Kidney Function Test (KFT): What Creatinine, Urea, and eGFR Actually Mean

You got a Kidney Function Test done — maybe as part of an annual checkup, or because your doctor suspected something. Now you're looking at values like creatinine, BUN, eGFR, and uric acid, and wondering which ones matter and what "slightly high" actually means.

Here's everything you need to know, in plain language.

What Does a KFT Actually Measure?

Your kidneys filter your blood constantly — producing roughly 180 litres of filtrate every day from your blood (your full blood volume cycled through the kidneys many times over). They remove waste products, balance electrolytes, regulate blood pressure, and control how much water stays in your body.

A Kidney Function Test (also called KFT or RFT — Renal Function Test) measures waste products that build up in your blood when your kidneys aren't filtering well. If the kidneys slow down, these waste levels rise.

The Parameters — One by One

Serum Creatinine

Normal range:

Men: 0.7–1.2 mg/dL
Women: 0.5–1.0 mg/dL

Creatinine is a waste product from normal muscle activity. Your muscles constantly produce it, and your kidneys constantly filter it out. Because production is fairly constant, blood creatinine levels are a reliable indicator of how well your kidneys are filtering.

A high creatinine means the kidneys are not clearing it efficiently. But context matters enormously:

Muscular people naturally have higher creatinine (more muscle = more creatinine production)
Dehydration can push creatinine up temporarily
One elevated reading is very different from consistently high readings over months

A creatinine of 1.4 in a well-built 30-year-old athlete means something very different from a 1.4 in a 65-year-old with diabetes.

eGFR — Estimated Glomerular Filtration Rate

Normal range: ≥ 90 mL/min/1.73m²

eGFR is calculated from your creatinine, age, and sex. It estimates how many millilitres of blood your kidneys filter per minute. It's considered more meaningful than creatinine alone because it accounts for your age and body size.

| eGFR Value | What It Suggests | |---|---| | ≥ 90 | Normal kidney function | | 60–89 | Mildly reduced (monitor) | | 45–59 | Mildly-moderately reduced | | 30–44 | Moderately-severely reduced | | 15–29 | Severely reduced | | < 15 | Kidney failure territory |

Important: eGFR naturally declines with age. An eGFR of 72 in a healthy 70-year-old is very different from a 72 in a 35-year-old. Your doctor interprets this in context.

Blood Urea Nitrogen (BUN) / Serum Urea

Normal BUN range: 7–20 mg/dL
Normal Serum Urea range: 15–45 mg/dL

Urea is another waste product — this one from protein metabolism. When you eat protein, your body breaks it down and produces urea as a byproduct, which the kidneys filter out.

High urea can mean:

Kidneys not filtering well (similar to high creatinine)
High-protein diet
Dehydration (concentrates the blood)
Recent high-protein meal before the test

A useful number to look at is the BUN-to-Creatinine ratio. A ratio between 10:1 and 20:1 is normal. A much higher ratio (above 20:1) with normal creatinine often points to dehydration or bleeding in the digestive tract rather than kidney disease.

Uric Acid

Normal range:

Men: 3.5–7.2 mg/dL
Women: 2.6–6.0 mg/dL

Uric acid is a waste product from the breakdown of purines — compounds found in red meat, organ meats, shellfish, beer, and some vegetables like spinach. Normally, the kidneys filter uric acid out of the blood.

When uric acid is too high (a condition called hyperuricaemia), it can crystallise in joints causing gout — a very painful condition, particularly in the big toe. High uric acid over years is also linked to kidney stones and may contribute to kidney disease.

High uric acid in India is extremely common, driven by diet and genetics.

Serum Electrolytes — Sodium, Potassium, Chloride

Normal sodium: 136–145 mEq/L
Normal potassium: 3.5–5.1 mEq/L
Normal chloride: 98–107 mEq/L

Your kidneys regulate the balance of electrolytes in your blood. Sodium and potassium in particular are critical for heart and nerve function. Significantly elevated potassium (above 5.5) is a medical concern that needs prompt attention. Mild variations are common and often related to diet or hydration.

Bicarbonate (CO₂)

Normal range: 22–29 mEq/L

Bicarbonate measures how well your kidneys are maintaining your blood's pH balance. Low bicarbonate can indicate metabolic acidosis, which can occur in kidney disease. This is usually only interpreted alongside other values.

A Quick Reference Table

| Parameter | Normal Range | What It Measures | |---|---|---| | Serum Creatinine (men) | 0.7–1.2 mg/dL | Kidney filtering efficiency | | Serum Creatinine (women) | 0.5–1.0 mg/dL | Kidney filtering efficiency | | eGFR | ≥ 90 mL/min/1.73m² | Overall kidney function | | BUN | 7–20 mg/dL | Protein waste clearance | | Serum Urea | 15–45 mg/dL | Protein waste clearance | | Uric Acid (men) | 3.5–7.2 mg/dL | Purine waste clearance | | Uric Acid (women) | 2.6–6.0 mg/dL | Purine waste clearance | | Sodium | 136–145 mEq/L | Fluid/nerve balance | | Potassium | 3.5–5.1 mEq/L | Heart/nerve balance |

Why Do Indians Get KFTs Done?

Kidney disease is one of the fastest-growing health concerns in India. The two biggest causes of chronic kidney disease (CKD) here are diabetes and hypertension — both extremely common. If you have either condition, a KFT at least once a year is important.

Other reasons a KFT gets ordered:

Swelling in the face, feet, or ankles (fluid retention)
Foamy or dark urine
Frequent or reduced urination
Back pain near the kidneys
Routine annual health checkup
Monitoring if you take NSAIDs (painkillers like ibuprofen/diclofenac), which can stress kidneys over time
Before starting certain medications

What Mildly High Creatinine Usually Means

The most common finding that worries people: creatinine of 1.3–1.5 when the upper limit is 1.2.

Before concluding anything serious, your doctor will consider:

Was this a one-time reading or consistently elevated over months?
Were you dehydrated when the test was taken?
Did you eat a very large protein meal the night before?
Are you on NSAIDs or any medication that can affect kidneys?
Do you have diabetes or hypertension?

A single mildly elevated creatinine with a normal eGFR is very different from a pattern of rising creatinine over years.

Questions to Ask Your Doctor

If your KFT has flagged values, ask:

Is my creatinine elevation new, or has it been trending upward over time?
What's my eGFR, and what does it mean for my age?
Do I need to reduce protein intake or change my diet?
Should I be drinking more water each day?
Are any of my regular medications (painkillers, supplements) affecting my kidneys?

The Takeaway

Your KFT is most useful as a trend over time, not as a one-time reading. One slightly elevated creatinine with no symptoms is rarely cause for panic — but it's absolutely worth following up. Kidneys are remarkably resilient organs, and when caught early, most kidney health issues are very manageable.

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Medical disclaimer: This article is for educational purposes only. It does not constitute medical advice, and no information here should be used to self-diagnose or self-treat. Always consult a qualified doctor for interpretation of your test results and any medical decisions.