I didn't think about kidneys until my dad's GP calculated his cardiovascular risk.
I'd written about his cholesterol in the cholesterol article, his HbA1c in the HbA1c article, and his overall cardiovascular picture in the heart health article. When his GP sat down to run the AusCVDRisk calculator (the tool that estimates five-year heart attack and stroke risk), she needed several inputs: age, sex, blood pressure, cholesterol, smoking status, diabetes status, and kidney function.
Kidney function. Right there in the cardiovascular risk equation. And I'd never given it a second thought.
His eGFR was 72 mL/min/1.73m². Normal for his age. No concern. But the GP explained that kidney function is checked because chronic kidney disease is both a cause and a consequence of cardiovascular disease, and because it modifies how aggressively other risk factors need to be managed.
That conversation made me realise that kidneys are the organ nobody thinks about until something goes seriously wrong. They don't get the attention that hearts, livers, and thyroids get. There's no kidney awareness month that most Australians could name. There's no cultural conversation about kidney health the way there is about cholesterol or blood sugar.
And yet, approximately 1.7 million Australian adults (about 11% of the adult population) have biomedical signs of chronic kidney disease. Only about 6% of them know it. The vast majority are walking around with measurably compromised kidney function and no idea, because CKD is silent. No symptoms until it's advanced. No pain. No warning. Just a number on a blood test that most people have never asked about.
A note before we get into it
General information only. I'm not a nephrologist. Kidney disease management involves specialist care, medication adjustment, and dietary guidance that go beyond what blood results alone can provide.
If you have known kidney disease, diabetes, hypertension, or are taking medications that affect the kidneys, work with your GP or specialist for monitoring guidance.
What your kidneys actually do
Your kidneys are filtration plants, processing about 180 litres of blood every day and producing about 1 to 2 litres of urine. They filter waste products, regulate fluid balance, maintain electrolyte levels (sodium, potassium, calcium, phosphate), produce hormones that regulate blood pressure and red blood cell production, and activate vitamin D.
When kidney function declines, waste products accumulate in the blood, fluid balance is disrupted, blood pressure regulation is impaired, and the risk of cardiovascular events increases independently of other risk factors.
Here's the thing: kidney function declines gradually, and the kidneys compensate remarkably well. You can lose a significant proportion of function before any symptoms appear. By the time symptoms show up (fatigue, swelling, changes in urination, nausea), the damage is usually advanced.
This is why blood testing matters. eGFR and creatinine are the early warning system. They detect declining function years before symptoms do.
The tests: eGFR and creatinine
Creatinine
What it measures
Creatinine is a waste product generated by normal muscle metabolism. Your kidneys filter creatinine from the blood and excrete it in urine. When kidney function declines, creatinine accumulates in the blood, so a rising serum creatinine can indicate reduced kidney filtration.
The catch
A creatinine level that looks "normal" in one person might actually represent reduced kidney function in another. Creatinine production varies with muscle mass, age, and sex. A muscular 30-year-old and a slight 75-year-old can have the same creatinine level but very different kidney function. That's why creatinine alone isn't enough.
eGFR (Estimated Glomerular Filtration Rate)
What it tells you
eGFR is calculated from your creatinine level, adjusted for age and sex. It estimates how efficiently your kidneys are filtering blood, expressed as millilitres per minute per 1.73m² of body surface area.
Why it matters more than creatinine alone
eGFR adjusts for the variables that make creatinine unreliable on its own and provides a more standardised assessment. Australian pathology labs use the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation to calculate eGFR. It's automatically reported whenever creatinine is measured, so you don't need to order it separately.
