Kidney function tests: creatinine, eGFR, urea and UACR

Kidney function tests are a group of blood and urine measurements, not one universal panel. Blood chemistry can show how well the kidneys are filtering and how fluid, electrolytes and acid–base balance look at that moment. A urine albumin-to-creatinine ratio (UACR) looks for albumin leakage, a different sign of kidney damage.

The two central measurements in chronic kidney disease (CKD) assessment are estimated glomerular filtration rate (eGFR) and urine albumin. They answer different questions and are most useful together and over time. One eGFR result—whether low, normal or unexpectedly changed—does not by itself diagnose or exclude CKD.

What may be included in a kidney panel?

The exact list varies by country, laboratory and clinical question. A blood kidney or renal profile commonly includes creatinine, calculated eGFR, urea or blood urea nitrogen (BUN), sodium and potassium. Some laboratories also include chloride and bicarbonate or total CO₂. A broader comprehensive metabolic panel overlaps with these measurements but also covers glucose, proteins, calcium and liver-related markers.

UACR requires a urine sample. It is not a hidden part of serum creatinine, a CMP or another blood chemistry panel. Check the itemised order and report if CKD assessment is the goal.

Creatinine and eGFR belong together

Creatinine is produced through normal muscle metabolism and cleared largely by the kidneys. A higher concentration can accompany reduced filtration, but the raw number is not a direct percentage of kidney function. Laboratories use creatinine together with factors such as age and sex in an equation to report eGFR, usually in mL/min/1.73 m².

The “e” matters: eGFR is an estimate, not a direct measurement. Creatinine generation differs between people. Very high or low muscle mass, amputation, frailty, a recent large cooked-meat meal and creatine supplements can make creatinine-based eGFR less representative of actual filtration. A clinician may use cystatin C or another method when greater accuracy would change a decision.

Creatinine-based eGFR also assumes that creatinine is reasonably stable. During acute illness, dehydration, rapidly changing kidney function or recovery from acute kidney injury, the value can lag behind what is happening in real time. A trend from comparable conditions is usually more informative than an isolated flag. Our creatinine and eGFR guide explains the marker in more depth.

A single eGFR does not diagnose CKD

KDIGO defines CKD by abnormalities of kidney structure or function that persist for at least three months and have implications for health. This may be a persistently reduced eGFR, persistent albuminuria or another established marker of kidney damage. A result collected during gastroenteritis, fever, surgery or another acute event may instead reflect a temporary change or acute kidney injury.

That is why clinicians first ask:

1. Is this result new, or is the same pattern present on earlier reports?
2. Was creatinine stable when eGFR was calculated?
3. Is UACR or another marker of kidney damage abnormal?
4. Could hydration, illness, medicines, diet, exercise or body composition explain part of the change?

An eGFR above 60 does not rule out kidney damage if UACR is persistently raised. Conversely, one eGFR below 60 is not enough to label a chronic disease without establishing chronicity and context.

Urea and BUN are related, but not identical labels

Protein breakdown produces urea, which is carried in blood and excreted by the kidneys. Many European and Ukrainian reports list urea, often in mmol/L. US reports commonly list BUN, which measures only the nitrogen portion of the urea molecule, usually in mg/dL. The numbers are therefore not directly interchangeable; use the units and reference interval on the actual report.

Urea or BUN is influenced by more than filtration. Dehydration, a high-protein intake, gastrointestinal bleeding and increased tissue breakdown can raise it, while low protein intake or impaired liver urea production can lower it. Clinicians read it alongside creatinine, eGFR and the clinical picture rather than using it alone to diagnose kidney disease.

Electrolytes and acid–base context

The kidneys help regulate sodium and potassium and recover bicarbonate, so these measurements add important context—especially when kidney function is substantially impaired or changing acutely. Chloride and bicarbonate or total CO₂ help assess acid–base patterns, but a blood chemistry panel does not identify every cause by itself.

Results may also reflect vomiting, diarrhoea, fluid loss, heart or endocrine conditions, and medicines such as diuretics, ACE inhibitors or ARBs. Haemolysis during collection can falsely raise potassium. A critical potassium result or a substantial unexpected change needs prompt professional review; do not adjust prescribed medicines or take electrolyte supplements based only on an online range.

UACR is a separate urine test

UACR compares albumin with creatinine in the same spot urine sample. The ratio partly corrects for how concentrated or dilute the urine is. A first-morning sample is preferred in some settings, although a random spot sample may be acceptable. Routine assessment does not usually require a 24-hour urine collection.

NIDDK considers UACR above 30 mg/g abnormal, but a raised result is not automatically permanent CKD. Exercise, fever, urinary infection, marked hyperglycaemia, menstruation and other temporary factors may influence urine albumin. A clinician may repeat the test to confirm persistence. The key distinction remains: eGFR estimates filtration from a blood measurement; UACR assesses albumin leakage in urine.

Why results can change temporarily

Interpret the whole set in the circumstances in which it was collected:

• Dehydration: vomiting, diarrhoea, fever, heavy sweating or low fluid intake can concentrate blood results and reduce kidney perfusion.
• Acute illness: infection, surgery and circulatory problems can make kidney function change quickly, reducing the reliability of a steady-state eGFR estimate.
• Muscle mass and activity: muscular people may have higher baseline creatinine; frailty or muscle loss may produce a deceptively low creatinine. Strenuous exercise can also cause a transient rise.
• Food and supplements: a large cooked-meat meal and creatine supplements may raise creatinine without the same change in measured filtration.
• Medicines: prescription and over-the-counter products can change filtration, potassium or hydration. NSAIDs are especially important to disclose during dehydration or acute illness.

Do not stop a prescribed medicine or force excessive water intake before testing. Follow the instructions from the ordering clinician and report medicines, supplements, recent illness and unusual exercise.

Repeat testing and trends

The appropriate repeat interval depends on the size and speed of the change, symptoms, previous results and risk factors such as diabetes or hypertension. A mildly unexpected result in a well person may be repeated after reversible factors are addressed. A rapidly rising creatinine, critical electrolyte result or acute symptoms can require same-day assessment rather than a routine repeat months later.

When comparing results, check units, laboratory method and collection conditions. Note whether creatinine was stable and whether UACR was collected during an infection or other temporary stress. For long-term CKD assessment, clinicians consider eGFR category and albuminuria category together, alongside cause and other risk factors.

When to seek urgent medical help

Seek urgent care for a major reduction or cessation of urine output, severe breathlessness, rapidly worsening swelling, confusion, fainting, seizures, persistent vomiting or marked weakness. Palpitations, chest symptoms or a laboratory warning about critically abnormal potassium also need urgent assessment.

Contact the ordering clinician promptly when creatinine changes sharply from baseline, eGFR falls during acute illness, there is visible blood in urine, or the laboratory asks for an urgent repeat. Urgency depends on the trajectory and symptoms, not merely whether a number is marked high or low.

Tracking kidney results with HealthLab

HealthLab can keep reports from different laboratories together and plot creatinine, eGFR, urea and electrolytes over time. Recording an acute illness, dehydration, a supplement or a laboratory change beside a result makes the trend easier to interpret with a clinician.

UACR should remain clearly labelled as a urine result rather than grouped as blood chemistry. HealthLab organises results and context; it does not establish a diagnosis or replace professional assessment.

Frequently asked questions

This material does not replace clinical advice. Kidney test interpretation always requires clinical context.