Your Kidneys Filter 180 Litres a Day. A Walk Through Your KFT Report, Marker by Marker

eGFR: your kidneys' speed rating

If creatinine is the raw measurement, eGFR is the interpretation. It stands for estimated glomerular filtration rate, and it is expressed in millilitres per minute (usually per 1.73 square metres of body surface, a standardising detail you can safely ignore). Think of it as a speed rating for your kidney filters: how many millilitres of blood the filters are cleaning each minute.

The word "estimated" matters. Measuring GFR directly is a long, complicated procedure involving injected tracer substances, so laboratories calculate it from your creatinine level, age and sex using a formula. The current standard is the CKD-EPI 2021 equation, which dropped the old race coefficient after a National Kidney Foundation and American Society of Nephrology task force concluded race had no place in the calculation. Your report's eGFR number comes from this kind of maths, not from a direct measurement, which is one reason doctors confirm odd results with a repeat test rather than reacting to a single value.

What the bands mean, in broad terms (MedlinePlus and the National Kidney Foundation agree on the shape of this):

• 90 to 100 and above: filtration looks normal. (Some healthy young people run above 120; that is not a problem.)

• 60 to 90: mildly decreased. In older adults this can be normal ageing, and it only points toward kidney disease if other signs, like protein in the urine, are present.

• 15 to 60: decreased enough that your doctor will want to investigate and repeat the test.

• Below 15: the kidney-failure range, where specialist care becomes urgent.

Doctors also stage chronic kidney disease by eGFR, from G1 (90 and above) down through G3a (45 to 59) and G3b (30 to 44) to G5 (below 15). A diagnosis of chronic kidney disease needs the low number to persist for at least three months, because temporary dips happen. Below 60 for three months or more is the standard definition, and the National Kidney Foundation stresses that decisions are rarely made from one sample.

Two more honest notes about eGFR. First, it drifts down slowly with age even in healthy people. A 72-year-old with an eGFR of 68 is in a different situation from a 35-year-old with the same number.

Second, eGFR can look deceptively normal in very muscular people (their high creatinine gets read as poor filtration) and deceptively reassuring in frail elderly people (their low muscle mass keeps creatinine low even when filtration is poor).

Trends across your own past reports beat any single reading. Bring the old PDFs to the appointment.

Urea (BUN): the chattier of the two waste markers

Urea is the leftover from protein breakdown. Your liver makes it when it processes protein from food, releases it into the blood, and the kidneys filter it out. The test measures urea nitrogen in the blood, hence the name BUN: blood urea nitrogen. A typical adult reference band is around 7 to 20 mg/dL, though ranges vary by laboratory.

BUN is the chattier marker because so many everyday things move it. Reduced kidney filtration raises it, yes, but so does dehydration, a very protein-heavy diet, and even a stomach bleed (the digested blood becomes extra protein for the liver to process). On the other side, unusually low BUN can show up with very low protein intake or significant liver trouble, since the liver is the organ making the urea in the first place.

Doctors rarely read BUN alone. They read it next to creatinine, and the ratio between the two is where the detective work happens. A typical BUN-to-creatinine ratio sits between 10:1 and 20:1. When BUN is high but creatinine is sitting pretty, the usual suspect is dehydration or a protein load rather than failing kidneys: the urea went up for a non-kidney reason. When both climb together, the kidneys themselves move to the top of the suspect list. This is why the pair is ordered together in the first place. For the standalone details, there is the blood urea nitrogen (BUN) test page.

The electrolyte crew: sodium, potassium, and the acid-balance number

Most KFT panels carry electrolytes along because the kidneys are the body's salt managers. They decide, minute by minute, how much sodium and potassium to keep and how much to send out in urine. When filtration falters, this balancing act is one of the first things to wobble.

Sodium mostly reflects fluid balance. Abnormal values can point to hydration issues or hormonal causes, and your doctor reads them in context rather than in isolation.

Potassium is the one doctors watch with real attention. The usual reference band is about 3.5 to 5.0 (units vary by lab; check your report's column), and both directions matter, but high potassium in kidney disease is the serious one. Potassium affects how nerves and muscles work, including the heart muscle, and high levels can disturb the heart's rhythm with few warning symptoms. This is not meant to frighten you; it is meant to explain why your doctor takes a flagged potassium value seriously and may want a recheck quickly.

