Kidney health: early warning signs and what your blood tests can show

Diabetes and insulin resistance

Diabetes is the leading cause of chronic kidney disease in the UK and globally. Persistently elevated blood glucose damages the tiny blood vessels (glomeruli) inside the kidneys that filter waste from the blood, a condition called diabetic nephropathy. This damage accumulates silently over years, and by the time albuminuria (protein in the urine) becomes detectable, the structural damage to the glomeruli is already significant. People with type 2 diabetes or prediabetes benefit from annual kidney function monitoring, including both eGFR from a blood test and an albumin-to-creatinine ratio (ACR) from a urine test, because together they detect early damage that blood testing alone may miss.

High blood pressure

Hypertension is both a cause and a consequence of kidney disease. Chronically elevated blood pressure creates mechanical stress on the glomerular blood vessels, gradually impairing their filtering capacity. Conversely, as kidney function declines, the kidneys lose their ability to regulate sodium and fluid balance, which raises blood pressure further. This bidirectional relationship means that blood pressure control is one of the most important modifiable factors for both preventing and slowing the progression of kidney disease. Regular kidney function monitoring in people with hypertension gives early warning of whether blood pressure is causing structural kidney stress over time.

Genetic conditions and family history

Polycystic kidney disease (PKD) is the most common hereditary kidney disorder, affecting approximately 1 in 1,000 people in the UK. Cysts develop in both kidneys and enlarge progressively over decades, eventually impairing kidney function. PKD is typically identified through imaging rather than blood tests, but eGFR monitoring tracks functional decline over time. Alport syndrome, IgA nephropathy, and several other inherited conditions also affect the kidneys and may present with haematuria (blood in the urine) and gradual eGFR decline. Family history of kidney disease significantly increases personal risk and provides a strong rationale for regular monitoring.

NSAID use and medication effects

Non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen reduce blood flow to the kidneys by inhibiting prostaglandins that maintain glomerular perfusion. Regular or high-dose NSAID use is a common and underappreciated cause of kidney function decline, particularly in older adults, people with existing kidney disease, and those who are dehydrated. Contrast dyes used in CT and MRI scans, certain antibiotics, and some cancer treatments are also directly nephrotoxic. People who use NSAIDs regularly, or who have had recent contrast imaging or nephrotoxic drug treatment, benefit from kidney function monitoring.

Cardiovascular risk and the kidney-heart connection

Kidney disease and cardiovascular disease share many common risk factors and are bidirectionally linked. Reduced kidney function causes fluid retention, electrolyte imbalances and activation of hormonal systems that raise blood pressure and promote atherosclerosis. At the same time, cardiovascular disease reduces renal perfusion and accelerates kidney damage. This means that high cholesterol, elevated homocysteine, elevated CRP and other cardiovascular biomarkers are directly relevant to kidney health, and comprehensive monitoring of both kidney function and metabolic markers provides the most complete risk picture.

Age-related decline in kidney function

Kidney function declines gradually with age, even in the absence of any specific kidney disease. The average eGFR falls by approximately 0.5-1 ml/min/1.73m2 per year from around the age of 40 onwards. This normal age-related decline means that older adults may have eGFR values below the standard reference threshold of 60 while not having clinically significant kidney disease. The distinction between normal ageing and pathological decline is made by looking at trends over time and at other markers of kidney damage, rather than any single eGFR reading. Regular monitoring across multiple years provides this trend information.

Dehydration and acute kidney injury

Acute kidney injury (AKI) describes a sudden and rapid decline in kidney function, most commonly triggered by severe dehydration, infection (particularly sepsis), blood pressure drops during surgery, or nephrotoxic substances. AKI is detectable through rising creatinine and falling eGFR on blood tests. In most cases, kidney function recovers fully with appropriate treatment, but recurrent AKI episodes accelerate the development of CKD over time. People who experience frequent episodes of illness-related dehydration, or who have had hospital admissions involving AKI, benefit from kidney function monitoring as part of routine health assessment.

The two key markers in kidney function testing are creatinine and eGFR, measured from a standard blood draw.

