Evaluation and Staging of Chronic Kidney Disease

Diagnosis and Staging of Chronic Kidney Disease Introduction Chronic kidney disease (CKD) is diagnosed and monitored using two key measurements: how well the kidneys filter blood (estimated glomerular filtration rate or eGFR) and whether proteins are leaking into the urine (albuminuria). Understanding how to diagnose and stage CKD is essential because it determines patient management and prognosis. The staging system helps clinicians predict kidney function decline and decide when to initiate specific treatments like dialysis. What Defines Abnormal Kidney Function? A person has abnormal kidney function (and thus CKD) if they meet either of these criteria: eGFR less than 60 mL/min/1.73 m² — This indicates the kidneys are filtering blood at less than 60% of normal capacity. Persistent albuminuria — This means the albumin-to-creatinine ratio (ACR) is ≥ 30 mg/g in a urine sample, indicating protein is leaking into the urine. An important point: either one of these findings, if confirmed on repeat testing, is sufficient to diagnose CKD. You don't need both to be abnormal. Screening Recommendations Not everyone needs screening for CKD, but people with risk factors should be tested. Screening is recommended for individuals with: Hypertension (high blood pressure) Diabetes mellitus Marked obesity Age greater than 60 years African ancestry Personal history of kidney disease Family history of kidney disease requiring dialysis The screening tests themselves are simple: Calculate eGFR from a serum creatinine measurement Measure urine albumin-to-creatinine ratio (ACR) on a first-morning urine sample First-morning urine is preferred because it is more concentrated and gives more reliable results than random urine samples. Laboratory Tests for Diagnosis Serum Creatinine and eGFR Serum creatinine is a waste product produced by muscles at a relatively constant rate. The kidneys filter it out, so blood creatinine levels reflect how well the kidneys are working. Higher serum creatinine indicates lower glomerular filtration. Rather than reporting creatinine alone, clinicians estimate the glomerular filtration rate (eGFR) using the serum creatinine value along with age, sex, and race in a mathematical formula. This gives a better sense of kidney function than creatinine alone. Urine Dipstick Testing A urine dipstick is a quick screening test that detects: Hematuria (blood in urine) Proteinuria (protein in urine, primarily larger proteins) If the dipstick shows protein, a more specific urine ACR measurement should follow to detect smaller amounts of albumin. Additional Blood Tests Depending on the stage of CKD and patient needs, additional tests may include: Hemoglobin (to assess for anemia, common in CKD) Potassium (kidneys regulate potassium; it can accumulate in advanced CKD) Phosphate (kidneys regulate phosphate; abnormal levels affect bone health) Parathyroid hormone (PTH — rises in response to kidney disease-related mineral changes) Imaging Studies: Kidney Ultrasound Kidney ultrasound is useful for assessing the structure of the kidneys. In chronic kidney disease, the ultrasound may show: Increased cortical echogenicity (the kidney tissue appears brighter and more textured) Reduced kidney size (kidneys shrink as they lose function) Cortical thinning (the outer layer of the kidney becomes thinner) These findings together suggest chronic kidney disease rather than acute kidney injury (where kidney structure initially appears normal). The CKD Staging System: Five Stages Based on GFR and Albuminuria CKD is staged from 1 to 5 based primarily on eGFR, with albuminuria as an important modifier. Understanding these stages is crucial because each stage carries different clinical implications. Stage 1: Kidney Damage with Normal or High GFR eGFR ≥ 90 mL/min/1.73 m² (normal kidney function) BUT persistent albuminuria is present The key here is that kidney function tests appear normal, but albuminuria indicates kidney disease is present. This might occur in early diabetes before significant function loss. Stage 2: Mild Decrease in GFR with Kidney Damage eGFR 60–89 mL/min/1.73 m² (mild decrease in function) With evidence of kidney damage (usually albuminuria) Kidney function is still mostly preserved, but there is clear evidence of kidney disease. Stage 3: Moderate Decrease in GFR eGFR 30–59 mL/min/1.73 m² This stage is further divided into two substages because the clinical significance changes within this range: Stage 3A: eGFR 45–59 mL/min/1.73 m² (mild-to-moderate decrease) Stage 3B: eGFR 30–44 mL/min/1.73 m² (moderate-to-severe decrease) This subdivision matters because patients in stage 3B require closer monitoring and may need to start planning for renal replacement therapy sooner. This is a detail students often overlook but is important for staging correctly. Stage 4: Severe Decrease in GFR eGFR 15–29 mL/min/1.73 m² At this stage, kidneys retain only 15-29% of normal function. Patients need to begin preparation for renal replacement therapy (dialysis or transplantation). Complications of kidney disease become more apparent, and medications may be needed to manage blood pressure, anemia, and mineral abnormalities. Stage 5: Kidney Failure (End-Stage) eGFR < 15 mL/min/1.73 m² The kidneys retain less than 15% of normal function. Renal replacement therapy is required for survival (dialysis or kidney transplantation). Without treatment, uremia (buildup of waste products) becomes life-threatening. Important Note on Albuminuria and Staging While GFR determines the numeric stage (1-5), albuminuria provides critical additional information about prognosis. Patients with albuminuria at any GFR level tend to have worse outcomes than those without albuminuria at the same GFR. This is why both measurements together give the complete clinical picture.