Bicarbonate (sometimes labelled CO2 or total CO2) is the acid-balance number. Healthy kidneys keep the blood's acidity in a tight range, and when they slow down, acid can accumulate, a state called metabolic acidosis. The NIDDK lists bicarbonate above 22 as the normal side of the line. A low value is one of the quiet complications of long-standing kidney disease, and it is treatable, which is another reason the panel includes it.

Calcium and phosphorus ride along in wider kidney panels because chronic kidney trouble disturbs bone-mineral balance. Typical bands quoted by the NIDDK are roughly 8.5 to 10.2 for calcium and 2.7 to 4.6 for phosphorus, always with the ranges-vary-by-laboratory caveat. High phosphorus with low calcium is a pattern doctors see in advancing kidney disease, and it connects to bone health and itchy skin in later stages. You do not need to memorise these; just know the panel is looking at more than waste. It is checking whether the kidneys are still managing the chemistry they are responsible for.

Uric acid: the gout marker that cuts both ways

Uric acid comes from the breakdown of purines, compounds found in the body's own cells and in certain foods. Most of it leaves through the kidneys. High levels can crystallise in joints, which is gout, the famously painful swollen-toe condition, and can also contribute to kidney stones.

MedlinePlus quotes typical adult bands of about 3.0 to 7.1 mg/dL for women and 4.0 to 8.6 mg/dL for men, with the usual ranges-vary-by-laboratory note (Mayo Clinic Laboratories quotes slightly tighter adult bands). The physically meaningful line is around 6.8 mg/dL, the point where uric acid starts being able to form crystals at body temperature, which is why gout treatment aims below 6.0 rather than merely "inside the reference range."

The kidney connection runs both ways, which is why uric acid sits in the KFT bundle. Kidneys that filter poorly excrete less uric acid, so the blood level rises. And sustained high uric acid is itself associated with kidney stress over time. Things that push it up include dehydration, alcohol, fructose-heavy drinks, and purine-rich meals. Interestingly, a normal uric acid result drawn during an acute gout flare does not rule gout out, because levels can dip during the attack itself. The serum uric acid test page has the standalone details.

Questions patients actually ask us

Do I need to fast before a kidney function test? Most doctors prefer a fasting sample: nothing but water for 8 to 12 hours before the draw. Creatinine itself does not strictly demand fasting, but when it is measured as part of a wider chemistry panel, fasting keeps every number comparable. Water is fine and actively helps, since hydrated veins are easier to draw from. If your doctor did not specify, book a morning slot and fast. It never hurts.

How long does the home collection visit take? Under ten minutes, start to finish. The phlebotomist finds a vein, draws one tube of blood, and tapes a cotton ball over the spot. Most people are surprised it is over that fast.

What does a high creatinine number mean? It means your kidneys are clearing this muscle-waste product more slowly than usual. But creatinine also shifts with dehydration, heavy exercise, muscle mass, and protein-heavy meals, so one reading is never a diagnosis on its own. Your doctor reads it alongside eGFR, your other numbers, and your history, and usually repeats it before drawing conclusions.

Can dehydration change my KFT results? Yes, and this is one of the most common reasons for a mildly alarming report. Being dehydrated can push up both creatinine and urea readings. Drink water normally the day before and have a glass or two on the morning of the test, unless your doctor gave you different instructions. If you were unwell with vomiting or diarrhoea before the test, mention it: your doctor may want a repeat once you are rehydrated.

Is the KFT different from a urine test? Yes, and they complement each other. The KFT measures waste products in your blood; a urine test shows what your kidneys are letting pass through, like protein or blood. Doctors often order both together, because each catches things the other can miss.

How often should I repeat the kidney function test? If you have diabetes, the American Diabetes Association recommends kidney screening, eGFR plus a urine albumin check, at least once a year. The same yearly rhythm applies to high blood pressure. Otherwise it depends on your reports and your doctor's advice; there is no fixed schedule for everyone.

When will I get my report? About 24 hours after the sample reaches the lab. The report arrives as a PDF with your values, the lab's reference ranges, and flags next to anything out of range.

