Chronic Kidney Disease: Why So Much Function Can Be Lost Before It Shows

CKD often causes no early symptoms, but it is not diagnosed from feeling well or one blood test. Persistent eGFR and urine abnormalities define the condition, while both measurements help estimate future risk.

Chronic kidney disease is defined by persistence Chronic kidney disease, called CKD, means an abnormality of kidney structure or function that persists for more than three months and affects health. CKD can be present because estimated filtration remains below a threshold. It can also be present because urine, imaging or other tests show lasting kidney damage. In adults, an eGFR below 60 must usually appear on at least two tests separated by at least 90 days. A normal or mildly reduced eGFR does not establish CKD by itself. GFR categories G1 and G2 require another persistent marker of kidney damage. The word chronic describes duration. It does not mean that the condition must worsen steadily or inevitably reach kidney failure. Why symptoms can appear late A nephron is a microscopic filtering and processing unit within the kidney. Healthy kidneys contain many nephrons and have substantial capacity for maintaining internal balance. When some nephrons stop working, remaining nephrons can increase their workload. The body can therefore maintain acceptable waste, salt and fluid control despite reduced kidney function. This compensation helps explain why early CKD often causes no symptoms. It does not mean that a fixed percentage of function must disappear before symptoms begin. Symptoms depend on the cause, speed of change and complications. Some kidney diseases cause blood in urine, pain or swelling before eGFR becomes severely reduced. Kidney functional reserve is a specialist physiological concept describing the ability to increase filtration after a stimulus. Routine CKD staging does not measure it directly. eGFR is an estimate, not a percentage Glomerular filtration rate describes how much fluid the kidneys filter over time. Direct measurement is possible but is not needed for routine care. Estimated glomerular filtration rate, called eGFR, is usually calculated from blood creatinine, age and sex. UK equations no longer adjust results for ethnicity. Creatinine is a waste product influenced by muscle mass, diet, medicines and recent illness. These factors can make creatinine based eGFR less accurate for some people. An eGFR of 50 does not mean that exactly half of kidney function remains. The number is an estimated filtration rate standardised to body surface area. Small changes can reflect biological or laboratory variation. A new eGFR below 60 is repeated promptly to check for acute deterioration or a misleading result. Urine albumin adds different information Albuminuria means that more albumin than expected is passing into urine. It can indicate damage to the kidney's filtering barrier. The urine albumin:creatinine ratio, called ACR, compares urine albumin with urine creatinine. This adjustment reduces the effect of urine concentration. NICE classifies ACR as A1 below 3 mg/mmol, A2 from 3 to 30, and A3 above 30. An ACR from 3 to 70 mg/mmol is usually confirmed with an early morning sample. Temporary illness, exercise, infection and other factors can affect albuminuria. Albuminuria can be important even when eGFR is normal. Lower eGFR and higher ACR independently predict kidney, cardiovascular and mortality risks. Classification uses cause, eGFR and albuminuria CKD is classified using its likely cause, GFR category and ACR category. This approach provides more information than one numbered stage. GFR categories run from G1 to G5. G5 means kidney failure, but it does not automatically mean that dialysis must begin immediately. Kidney replacement therapy includes dialysis or kidney transplantation. Decisions depend on symptoms, complications, preferences and specialist assessment, not one eGFR value alone. The Kidney Failure Risk Equation estimates the five year chance of needing kidney replacement therapy. It combines age, sex, eGFR and ACR in adults with suitable CKD categories. Risk categories guide monitoring, referral and conversations. They do not predict one person's future with certainty. CKD has many possible causes Diabetes and hypertension are common causes or contributors, but the pathways are not simply identical vascular wear. Diabetes can affect glomerular pressure, filtration barriers, metabolism and inflammatory pathways. Hypertension can damage kidneys, while kidney disease can also raise blood pressure. Other causes include glomerular disease, inherited conditions, urinary obstruction, recurrent