Test it with Bloody Good:
Product: eGFR Blood Test
CKD stages: what the numbers mean
Chronic kidney disease is staged by eGFR. Here's what the stages mean in practical terms.
| eGFR Range | Stage | What it means |
|---|---|---|
| Above 90 | 1 | Normal kidney function. If there's no albuminuria (protein in urine), essentially healthy kidneys. |
| 60–89 | 2 | Mildly reduced. Often normal for age, especially in older adults. Most people have no symptoms and no clinical concern. |
| 45–59 | 3a | Mildly to moderately reduced. Usually when CKD is first identified on blood work. Most people remain asymptomatic. Monitoring frequency increases. |
| 30–44 | 3b | Moderately to severely reduced. Kidney function is measurably compromised. Medication doses may need adjustment. Nephrologist referral often considered. |
| 15–29 | 4 | Severely reduced. Symptoms may begin to appear: fatigue, fluid retention, altered urination. Preparation for potential dialysis or transplant may begin. |
| Below 15 | 5 | Kidney failure. The kidneys can no longer sustain life without dialysis or transplant. |
A single eGFR below 60 doesn't automatically mean CKD. The diagnosis requires sustained reduction (two readings at least 90 days apart) or evidence of kidney damage such as albuminuria or a structural abnormality. A single test is a screening tool. The diagnosis requires confirmation.
Why kidney disease is the condition nobody thinks about
This is the part that I find genuinely alarming.
1.7 million Australian adults have biomedical signs of chronic kidney disease. Approximately 97% of those are in stages 1 to 3, meaning their kidney function is reduced but they're asymptomatic. Only about 6% self-report having the condition. In one large Australian primary care study, only 28% of patients with CKD had the diagnosis recorded in their GP records.
CKD prevalence is increasing. It rose from 4.7% to 6.0% in Western Australia alone over the decade to 2020. It's higher in regional and remote areas, and significantly higher in First Nations communities. Approximately 18% of Aboriginal and Torres Strait Islander adults have biomedical signs of CKD.
When people think about "silent killers" in Australian health, they think about heart disease, diabetes, cancer. Kidney disease rarely makes the list, despite being directly connected to all three.
The cardiovascular connection
This is the link that made me pay attention.
Chronic kidney disease is an independent risk factor for cardiovascular events: heart attack, stroke, heart failure. The relationship is bidirectional. Cardiovascular disease damages kidneys through reduced blood flow and atherosclerosis of renal arteries. Kidney disease accelerates cardiovascular risk through fluid overload, electrolyte imbalance, chronic inflammation, and impaired blood pressure regulation.
The AusCVDRisk calculator includes CKD as a risk-modifying factor because a given cholesterol or blood pressure level carries more risk in someone with reduced kidney function than in someone without it. Kidney function isn't just a "kidney test." It's a cardiovascular test.
I covered this connection in the heart health article. If you read that one and skipped over the kidney section, go back. It matters more than most people realise.
Risk factors for kidney disease
Diabetes. The single largest cause of CKD in Australia. High blood sugar damages the small blood vessels in the kidneys over time. If you have diabetes or pre-diabetes, kidney monitoring should be part of your routine care. See the HbA1c article.
Hypertension. High blood pressure damages kidney blood vessels and is both a cause and a consequence of CKD. Blood pressure management is central to slowing CKD progression.
Age. Kidney function naturally declines with age. After 40, eGFR decreases by approximately 1 mL/min/year. An eGFR of 65 in a 75-year-old may be age-appropriate. The same number in a 35-year-old warrants investigation.
Family history. CKD has a genetic component. First-degree relatives of people with kidney disease are at higher risk.
Obesity. Associated with kidney damage through its links to diabetes, hypertension, and direct effects on kidney tissue.
Smoking. Accelerates CKD progression and compounds cardiovascular risk.
Aboriginal and Torres Strait Islander heritage. Prevalence is approximately 1.5 times the non-Indigenous rate, with higher rates of progression to kidney failure.
Cardiovascular disease. As noted above, the relationship is bidirectional.
Medications that affect kidneys
Several common medications can affect kidney function. This doesn't mean you should stop taking them. It does mean kidney monitoring matters if you're on them long-term.
NSAIDs (ibuprofen, naproxen, diclofenac). Regular use can reduce kidney blood flow and impair function. Occasional use in healthy individuals is generally fine, but long-term use warrants kidney monitoring.
Metformin. The first-line diabetes medication is cleared by the kidneys. Dose adjustment is required as eGFR declines, and it's typically discontinued below eGFR 30.
ACE inhibitors and ARBs (blood pressure medications). These actually protect kidneys in the long term, but can cause an initial dip in eGFR when started. Monitoring after initiation is standard.