My eGFR fell from 95 to 82 in a year. Should I worry? Probably not on that fact alone, but it is worth showing your doctor. eGFR naturally drifts with age, and small shifts between tests can come from hydration, recent illness, or different lab methods. What matters is the trend across several reports and whether urine tests show protein. A single dip is worth showing your doctor; the conversation matters more than the number.

Can I have coffee or tea on the morning of the test? Stick to water. Coffee and tea are mild diuretics and can nudge your hydration status, and milk and sugar break the fast. One plain glass of water, or two, is the ideal pre-test drink.

Does this test catch kidney disease early? Earlier than symptoms do, which is the point. But the blood KFT alone can miss the earliest damage: protein can start leaking into urine while eGFR still looks normal. That is why guidelines pair the blood test with a urine albumin check for screening. Together they catch trouble years before you would feel it.

Why blood alone doesn't close the case: the urine half

Here is something the blood numbers cannot tell you: whether protein is slipping through the filters. A healthy kidney keeps protein, especially albumin, in the blood. A damaged filter lets some through into the urine, and this leakage often starts before eGFR begins to fall. The National Kidney Foundation calls protein in the urine one of the earliest signs of kidney disease, and it means it.

The screening test is the urine albumin-to-creatinine ratio, usually written uACR or ACR. It is measured from a simple urine sample, no 24-hour jug collection needed for screening. Below 30 mg/g is the normal side. Between 30 and 300 suggests kidney damage. Above 300 indicates heavier leakage and higher risk, and it changes how doctors manage you. Like eGFR, a single abnormal result gets repeated before anyone acts on it.

A urine routine and microscopy test covers related ground from a different angle: it looks at the urine itself for protein, blood, sugar, crystals, and casts under the microscope. Many patients book the blood KFT and the urine test together in one morning visit, which is sensible: blood shows how filtration is doing, urine shows what the filters are letting through. Between them, very little hides.

This pairing is also what the guidelines ask for. The American Diabetes Association recommends that everyone with type 2 diabetes gets both a urine albumin check and an eGFR at diagnosis and then at least yearly, and that people with type 1 diabetes start five years after diagnosis. Once kidney disease is established, monitoring steps up to between one and four times a year depending on the stage. If your doctor wrote "KFT + urine routine" on the prescription, this is the logic behind it, and it is good medicine.

Who gets this panel written on their prescription

The KFT is one of the most commonly ordered panels in any lab, and the reasons cluster into a few familiar groups.

Diabetes and high blood pressure top the list, by a distance. These are the two biggest reasons kidneys wear out early, and the damage is silent for years. If you take medicines for either, expect this panel at least once a year. At our lab in Malad, we see the same faces return for it every twelve months, like a service appointment for a car that never complains.

Family history of kidney disease earns you earlier and more regular screening. Kidney trouble runs in families more than most people realise.

Certain long-term medicines get processed through the kidneys, and doctors order periodic KFTs to make sure the organs handling the drugs are holding up. Never stop a medicine because of a lab number; that decision belongs to your doctor, who weighs the number against why you are on the medicine.

Before contrast scans is a common one people do not expect. The dye used in some CT scans leaves the body through the kidneys, so radiology departments want a recent creatinine and eGFR before giving it, especially in people with known kidney issues, diabetes, or high blood pressure. A fresh KFT result can be the difference between a smooth scan day and a rescheduled one.

Age past 50, heart disease, and recurring urinary infections round out the usual list. None of these means something is wrong. They mean your doctor is doing the quiet, unglamorous work of checking the filters before they complain, which is precisely when checking is most useful.

The morning of the draw: fasting, water, and the knock on the door

The most common question at our door, once the draw is over, is whether fasting was really necessary. Here is the straight version. Most doctors prefer the KFT drawn after 8 to 12 hours of fasting, water allowed throughout. MedlinePlus puts it this way: when creatinine is measured as part of a broader chemistry panel, you may be asked to fast for up to 12 hours. Creatinine on its own does not strictly require it. The 8 to 12 hour fast is the safe, conservative approach that keeps every number on the report comparable to the last one, and since pathology reviewers consider it sound practice, it is what we recommend unless your doctor said otherwise.

The evening before and the morning of, keep it simple:

• Do: finish dinner by 9 or 10 pm for a 7 am draw, and keep a glass of water by the bed.

• Do: drink water freely on the morning of the test. Hydrated veins are easier to find, the draw goes faster, and mild dehydration will not muddy your numbers.