stones, autoimmune disease, medicines and repeated acute kidney injury. More than one cause can be present. A clinician should not attribute CKD to diabetes or hypertension without considering the complete pattern. Urine blood, heavy albuminuria, rapid change, health problems in the family or structural symptoms can suggest another cause needing targeted assessment. Acute kidney injury is different Acute kidney injury, called AKI, is a sudden decline in kidney function over hours or days. It can occur with dehydration, infection, obstruction, medicines or severe illness. A person can have AKI without CKD, CKD without AKI, or both together. CKD increases susceptibility to AKI, and AKI can increase later CKD risk. A new reduced eGFR should not be labelled chronic until acute causes and persistence have been considered. NICE advises repeating a newly reduced eGFR within two weeks. This helps identify acute deterioration while longer term results establish chronicity. Progression is variable and often non linear CKD is not progressive in many people. Kidney function can remain stable for years, fluctuate or decline at changing rates. A single eGFR difference does not establish progression. Clinicians examine repeated measurements, ACR changes, treatment changes and episodes of acute illness. Some people are more likely to progress because of the cause, higher albuminuria, lower eGFR, uncontrolled blood pressure or repeated AKI. Cardiovascular disease is also a major risk. CKD care therefore protects the heart and circulation as well as the kidneys. Monitoring looks for several different problems Monitoring frequency depends on GFR category, ACR, cause, previous change, medicines and other conditions. Blood pressure, potassium, bicarbonate and haemoglobin can reveal complications or treatment effects. These measurements do not all change at the same CKD stage. Medicine doses may need review because kidneys remove many medicines. Dose decisions sometimes use creatinine clearance rather than laboratory eGFR. Non steroidal anti inflammatory drugs, called NSAIDs, can worsen kidney function or trigger AKI in susceptible people. They should not be started regularly without suitable advice. During vomiting, diarrhoea or dehydration, ask a clinician or pharmacist whether medicines need temporary adjustment. Do not stop prescribed medicines automatically without an agreed plan. Treatment can lower risk Treatment aims to address the cause, reduce cardiovascular risk, slow progression and manage complications. Blood pressure treatment, diabetes care, smoking support and cholesterol management may all matter. Selected people benefit from ACE inhibitors, ARBs or SGLT2 inhibitors. The appropriate medicine depends on albuminuria, diabetes, blood pressure, eGFR, potassium and other safety factors. Lifestyle advice should be individualised. People should not adopt severe protein, salt, potassium or fluid restrictions without clinical or dietetic guidance. Many people with CKD never need dialysis or transplantation. Early recognition creates opportunities to reduce risk rather than predict inevitable failure. A routine diabetes review example A 64 year old adult with type 2 diabetes and hypertension feels well. Their current eGFR is 52, and a result six months earlier was 54. Their urine ACR is 8 mg/mmol and remains raised in an early morning sample. These results support persistent CKD classified as G3aA2. The classification describes filtration and albuminuria. It does not prove that diabetes or hypertension is the sole cause. The clinician reviews blood pressure, medicines, urine blood, previous results and possible acute illness. Imaging or specialist referral depends on additional findings and risk. Management may include kidney protective treatment, cardiovascular risk reduction and personalised monitoring. The person should not change medicines from these results alone. When to seek urgent help Seek urgent GP or NHS 111 advice for much less urine than usual or sudden worsening swelling. Seek urgent advice for persistent vomiting, diarrhoea or inability to keep fluids down. Urgent advice is also needed for new breathlessness, marked drowsiness or confusion, especially during infection or dehydration. Call 999 for severe breathing difficulty, sudden confusion, persistent chest pain or collapse. This lesson explains general CKD principles. It cannot diagnose CKD, identify its cause or interpret your blood and urine results.

CKD is defined by persistent kidney abnormality and classified by cause, eGFR and albuminuria. eGFR is not a percentage, CKD often remains stable and a sudden change may represent acute kidney injury.