Low eGFR on Your Blood Test
What a reduced estimated glomerular filtration rate means, CKD stages explained, and why one low result is rarely the whole story — in plain English.
The Quick Answer
eGFR (estimated glomerular filtration rate) measures how well your kidneys filter waste from your blood, expressed as mL per minute per 1.73 m² of body surface area. In Australia, a normal eGFR in a healthy adult is generally above 90 mL/min/1.73m². Values below 60 on two separate occasions at least 3 months apart are required to diagnose chronic kidney disease (CKD).
A single low eGFR is often transient — caused by dehydration, an acute illness, a recent high-protein meal, or medication effects. The trend over time and the urine albumin-to-creatinine ratio (ACR) matter more than any one result. Your GP will almost always repeat the test before drawing conclusions.
What eGFR Actually Measures — and Why It Matters
Each kidney contains roughly one million tiny filtering units called glomeruli. Each glomerulus is a knot of capillaries surrounded by a capsule that acts like a sieve, filtering blood at high pressure. The combined output of all glomeruli is your true GFR. Since measuring GFR directly requires infusing a substance like inulin (impractical outside research), Australian labs estimate it from a standard equation using your serum creatinine, age, and sex.
The most widely used formula in Australia is the CKD-EPI creatinine equation. It performs well for most adults but is less accurate at the extremes of muscle mass — very muscular people may have an underestimated eGFR, while frail elderly people or amputees may have an overestimated one. In these cases, cystatin C (an alternative filtration marker not influenced by muscle mass) gives a more accurate picture.
Importantly, eGFR only measures filtration. It does not capture tubular function (the kidney's ability to concentrate urine, reabsorb nutrients, or regulate acid-base balance). Urine ACR fills this gap by detecting protein leakage, which is a sensitive early sign of glomerular damage that often precedes any fall in eGFR by years.
CKD Stages by eGFR — The KDIGO Framework
Kidney Health Australia and Australian GPs use the international KDIGO (Kidney Disease: Improving Global Outcomes) staging system. Staging combines eGFR category (G1–G5) with urine ACR category (A1–A3) to guide monitoring frequency and management.
eGFR ≥ 90 mL/min/1.73m² — Normal or high
CKD diagnosed only if structural/urinary abnormality present (e.g. proteinuria, haematuria). Treat underlying cause. Annual review.
eGFR 60 – 89 mL/min/1.73m² — Mildly decreased
Often found incidentally. Address risk factors (BP, glucose, smoking). Check urine ACR. Review every 12 months.
eGFR 45 – 59 mL/min/1.73m² — Mild-to-moderate
Assess for CKD complications (anaemia, bone disease). Optimise BP, avoid nephrotoxins. Review every 6–12 months.
eGFR 30 – 44 mL/min/1.73m² — Moderate-to-severe
Consider nephrology referral. Screen for hyperphosphataemia, hyperkalaemia, metabolic acidosis. Review every 3–6 months.
eGFR 15 – 29 mL/min/1.73m² — Severe
Refer to nephrology. Discuss renal replacement therapy planning (dialysis, transplant). Review every 1–3 months.
eGFR < 15 mL/min/1.73m² — Kidney failure
Kidney replacement therapy (dialysis or transplant) likely required. Managed by nephrologist. Some opt for conservative management.
Common Causes of a Low eGFR
Causes range from entirely reversible (dehydration, medications) to progressive chronic conditions. Knowing the cause is essential because it determines treatment.
Chronic kidney disease (diabetic nephropathy)
Most common cause in Australia. Diabetes damages the glomerular filtration units over years. Good glucose and blood pressure control can slow progression significantly.
Hypertensive nephrosclerosis
Long-standing high blood pressure causes scarring of small kidney vessels. Often asymptomatic until eGFR is significantly reduced. BP control is the key treatment.
Dehydration / acute illness
Reduced blood flow to the kidneys lowers eGFR temporarily. Resolves once fluid balance is restored. Always repeat eGFR 3 months after an acute illness before interpreting the result.
Medications (NSAIDs, contrast dye, aminoglycosides)
NSAIDs (ibuprofen, naproxen, diclofenac) reduce renal blood flow acutely and can cause chronic interstitial nephritis with prolonged use. Contrast-induced nephropathy is usually transient.
