Understanding kidney function tests

Your lab report shows: Creatinine 1.4 mg/dL, eGFR 52 mL/min/1.73m². Your doctor says "Your kidney function is declining. We need to monitor this closely." You panic. Does this mean you're heading toward dialysis? Is kidney disease already here? What can you do?

Kidney function tests are subtle but critical. Unlike heart disease, which announces itself with a heart attack, or diabetes, which causes obvious weight loss and thirst, kidney disease creeps silently. By the time you feel symptoms, kidneys are often 70-80% damaged already.

This is why understanding your kidney numbers matters enormously. A mildly elevated creatinine today can be caught early, lifestyle changes can slow progression, and you might avoid dialysis entirely. But if you ignore the numbers, kidney disease accelerates and becomes irreversible.

Why kidneys matter: Understanding their job

Your kidneys are your body's filtration system. They filter waste from blood into urine. They also regulate:

  • Blood pressure (through water and salt balance)
  • Red blood cell production (through erythropoietin hormone)
  • Bone health (through vitamin D activation)
  • Electrolytes (potassium, sodium, phosphate)

Kidney disease disrupts all of these functions. That's why chronic kidney disease causes not just uremia (waste buildup) but also anemia, bone disease, high blood pressure, and heart disease.

Stages of kidney disease:

  • Stage 1: eGFR ≥90 (normal kidney function, but may have protein in urine)
  • Stage 2: eGFR 60-89 (mild loss of kidney function)
  • Stage 3a: eGFR 45-59 (moderate loss)
  • Stage 3b: eGFR 30-44 (moderate loss, more risk)
  • Stage 4: eGFR 15-29 (severe loss, prepare for dialysis)
  • Stage 5: eGFR <15 (kidney failure, needs dialysis or transplant)

The four main kidney function tests

Creatinine: The direct measure

Creatinine is a waste product from muscle metabolism. Muscles break down naturally, producing creatinine. Your kidneys filter creatinine out into urine. Healthy kidneys clear it efficiently, so creatinine stays low.

If kidneys aren't working, creatinine accumulates in blood—rising blood creatinine directly reflects falling kidney function.

Normal creatinine: 0.7-1.3 mg/dL (slightly varies by gender and muscle mass)

  • Males typically 0.9-1.3 mg/dL
  • Females typically 0.7-1.1 mg/dL

Prediabetic/at-risk range: 1.1-1.4 mg/dL Early kidney disease: 1.5-2.0 mg/dL Advanced kidney disease: >2.0 mg/dL

Why creatinine alone is incomplete:

Creatinine depends on muscle mass. A 90-year-old grandmother with weak muscles might have creatinine 0.8 mg/dL (looks normal) but actually have significantly reduced kidney function because she has little muscle to produce creatinine. Meanwhile, a bodybuilder with large muscles might have creatinine 1.4 mg/dL but perfectly normal kidney function.

This is why eGFR (estimated glomerular filtration rate) is used instead—it corrects for age, gender, and body size.

eGFR: The adjusted estimate

eGFR is calculated using creatinine, age, gender, and ethnicity. It estimates how many milliliters of blood your kidneys can filter per minute (mL/min/1.73m²—the 1.73m² is standardized body surface area).

Calculation: Most labs use CKDEPI formula: eGFR = 141 × (Cr/0.7 or 0.9)^-0.329 × (0.993)^age × (1.018 if female) × (1.159 if Black)

You don't need to calculate this yourself—labs do it automatically. But understanding that it corrects for your individual factors is important.

Normal eGFR: ≥90 mL/min/1.73m² At-risk range: 60-89 mL/min/1.73m² Early disease: 45-59 mL/min/1.73m² Moderate disease: 30-44 mL/min/1.73m² Advanced disease: 15-29 mL/min/1.73m² Kidney failure: <15 mL/min/1.73m²

Key insight: If your eGFR dropped from 85 to 65 in one year, that's a significant decline and needs investigation. If it stayed stable at 65 for five years, that's reassuring—the decline has plateaued.

Albumin-to-creatinine ratio (ACR): The protein leak

Normally, large proteins stay in blood; only small waste products leak into urine. Damaged kidneys leak protein.

Albumin-to-creatinine ratio measures how much albumin (the main blood protein) appears in urine per unit of creatinine in urine.

Normal ACR: <30 mg/g creatinine **Microalbuminuria (early kidney damage):** 30-300 mg/g **Macroalbuminuria (significant kidney damage):** >300 mg/g

Why this matters:

Someone can have normal eGFR but elevated ACR—meaning kidneys are starting to leak protein before function actually declines. This is the earliest sign of kidney damage, especially in diabetics.

Example: A diabetic person with eGFR 90 (looks normal) but ACR 80 (abnormal) has early diabetic kidney disease that needs treatment before eGFR falls.

BUN (Blood Urea Nitrogen): The complementary measure

BUN is another waste product from protein metabolism. Like creatinine, healthy kidneys filter it efficiently. Kidney disease causes BUN to accumulate.

