How to Read Kidney Function Tests: eGFR, Creatinine, UACR, UPCR, and CKD Labs Explained
Many people look at only one number on a kidney report: serum creatinine. But kidney function is not a single-number story. To understand chronic kidney disease, we need to look at eGFR, creatinine, UACR, UPCR, potassium, hemoglobin, calcium, phosphorus, PTH, and vitamin D together [1].
What Is Chronic Kidney Disease?
According to KDIGO, chronic kidney disease means abnormalities of kidney structure or function that persist for at least 3 months and have implications for health [1].
A common clinical threshold is eGFR <60 mL/min/1.73 m² for more than 3 months. However, kidney damage may also be present when eGFR is above 60 if albuminuria is persistent [1][2].
1. eGFR: Estimated Glomerular Filtration Rate
eGFR estimates how well the kidneys filter blood. It is calculated from serum creatinine, age, sex, and other variables.
- G1: ≥90
- G2: 60–89
- G3a: 45–59
- G3b: 30–44
- G4: 15–29
- G5: <15
eGFR naturally declines with age. Recent population data show that healthy 80-year-old men may have a median eGFR around 66, and healthy 80-year-old women around 63 mL/min/1.73 m² [3].
2. Creatinine
Creatinine is a waste product from muscle metabolism. It rises when kidney filtration declines, but it is also affected by muscle mass.
This means a muscular person may have a higher creatinine without severe kidney disease, while an older person with low muscle mass may have a “normal” creatinine despite reduced kidney function.
3. UACR: Urine Albumin-to-Creatinine Ratio
UACR is one of the most important markers for early kidney damage, especially in people with diabetes or hypertension.
- A1: <30 mg/g
- A2: 30–300 mg/g
- A3: >300 mg/g
A UACR above 30 mg/g may indicate kidney damage even when eGFR is still above 60 [2].
4. UPCR: Urine Protein-to-Creatinine Ratio
UPCR measures total urine protein. It correlates with 24-hour urine protein collection and is often used as a practical alternative [4].
- Normal: <150 mg/g
- Mild proteinuria: 150–500 mg/g
- Severe proteinuria: >500 mg/g
- Nephrotic-range proteinuria: >3500 mg/g
For CKD screening and prognosis, UACR is generally preferred. UPCR can be used when UACR is unavailable [1][5].
5. Hemoglobin and Ferritin
The kidneys produce erythropoietin, which helps the bone marrow make red blood cells. As CKD progresses, erythropoietin production may fall, leading to renal anemia.
- Anemia in men: hemoglobin <13 g/dL
- Anemia in women: hemoglobin <12 g/dL
KDIGO 2026 continues to use these adult hemoglobin thresholds for anemia in CKD [6].
6. Potassium, Sodium, and Bicarbonate
Potassium is especially important in advanced CKD. High potassium may affect heart rhythm and should be taken seriously.
- Potassium: commonly 3.5–5.0 mEq/L
- Sodium: commonly 135–145 mEq/L
- Bicarbonate: commonly 22–28 mEq/L
Low bicarbonate may suggest metabolic acidosis, which is common in CKD and requires individualized treatment [7].
7. Calcium, Phosphorus, PTH, and Vitamin D
As kidney function declines, phosphorus excretion decreases and active vitamin D production falls. This may lead to abnormal calcium, phosphorus, and PTH levels.
KDIGO CKD-MBD guidance suggests monitoring calcium and phosphorus every 6–12 months in CKD G3, every 3–6 months in G4, and every 1–3 months in G5. PTH monitoring depends on CKD stage and disease progression [8].
8. Albumin and Lipids
Serum albumin may reflect nutrition, inflammation, liver disease, or protein loss in urine. Lipid abnormalities are also common in CKD and contribute to cardiovascular risk.
When Should You Be More Careful?
- Rapid eGFR decline
- UACR >300 mg/g
- UPCR >500 mg/g
- Potassium >5.5 mEq/L
- Hemoglobin clearly reduced, especially <10 g/dL
- Low bicarbonate with worsening kidney function
- High phosphorus or high PTH
Can Traditional Chinese Medicine Help?
In traditional Chinese medicine, CKD care may focus on supporting qi and blood, improving circulation, strengthening spleen and kidney function, and reducing turbidity. Common herbal directions may include Astragalus, Angelica sinensis, Salvia miltiorrhiza, and Rheum officinale.
However, CKD patients should avoid self-medicating with unknown herbs or concentrated extracts. Herbal treatment must consider eGFR, potassium level, edema, anticoagulant use, and current medications.
Conclusion
Kidney function should not be judged by creatinine alone. eGFR tells us about filtration, UACR and UPCR tell us whether the kidney is leaking protein, and electrolytes, hemoglobin, calcium, phosphorus, and PTH show how well the kidneys maintain internal balance.
References
- KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney International. 2024. KDIGO Guideline PDF
- National Kidney Foundation. Urine Albumin-Creatinine Ratio (uACR). NKF
- Age- and sex-specific reference values of estimated glomerular filtration rate for European adults. UK Biobank publication summary. UK Biobank
- Kamińska J, Dymicka-Piekarska V, Tomaszewska J, Matowicka-Karna J, Koper-Lenkiewicz OM. Diagnostic Utility of Protein to Creatinine Ratio in Spot Urine Sample Within Routine Clinical Practice. Critical Reviews in Clinical Laboratory Sciences. 2020.
- Sumida K, Nadkarni GN, Grams ME, et al. Conversion of Urine Protein-Creatinine Ratio or Urine Dipstick Protein to Urine Albumin-Creatinine Ratio for Use in Chronic Kidney Disease Screening and Prognosis. Annals of Internal Medicine. 2020.
- KDIGO 2026 Clinical Practice Guideline for Anemia in Chronic Kidney Disease. KDIGO Anemia Guideline PDF
- Kim HJ. Metabolic Acidosis in Chronic Kidney Disease. Electrolyte Blood Press. 2021. PMC
- KDIGO 2017 Clinical Practice Guideline Update for CKD-MBD. KDIGO CKD-MBD PDF