Proton pump inhibitors (PPIs). Long-term use has been associated with increased CKD risk in some studies, though the evidence is still evolving.
Lithium. Used for bipolar disorder. Requires regular kidney function monitoring.
Contrast dye. Used in some CT scans and imaging. Can temporarily affect kidney function, especially in people with pre-existing CKD.
Who should be testing
Everyone over 45 should have eGFR checked as part of routine health screening. It's included in the AusCVDRisk assessment.
Aboriginal and Torres Strait Islander peoples from age 18, given the significantly higher prevalence.
Anyone with diabetes or pre-diabetes. Annual kidney function monitoring is standard.
Anyone with hypertension. Kidney function and blood pressure are tightly linked.
Anyone with cardiovascular disease. Kidney function modifies cardiovascular risk management.
Anyone taking medications that affect kidneys (NSAIDs regularly, metformin, lithium, ACE inhibitors/ARBs).
Anyone with a family history of kidney disease.
Anyone who's never had eGFR checked and is over 35. A baseline establishes your starting point.
How to prepare
No specific fasting required for eGFR/creatinine alone. However, if your panel includes other tests (lipids, glucose), fasting is recommended.
Stay normally hydrated. Dehydration can temporarily elevate creatinine.
Avoid heavy exercise for 24 hours. Intense exercise can transiently raise creatinine due to muscle breakdown.
Continue medications unless told otherwise. If you're on ACE inhibitors, ARBs, or other kidney-relevant medications, your GP wants to see kidney function while you're taking them.
Mention all supplements. Creatine supplements (common in gym-goers) can elevate creatinine and confuse the result. Let your clinician know.
Tests to consider through Bloody Good
The kidney function test
eGFR Blood Test — estimated glomerular filtration rate, calculated from creatinine. This is the core marker for kidney function screening.
Metabolic and cardiovascular context
Kidney health doesn't exist in isolation. These markers help your GP interpret eGFR within the broader picture.
HbA1c — diabetes is the leading cause of CKD
Cholesterol (Lipid Studies inc. HDL) — cardiovascular risk management
Fasting Glucose — metabolic screening
Full Blood Count (FBC) — anaemia is common in CKD
High-Sensitivity CRP — inflammation
Calcium Blood Test — kidneys regulate calcium; CKD disrupts this
Comprehensive coverage
The Bloody Good Test includes eGFR alongside 100 biomarkers covering metabolic, cardiovascular, liver, thyroid, nutritional, and inflammatory markers. For adults over 40, this is the most efficient way to assess kidney function within the full health context.
For age-specific testing guidance, see the blood tests by age guide.
What to do after testing
eGFR above 60, no albuminuria: Normal. Retest every 1 to 2 years as part of routine health monitoring. More frequently if risk factors are present.
eGFR 45–59 (Stage 3a): Discuss with your GP. This often reflects age-related decline and may not indicate progressive disease, but it warrants monitoring every 6 to 12 months and attention to cardiovascular risk management. A medication review is appropriate, especially for NSAIDs.
eGFR 30–44 (Stage 3b): More significant. Your GP will likely increase monitoring frequency, review all medications, and may refer to a nephrologist. Blood pressure management and diabetes control (if applicable) become critical.
eGFR below 30: Specialist referral to a nephrologist is standard. This level of kidney impairment affects medication dosing, electrolyte balance, and bone health, and may require planning for kidney replacement therapy.
A single low eGFR but you feel fine: Don't panic, but do retest. A single low reading needs confirmation. Dehydration, recent illness, intense exercise, or creatine supplementation can all produce temporarily low eGFR. Confirmation at least 90 days later is required for a CKD diagnosis.
The trajectory matters most. A stable eGFR of 55 in a 70-year-old is very different from a declining eGFR that was 80 two years ago and is now 55. Tracking over time turns a single number into a story, and that story is what guides clinical decisions.
Explore more biomarkers
Browse the Bloody Good Biomarker Directory
General information only. This article is not medical advice and is not a substitute for care from a qualified health professional. If you have concerning symptoms or urgent health issues, seek medical attention promptly.