Creatinine is a waste product produced at a constant rate from the breakdown of muscle tissue. Healthy kidneys continuously filter creatinine out of the bloodstream. When kidney filtration capacity falls, creatinine accumulates in the blood. Rising creatinine levels are one of the earliest and most reliable indicators of declining kidney function, though the absolute level varies with muscle mass, diet and body size, which is why it is used within the eGFR calculation rather than as a standalone marker.

eGFR (estimated glomerular filtration rate) is calculated from creatinine, alongside age, sex and body size, using the CKD-EPI formula approved for use in the UK. eGFR estimates how many millilitres of blood the kidneys are filtering per minute. A normal eGFR is 90 or above. Values of 60-89 are generally considered within normal range in the absence of other signs of kidney damage. An eGFR persistently below 60 for three months or more indicates chronic kidney disease and requires further assessment. An eGFR is most informative when tracked over time: a steady value is reassuring; a declining trajectory is a meaningful signal even if the current value is within range.

Urea is another waste product that rises when kidney filtration is impaired, though it is less specific than creatinine because it is also raised by dehydration and high protein intake. Normal range without CKD is 2.5-7.8 mmol/L. Urea alongside creatinine and eGFR gives a more complete picture of kidney waste clearance.

Electrolytes: sodium, potassium, bicarbonate are tightly regulated by the kidneys. Disruption to potassium and sodium balance is a key complication of progressive CKD and can have serious cardiovascular consequences. Monitoring these alongside eGFR is important in people with known kidney disease.

Cholesterol, HbA1c and blood pressure are not kidney markers themselves, but they are the primary modifiable risk factors for CKD progression. A comprehensive blood panel that includes these alongside kidney markers provides the full picture of what is driving decline and where intervention can have the most impact.

For people with an eGFR below 60, or eGFR above 60 with signs of kidney damage (protein in urine), GP referral for further investigation is appropriate. This typically includes urine ACR to detect albuminuria, kidney ultrasound to assess structure and rule out obstruction, and blood pressure review. Kidney function blood testing is the entry point, not the endpoint, of kidney health assessment.

Blood sugar and insulin sensitivity

For people with diabetes or prediabetes, maintaining blood glucose within target range is the single most important intervention for preventing diabetic nephropathy. Each percentage point reduction in HbA1c is associated with a meaningful reduction in the risk of kidney complications. Dietary approaches that reduce refined carbohydrate intake, combined with regular exercise to improve insulin sensitivity, produce measurable reductions in HbA1c over 3-6 months that translate directly into lower kidney disease risk over time.

Blood pressure management

Target blood pressure for people with kidney disease is generally below 130/80 mmHg, which is lower than the standard population target. Reducing sodium intake, maintaining a healthy body weight, increasing potassium-rich vegetables and fruits (in people without advanced CKD where potassium restriction may be needed), and regular aerobic exercise all contribute to blood pressure reduction through mechanisms that are complementary to medication. Monitoring both kidney function and blood pressure together provides a more complete picture of how well these risk factors are being managed.

Hydration and kidney protection

Adequate hydration supports kidney filtration and reduces the concentration of waste products in the collecting system. The evidence for specific water targets is less clear than popular health messaging suggests, but consistent pale yellow urine throughout the day is a reliable indicator of adequate hydration. Avoiding prolonged dehydration, particularly during illness, exercise in heat or fasting, is a practical protective measure. For people with kidney stones, higher fluid intake is directly therapeutic, as it reduces stone-forming mineral concentration in the urine.

Protein intake and CKD

High protein intake increases the metabolic load on the kidneys, because processing protein generates nitrogen-containing waste products including urea and creatinine. For people with already reduced kidney function (eGFR below 60), moderate protein intake (0.6-0.8g per kg body weight per day) is typically recommended to slow progression. For people with normal kidney function and metabolic goals that include higher protein intake, monitoring eGFR periodically provides reassurance that the kidneys are handling the load without adverse effects.

Medication management

NSAIDs (ibuprofen, naproxen, diclofenac) should be used sparingly or avoided entirely in people with any degree of kidney function reduction. If you take regular NSAIDs for pain management, monitoring kidney function periodically and discussing alternatives with your GP is a prudent approach. Certain supplements, including high-dose vitamin C and some herbal preparations, can also affect kidney function and warrant consideration in the context of overall kidney health monitoring.