Glomerulonephritis
Immune-mediated inflammation of the glomeruli. Can be primary (IgA nephropathy — the commonest in Australia) or secondary to lupus, vasculitis, or infections. Usually presents with haematuria and proteinuria.
Polycystic kidney disease (ADPKD)
Autosomal dominant condition causing progressive cyst formation. Often runs in families. Detectable on ultrasound before eGFR falls. A new medication (tolvaptan) can slow progression in selected cases.
Acute kidney injury (AKI)
Rapid decline in kidney function from sepsis, major surgery, severe dehydration, or medication toxicity. Requires hospitalisation if severe. Many patients recover fully; some sustain permanent damage.
Renovascular disease (renal artery stenosis)
Narrowing of the arteries supplying the kidneys, usually from atherosclerosis in older adults. Can cause resistant hypertension and rapid eGFR decline. Diagnosed with Doppler ultrasound or MRA.
Normal ageing
eGFR naturally declines from about 0.5–1 mL/min/1.73m² per year from age 40. An eGFR of 60–75 mL/min/1.73m² in a healthy 70–80-year-old with no proteinuria may not represent disease.
Symptoms of Reduced Kidney Function
CKD is often called a 'silent disease' because symptoms rarely appear until eGFR is well below 30 mL/min/1.73m². This is why blood test screening for high-risk groups is essential.
No symptoms (most common)
CKD G1-G3 is usually completely silent. The kidneys have enormous reserve capacity and most people feel entirely well until eGFR is below 30 mL/min/1.73m².
Fatigue and reduced exercise tolerance
Anaemia of chronic kidney disease (due to reduced erythropoietin) causes tiredness that worsens as eGFR falls below 45 mL/min/1.73m². Often the first symptom patients notice.
Ankle and lower leg swelling (oedema)
Fluid retention from reduced kidney excretion capacity. Can also reflect nephrotic syndrome if protein loss is significant. Typically worsens toward the end of the day.
Hypertension (high blood pressure)
Both a cause and consequence of CKD. The kidneys regulate blood pressure via the renin-angiotensin system. CKD disrupts this, raising BP further and accelerating kidney decline.
Nocturia (waking to urinate at night)
Damaged kidneys lose the ability to concentrate urine overnight. Increased night-time urination is an early functional sign of reduced tubular capacity, even when eGFR is only mildly reduced.
Uraemic symptoms (G4-G5 only)
Nausea, loss of appetite, metallic taste, itchy skin (pruritus), and confusion occur when waste products accumulate. These are late signs indicating kidney failure is approaching.
Breathlessness
Can be caused by fluid overload, anaemia from CKD, or metabolic acidosis (kidney's inability to buffer acid). New breathlessness in a CKD patient needs urgent assessment.
Muscle cramps and restless legs
Electrolyte imbalances — particularly low calcium, low magnesium, and high phosphate — common in G3b-G5 CKD can cause painful cramps and restless legs syndrome.
Red Flags — When to See Your GP Urgently
Most low eGFR results can be investigated at a routine GP appointment. These findings need a call to your GP within days:
eGFR declining rapidly (>5 mL/min/1.73m² in 12 months)
Rapid decline suggests an acute-on-chronic process or an aggressive underlying cause. Requires urgent nephrology referral regardless of the absolute eGFR value.
eGFR below 30 mL/min/1.73m²
CKD G4 — significant kidney impairment requiring nephrology input and discussion of renal replacement therapy planning (dialysis or transplant).
Hyperkalaemia (potassium >5.5 mmol/L) with low eGFR
Dangerous combination that can cause life-threatening cardiac arrhythmias. May require dietary potassium restriction, medication review (ACE inhibitors, ARBs, potassium-sparing diuretics), or emergency treatment.
Visible blood in urine (haematuria) with low eGFR
Suggests glomerulonephritis or other structural kidney pathology until proven otherwise. Needs urgent urine microscopy and nephrology referral — do not attribute to benign causes without workup.