Normal BUN: 7-20 mg/dL Elevated: >25 mg/dL suggests kidney disease

Important: BUN rises and falls more rapidly than creatinine, so it's less reliable. A person who's dehydrated has high BUN but normal creatinine. A person with kidney disease has both elevated.

BUN-to-creatinine ratio: Normally 10-20. If ratio is high and creatinine is normal, usually means dehydration. If both elevated, suggests kidney disease.

How to read a kidney function report

Most Indian labs report like this:

KIDNEY FUNCTION TEST
Creatinine (Serum)    : 1.2 mg/dL    [Normal: 0.7-1.3]
BUN                   : 24 mg/dL     [Normal: 7-20]
eGFR (calculated)     : 65 mL/min    [≥60 is normal]
Albumin-Creatinine    : 45 mg/g      [Normal: <30]
Potassium             : 4.2 mmol/L   [Normal: 3.5-5.0]
Phosphate             : 3.2 mg/dL    [Normal: 2.5-4.5]

The critical values are eGFR (main marker of function) and ACR (sign of early damage).

Understanding kidney disease progression

How kidney disease develops:

Most chronic kidney disease comes from:

  1. Diabetes (30-40% of kidney disease cases in India)
  2. High blood pressure (30-40%)
  3. Chronic glomerulonephritis (inflammation from immune disease)
  4. Recurrent kidney infections
  5. Polycystic kidney disease (inherited)
  6. Obstructions (kidney stones, tumors)

The process typically follows this pattern:

Year 1-5: Kidney damage is happening, but eGFR still ≥60 (Stage 1-2). Person feels fine. No symptoms.

Year 5-15: eGFR gradually falls from 60 to 45 to 30 (Stage 3-4). Still often asymptomatic, but fatigue, swelling, nausea might start.

Year 15+: eGFR falls below 15 (Stage 5). Kidney failure. Urgent need for dialysis or transplant. Symptoms: severe fatigue, nausea, loss of appetite, swelling, shortness of breath.

Why early detection matters:

If caught in Stage 2-3, interventions can slow decline significantly:

  • Controlling blood sugar (in diabetics) can slow decline by 30-50%
  • Controlling blood pressure (target <130/80) can slow decline by 20-30%
  • ACE inhibitors or ARBs (blood pressure medications) protect kidneys and are recommended even if BP is only mildly elevated
  • Low-salt diet helps
  • Avoiding NSAIDs (paracetamol is safer)
  • Maintaining healthy weight and exercise

If ignored and reaches Stage 5: Only dialysis (3x/week, 4 hours each) or transplant can keep you alive. Cost is enormous, quality of life severely affected.

What declining kidney function looks like

Let's say someone gets their creatinine checked regularly:

Date Creatinine eGFR Status
Jan 2024 1.0 85 Normal
Jul 2024 1.1 75 Normal but declining
Jan 2025 1.3 60 Mild kidney disease (Stage 2)
Jul 2025 1.5 50 Moderate disease (Stage 3a)
Jan 2026 1.8 42 Moderate-severe disease (Stage 3b)

This person is declining about 5-10 mL/min per year. If this rate continues:

  • Will need dialysis in 3-4 years (when eGFR reaches 10-15)
  • Time to start preventive measures NOW

Interventions today (control diabetes, control BP, ACE inhibitor, low-salt diet) might slow decline to 2-3 mL/min per year, delaying dialysis 10+ years or preventing it entirely.

What happens in each stage

Stage 1 (eGFR ≥90):

  • Kidney function normal
  • May have protein in urine (sign of damage even if function intact)
  • Usually no symptoms
  • Action: Annual check if risk factors (diabetes, high BP, family history)

Stage 2 (eGFR 60-89):

  • Mild loss of kidney function
  • Usually no symptoms
  • Action: Annual kidney tests, control risk factors (diabetes, BP, weight), avoid NSAIDs

Stage 3a (eGFR 45-59):

  • Moderate kidney disease
  • Still often asymptomatic, but fatigue starting
  • Action: Kidney tests every 6 months, start nephrology referral, tighter control of diabetes and BP, restrict salt

Stage 3b (eGFR 30-44):

  • Moderate-severe disease
  • Fatigue, swelling, poor appetite may develop
  • Anemia starting, blood pressure medication needed
  • Action: See nephrologist (kidney specialist), kidney tests every 3-4 months, prepare for dialysis option

Stage 4 (eGFR 15-29):

  • Severe kidney disease
  • Symptoms: Fatigue, nausea, loss of appetite, swelling, shortness of breath
  • Anemia significant, bone disease present
  • Action: Monthly nephrologist visits, regular lab tests, start dialysis education, prepare vascular access (fistula surgery)

Stage 5 (eGFR <15):

  • Kidney failure
  • Need dialysis 3x/week or daily peritoneal dialysis, or transplant
  • Life expectancy on dialysis ~10 years

Specific concerns in Indian context

Why kidney disease is common in India:

  1. High diabetes prevalence (10% population) → diabetic kidney disease
  2. High blood pressure prevalence → hypertensive kidney disease
  3. Pollution (air, water) → chronic exposure to toxins
  4. Recurrent kidney infections and dehydration in rural areas
  5. High salt diet

