kidney function is determined by the GFR or Glomerular Filtration Rate. GFR is usually estimated using equations that include a filtration marker, such as serum creatinine. The estimated GFR (known as eGFR) uses one of several standard formulas. Most commercial and hospital laboratories use the MDRD (Modified Diet in Renal Disease) equation, as this formula requires only age, gender, and other factors readily available to the lab. However, the MDRD formula is less accurate in settings of extreme age and body size; severe malnutrition or obesity; diseases of skeletal muscle; paraplegia and quadriplegia; vegetarian diet; and rapidly changing kidney function. Experts now determine eGFR with the CKD-EPI Creatinine Equation. Both CKD-EPI and MDRD have been shown to be more accurate than the Cockcroft Gault formula, which is no longer recommended for routine clinical use, but might be used in the old-old with low BMI.
Once a diagnosis of CKD is established, then it should be staged, based upon the eGFR. Staging CKD assists in clinical management, including risk stratification for disease progression and development of complications. Refer to the table (right), showing each stage of CKD and its corresponding description. As noted in the table, for CKD stages 1 and 2, there must be other evidence of renal disease to properly diagnose CKD, thus supporting the need to first identify if kidney damage exists. If the eGFR is between 90 and 60, and no evidence of kidney disease or damage exists, the condition is known as “decreased GFR.”
The eGFR, and thus the CKD stage, may fluctuate and require changes of stages, either up or down. The diagnosis of stage is whatever the eGFR is at the time of assessment.
Coding for Nephropathy and Chronic Kidney Disease
Once a diagnosis of Nephropathy or CKD has been made and staged, it may be coded. Descriptions and corresponding ICD-10 codes of the proper coding for CKD are noted in the table to the right.
Providers should consider linking the nephropathy or CKD to other medical conditions such as hypertension (ICD-10: I12.0, I12.9, I13.0, I13.10, I13.11, I13.2), diabetic nephropathy (E10.21 – type 1 DM, E10.21 – type 2 DM), diabetes with CKD (E10.22 – type 1 DM, E11.22 – type 2 DM) and anemia (D63.1) as appropriate. When present, Kidney Transplant Status (Z94.0) should be recorded in addition to other renal disease diagnoses.
The key to proper diagnosis and coding of nephropathy and CKD is to first establish presence of kidney damage, confirm its chronicity, assess the eGFR with CKD-EPI and document your findings clearly. A splendid CKD Model Practice for PACE providers is available on the NPA members-only website. Non-PACE providers may contact the National PACE Association to request a copy.