Sudden eGFR drop after starting a new medication
NSAIDs, ACE inhibitors/ARBs, aminoglycosides, and IV contrast can all cause acute kidney injury. Stop the likely offending medication and recheck eGFR within days to weeks.
eGFR below 60 with uncontrolled blood pressure
Hypertension accelerates CKD progression. Target blood pressure in CKD is below 130/80 mmHg (lower if significant proteinuria). Uncontrolled BP in the context of low eGFR requires urgent GP review.
What Your GP Will Do Next — The Workup
Australian GPs follow Kidney Health Australia and RACGP guidelines for investigating a low eGFR. Here is the usual sequence of investigations and what each one looks for.
Repeat eGFR after 3 months
A single low eGFR does not diagnose CKD. Your GP will repeat the result to confirm it is persistently below 60 mL/min/1.73m². Acute or transient causes (illness, dehydration, medications) need to be excluded first.
First-morning urine ACR
Albumin-to-creatinine ratio in a first-void morning urine sample is the most sensitive early marker of kidney damage. Normal is below 3 mg/mmol. Elevated ACR combined with low eGFR confirms CKD and guides staging.
Serum creatinine and cystatin C
eGFR is derived from serum creatinine using the CKD-EPI equation. Cystatin C-based eGFR is more accurate in people with unusual muscle mass (elderly, amputees, bodybuilders). Australian labs increasingly report both.
Electrolytes and bicarbonate
Potassium (hyperkalaemia is a dangerous CKD complication), sodium, bicarbonate (metabolic acidosis), phosphate (rises in G3b-G5), and calcium (can fall in CKD) are all checked. Abnormalities guide management urgency.
Full blood count for anaemia
Renal anaemia from erythropoietin deficiency becomes clinically significant in G3b-G5. Haemoglobin, iron studies, and sometimes ferritin and transferrin saturation are checked to optimise haemoglobin.
Renal ultrasound
Assesses kidney size (small kidneys suggest chronicity), symmetry, echogenicity, cysts, obstruction, and structural abnormalities. Most Australian GPs order an ultrasound at initial CKD evaluation or when the cause is unclear.
Cause-specific investigations
HbA1c and urine glucose (diabetic nephropathy), blood pressure diary (hypertensive nephropathy), ANA/ANCA/anti-GBM/complement (glomerulonephritis), serum protein electrophoresis (myeloma) as clinically indicated.
Nephrology referral criteria
Australian guidelines recommend nephrology referral for eGFR below 30 mL/min/1.73m², rapid decline >5 mL/min in 12 months, ACR above 30 mg/mmol, suspected glomerulonephritis, or uncertainty about diagnosis.
Protecting Your Kidneys — Diet and Lifestyle
Diet modifications become increasingly important as CKD progresses. Always work with your GP or a renal dietitian before making significant dietary changes — what is right for your stage may differ from general healthy eating advice.
Limit sodium to <2g/day
Reduces BP and proteinuriaAvoid processed foods, canned soups, soy sauce. Use herbs and lemon for flavour. Australian DASH diet guidelines apply.
Moderate protein intake (G3b+)
Reduces hyperfiltration injuryTarget ~0.8g/kg/day protein in CKD G3b-G5. Avoid very high-protein diets and protein supplements. Seek renal dietitian advice.
Limit high-potassium foods (G3b+)
Prevents hyperkalaemiaBananas, oranges, potatoes, tomatoes, and legumes are high in potassium. Leaching vegetables (peel, dice, soak, boil in fresh water) reduces potassium by 50-70%.
Limit high-phosphate foods (G3b+)
Prevents renal bone diseasePhosphate additives in processed foods are more dangerous than natural phosphate in whole foods. Avoid cola drinks, processed meats, and fast food.
Plenty of water (unless restricted)
Supports remaining kidney functionMost CKD patients should drink 1.5–2L of water daily. Fluid restriction only applies in G4-G5 with oliguria or oedema — ask your GP or nephrologist.
Mediterranean-style diet
Cardioprotective and kidney-protectiveOlive oil, vegetables, fruit, fish, legumes, and whole grains. Lower in saturated fat and sodium than typical Australian diet. Associated with slower CKD progression.
Related Reading
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This page provides general educational information about low eGFR and chronic kidney disease. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your GP about abnormal blood test results — they have access to your full medical history and can interpret your results in context. SmarterBlood does not provide medical care.