• Do: take your regular medicines as usual unless your doctor told you otherwise. Never skip a dose for a lab test on your own call.

• Do: book the earliest slot you can. Fasting hours pass easiest while you are asleep.

• Don't: eat anything after your fasting window starts, including a "small" biscuit with morning tea. Small does not count as fasting.

• Don't: have coffee, tea, or juice in the morning. Caffeine nudges hydration, and anything with calories breaks the fast.

• Don't: do a heavy workout the evening before. Intense exercise can temporarily push creatinine up.

• Don't: schedule it the morning after a big non-vegetarian feast if you can avoid it. A very protein-heavy dinner can nudge both creatinine and urea upward for a day.

When our phlebotomist knocks on your door in Malad or Kandivali at 7, the sequence is always the same: a strap around your upper arm, a couple of taps on the forearm to bring a vein up, a cold alcohol swab, and a prick that feels like a quick sharp pinch for about a second. Then the needle is out, a cotton ball goes on, tape over it, and you press it for a few minutes with your arm straight. One tube of blood is all the KFT needs. Home collection is free, early-morning slots are the easy ones, and full booking details sit in the last section below. If fasting rules for other tests confuse you, our fasting guide walks through the general logic.

Reading your report without spiralling

Your report will arrive in about 24 hours, usually a clean PDF with your values in one column, the reference range in the next, and small flags next to anything out of range. Read it once, then hand it to your doctor. In between, here is how to look at it without the 2 am worry spiral.

Start with the pair that matters most: creatinine and eGFR. If both sit inside their reference bands, the filtration story is reassuring. If creatinine is flagged high and eGFR low, look at the context before the conclusion. Were you fasting, hydrated, rested? Did a heavy workout or a protein-loaded dinner the day before play a part? A single flagged number is a question, not a verdict, and doctors watch trends across visits, not snapshots.

Next, scan the supporting cast. A high BUN with a normal creatinine leans toward dehydration or diet. Flagged potassium gets a quicker call to your doctor than flagged uric acid does, because potassium affects the heart's rhythm. Uric acid slightly over the line with no gout symptoms is usually a "watch and recheck" rather than an emergency.

Three habits will save you years of unnecessary worry. First, compare each number against the reference range printed on your own report, never against a friend's report from another lab or a number from the internet. Methods differ between laboratories, and ranges vary accordingly.

Second, keep your old reports. A creatinine that moved from 0.9 to 1.0 over three years tells a calmer story than one that moved from 0.9 to 1.3 in six months, and your doctor can only see that story if you bring the history.

Third, remember what the KFT does not do: it reads the kidneys, not everything. If your liver numbers look odd too, your doctor will likely order the liver panel alongside. The two often travel together, which is why our liver function test post makes a natural companion read.

So here is the whole protocol for a flagged number. Do the least dramatic useful thing: note which number it was, check whether you followed the fasting and hydration guidance, and take the report to your doctor at the next visit, sooner if potassium or eGFR are far out of range. That is the entire protocol. The test did its job by asking the question; the doctor's job is answering it.

Booking it in Mumbai, the easy way

The KFT is a home-visit test at heart. One call to 84250 40353, a morning slot, water by the bed, and the rest belongs to the phlebotomist. Our Malad lab never sleeps, so the sample is processed within hours and the PDF lands on your phone in about a day. Take it to your doctor for a short conversation, ideally over chai, not over worry. Unsure where to start? The full test list has the kidney panel right there.

For a deeper look than the standard panel, the Kidney – Advanced Renal Function Screening Panel widens the kidney markers into one screen. If you're doing an annual health sweep anyway, the Complete Kidney Health Panel wraps kidney markers into broader screening, and the full packages page shows where kidney markers sit inside the bigger checkups. The home page works as a starting point too.

References

• MedlinePlus: Creatinine Test; Estimated Glomerular Filtration Rate (eGFR) and GFR Tests; Uric Acid - Blood

• National Kidney Foundation: Know Your Kidney Numbers: Two Simple Tests; Estimated Glomerular Filtration Rate (eGFR)

• National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK): Your Kidney Test Results

• American Diabetes Association: Standards of Care in Diabetes: Chronic Kidney Disease and Risk Management (annual UACR and eGFR screening guidance)