Why screening is critical:

  • Most Indians discover kidney disease only in Stage 4-5
  • By then, >80% kidney function is lost
  • Many avoidable dialysis cases if detected earlier

Recommended screening:

  • Age 45+: Creatinine, eGFR, ACR annually
  • If diabetic: Creatinine, eGFR, ACR every 6-12 months (diabetic kidney disease is main cause)
  • If high BP: Creatinine, eGFR, ACR annually
  • If family history of kidney disease: Start at age 30-40

Common patterns and what they mean

Pattern 1: Stable low eGFR

  • eGFR 50-55 and stays there for years
  • Meaning: Kidney disease present but not progressing
  • Cause often: Childhood kidney disease, single kidney, recovered infection
  • Action: Annual monitoring sufficient

Pattern 2: Slowly declining eGFR

  • eGFR 80 → 75 → 70 → 65 over 2-3 years
  • Meaning: Progressive kidney disease, manageable decline
  • Cause: Usually diabetic or hypertensive disease early-stage
  • Action: Intensive control of risk factors, frequent monitoring

Pattern 3: Rapidly declining eGFR

  • eGFR 85 → 60 → 35 in one year
  • Meaning: Aggressive kidney disease, needs urgent action
  • Causes: Active vasculitis, lupus, new obstruction, acute kidney injury from infection or medication
  • Action: Urgent nephrology referral, possible kidney biopsy, aggressive treatment

Pattern 4: Normal creatinine, elevated ACR

  • Creatinine 0.9, eGFR 95, but ACR 150
  • Meaning: Earliest sign of kidney damage, function not yet declined
  • Cause: Early diabetic or hypertensive kidney disease
  • Action: This is the BEST time to prevent progression. Intensive treatment of diabetes/BP can reverse or stop progression.

Medication impact on kidney function

Several common medicines affect kidneys:

Medicines that injure kidneys (avoid in kidney disease):

  • NSAIDs (ibuprofen, naproxen, diclofenac) → use paracetamol instead
  • ACE inhibitors/ARBs (if eGFR <30, need careful monitoring)
  • Some antibiotics (aminoglycosides, fluoroquinolones in high doses)

Medicines that protect kidneys (recommended in kidney disease):

  • ACE inhibitors (lisinopril, enalapril) if diabetic or proteinuria
  • ARBs (losartan, valsartan) similar protection
  • Beta-blockers and calcium channel blockers for blood pressure

Medicines that need dose adjustment in kidney disease:

  • Metformin (can cause lactic acidosis if eGFR <30)
  • Certain statins
  • Antibiotics

Practical tracking

Create a simple tracking sheet to monitor kidney disease:

KIDNEY FUNCTION TRACKING
Date | Creatinine | eGFR | ACR | BP | Weight | Status
Jan 2026 | 1.2 | 65 | 45 | 140/85 | 75 | Diagnosed stage 3a
Apr 2026 | 1.2 | 65 | 38 | 135/82 | 74 | Stable, BP improving
Jul 2026 | 1.1 | 70 | 28 | 130/78 | 73 | Improving! Likely from medication/diet changes

Track this annually minimum, every 6 months if diagnosed with kidney disease.

FAQ

Q: I have eGFR 55 and my doctor said this is "early kidney disease." Do I need dialysis? A: No. You're in Stage 3a. Dialysis is only considered when eGFR falls below 10-15. You have many years. Focus on controlling risk factors now to slow decline.

Q: Can kidney disease be reversed? A: Not completely, but progression can be slowed dramatically. Early treatment of diabetes, BP control, and medications can slow decline from 10 mL/min per year to 2-3 mL/min per year. Some people never progress to need dialysis if caught early enough.

Q: My creatinine went from 1.0 to 1.3 in one month. Is this kidney disease or measurement error? A: Probably not true decline—creatinine shouldn't drop that fast unless there was acute injury (dehydration, medication, infection). Repeat testing and make sure you're well-hydrated before the repeat test.

Q: What happens after dialysis starts? Can I ever stop? A: Almost never. Once kidneys fail completely (eGFR <10), only dialysis or transplant keeps you alive. The goal is to prevent reaching that point through early treatment.

Q: How often should I test if I have kidney disease? A: eGFR should be checked every 3-6 months if Stage 3-4, annually if Stage 1-2. More frequent if rapidly declining or just starting medication.

Q: What diet should I follow? A: Stage 1-3: Normal diet, but reduce salt (<5g/day), maintain protein intake, lose weight if overweight. Stage 4: May need protein restriction, potassium restriction, phosphate restriction (depends on potassium and phosphate levels). Work with dietician.

Key takeaway

Kidney disease is silent—you might have 50% kidney function loss and feel fine. This is why regular testing matters. If you have diabetes, high blood pressure, or family history of kidney disease, get a kidney function test annually. If you already have early kidney disease (eGFR 45-90), the interventions you start TODAY can determine whether you need dialysis in 5 years or never.

Most people think kidney disease is a death sentence requiring dialysis. The truth: Early detection and aggressive management often prevents reaching that point entirely.

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