Blood tests for CKD (creatinine, eGFR, etc.)

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Chronic Kidney Disease (CKD) is a long-term condition characterized by a gradual loss of kidney function over time. Diagnosing and monitoring CKD involves various blood tests that provide critical information about kidney function and overall health. Below is a detailed explanation of the key blood tests commonly used in the diagnosis and monitoring of CKD, including creatinine, eGFR, and other relevant biomarkers.

1. Serum Creatinine

Creatinine is a waste product produced by muscle metabolism and is excreted by the kidneys. The serum creatinine test measures the amount of creatinine in the blood. Elevated levels of serum creatinine indicate impaired kidney function, as the kidneys are less able to clear creatinine from the blood.

Normal Range:
- For men: 0.7 to 1.3 mg/dL
- For women: 0.6 to 1.1 mg/dL
CKD Indication: Higher-than-normal creatinine levels may suggest CKD or acute kidney injury. However, since creatinine levels can be influenced by muscle mass, age, sex, and diet, this test is often used in conjunction with other assessments.

2. Estimated Glomerular Filtration Rate (eGFR)

The eGFR is a calculation based on the serum creatinine level, age, sex, and sometimes race. It provides an estimate of how well the kidneys are filtering blood. The eGFR is a key indicator of kidney function and is used to stage CKD.

eGFR Categories:
- G1: eGFR ≥ 90 mL/min/1.73 m² (Normal or high)
- G2: eGFR 60-89 mL/min/1.73 m² (Mildly decreased)
- G3a: eGFR 45-59 mL/min/1.73 m² (Mild to moderate decrease)
- G3b: eGFR 30-44 mL/min/1.73 m² (Moderate to severe decrease)
- G4: eGFR 15-29 mL/min/1.73 m² (Severely decreased)
- G5: eGFR < 15 mL/min/1.73 m² (Kidney failure)
CKD Indication: An eGFR below 60 mL/min/1.73 m² for more than three months is a sign of CKD. The lower the eGFR, the more severe the kidney damage.

3. Blood Urea Nitrogen (BUN)

BUN measures the amount of urea nitrogen in the blood, a waste product formed from the breakdown of protein. Urea is normally excreted by the kidneys, and an elevated BUN level may indicate reduced kidney function.

Normal Range: 7 to 20 mg/dL
CKD Indication: Increased BUN levels can be a sign of kidney dysfunction, though they can also be affected by factors such as dehydration, high protein intake, or gastrointestinal bleeding.

4. Serum Cystatin C

Cystatin C is another marker of kidney function that can be measured in the blood. It is considered more accurate than creatinine in certain populations, such as the elderly, those with low muscle mass, or those with certain diseases.

Normal Range: Approximately 0.6 to 1.2 mg/L (varies by lab)
CKD Indication: Elevated cystatin C levels suggest impaired kidney function. This test can be used to calculate an alternative eGFR, especially when creatinine-based eGFR is less reliable.

5. Electrolytes and Acid-Base Balance

Blood tests to measure levels of electrolytes such as sodium, potassium, calcium, and bicarbonate are important in assessing kidney function and monitoring CKD. The kidneys help regulate these substances, and imbalances can indicate the progression of CKD.

Key Tests:
- Serum Potassium: High levels (hyperkalemia) may indicate kidney failure.
- Serum Bicarbonate: Low levels may indicate metabolic acidosis, a common complication of CKD.

6. Albumin-to-Creatinine Ratio (ACR)

While this is typically a urine test, it’s closely related to kidney function monitoring. ACR measures the amount of albumin (a type of protein) in the urine compared to creatinine. Increased albumin levels in the urine are an early sign of kidney damage.

Normal Range: < 30 mg/g
CKD Indication: An ACR above 30 mg/g may indicate CKD. Higher levels are associated with a greater risk of kidney disease progression.

7. Hemoglobin and Hematocrit

Anemia is a common complication of CKD due to decreased production of erythropoietin, a hormone produced by the kidneys that stimulates red blood cell production. Blood tests for hemoglobin and hematocrit levels can help monitor anemia in CKD patients.

Normal Hemoglobin:
- Men: 13.8 to 17.2 g/dL
- Women: 12.1 to 15.1 g/dL
CKD Indication: Lower-than-normal levels may indicate anemia, requiring treatment such as iron supplementation or erythropoiesis-stimulating agents.

8. Phosphorus and Parathyroid Hormone (PTH)

CKD can lead to mineral and bone disorders, so monitoring phosphorus and PTH levels is important. The kidneys help regulate phosphorus and activate vitamin D, which is necessary for calcium absorption.

Normal Phosphorus: 2.5 to 4.5 mg/dL
CKD Indication: Elevated phosphorus levels and increased PTH can indicate worsening CKD and bone disease (secondary hyperparathyroidism).

9. Vitamin D Levels

CKD often leads to vitamin D deficiency because the kidneys are less able to convert vitamin D into its active form. Blood tests to measure 25-hydroxyvitamin D levels can guide supplementation and management of CKD-related bone disorders.

Normal Range: 20 to 50 ng/mL
CKD Indication: Low levels may require vitamin D supplementation to prevent complications such as osteomalacia or secondary hyperparathyroidism.

10. Lipid Profile

CKD patients are at higher risk for cardiovascular disease, so regular monitoring of lipid levels (total cholesterol, LDL, HDL, triglycerides) is important.

Normal Ranges:
- Total Cholesterol: < 200 mg/dL
- LDL: < 100 mg/dL
- HDL: > 40 mg/dL
- Triglycerides: < 150 mg/dL
CKD Indication: Abnormal lipid levels may necessitate lifestyle changes or medications to reduce cardiovascular risk.

Conclusion

Blood tests are essential for the diagnosis and monitoring of Chronic Kidney Disease. Regular testing helps track the progression of the disease, adjust treatment plans, and manage complications. By understanding these tests, patients and healthcare providers can work together to optimize care and improve outcomes for those with CKD.