Creatinine and eGFR (Kidney Function)#

Not necessarily. A single eGFR below 60 means kidney function is mildly to moderately reduced at that moment. To diagnose chronic kidney disease (CKD), the abnormality has to persist for at least 3 months along with either:

• eGFR persistently below 60, OR
• Urine ACR persistently above 3 mg/mmol (kidney damage marker), OR
• Other persistent markers of kidney damage on imaging or urine testing

Canadian guidelines recommend repeating eGFR (and adding a urine ACR if not already done) 3 months after an initial abnormal result. If you have suddenly dropped from a previously normal eGFR, your clinician will usually repeat sooner.

No. Low creatinine almost never means kidney problems. Creatinine is a byproduct of muscle metabolism, so low creatinine usually just reflects:

• Less muscle mass (smaller body size, older age, vegetarian or vegan diet)
• Pregnancy (extra fluid in circulation dilutes creatinine)
• Liver disease (the liver also contributes to producing creatinine precursors)

If your eGFR is normal, low creatinine is not a clinical concern. The kidney-function summary is the eGFR.

Repeat the eGFR and add a urine ACR in about 3 months. In the meantime:

• Stay well-hydrated.
• Avoid regular use of non-prescription anti-inflammatories (ibuprofen, naproxen) unless your clinician has discussed it.
• If you have high blood pressure or diabetes, make sure those are well controlled.

A single mildly low eGFR (50 to 59) without other abnormalities is often a one-off and returns to normal on repeat - especially if you had a heavy-protein meal, dehydration, or strenuous exercise the day before.

Several common, temporary factors:

• Heavy meat meal in the past 24 hours
• Strenuous exercise in the past 24 hours
• Dehydration
• Some non-prescription supplements containing creatine
• Some prescription medications that interfere with how kidneys handle creatinine (without actually damaging the kidney) - certain blood-pressure medications and a few antibiotics

These should improve with a repeat test under better conditions.

• Lower muscle mass (smaller frame, older age, prolonged bed rest)
• Vegetarian or vegan diet
• Pregnancy
• Liver disease

In someone with very low muscle mass, the eGFR can overestimate true kidney function. In that situation, your clinician may order cystatin C instead, which is not influenced by muscle mass.

Cystatin C is a protein produced at a constant rate by nearly all cells in the body. Unlike creatinine, it does not depend on muscle mass or diet, so it can give a more accurate eGFR in people with:

• Very low muscle mass (frail older adults, amputees, after long illnesses)
• Very high muscle mass (body-builders)
• Vegan or vegetarian diet
• Discrepancy between creatinine-based eGFR and clinical picture

Most Canadian provinces do not fund cystatin C as a screening test. It is usually self-pay through TeleTest's partner labs.

ACR (albumin-to-creatinine ratio) measures how much of a blood protein called albumin is leaking into your urine. Healthy kidneys hold albumin back. Damaged kidneys - especially in diabetes and high blood pressure - leak small amounts of albumin into urine before eGFR drops.

A high urine ACR is one of the earliest signs of kidney damage and is a marker for higher cardiovascular risk too. It is often abnormal years before eGFR changes, which is why both tests are done together.

A sudden drop in eGFR from previously normal values is more concerning than a long-standing mildly low value. Possible causes:

• Dehydration
• A new medication (especially non-prescription anti-inflammatories, certain blood-pressure medications, or certain antibiotics)
• New illness (infection, vomiting, diarrhea)
• Recent surgery or contrast-dye imaging
• Heart failure or liver disease worsening

If your eGFR has dropped substantially from your baseline, please contact a clinician promptly - usually a same-day visit at urgent care or a walk-in clinic, or a TeleTest consultation if appropriate.

Common monitoring intervals:

• Daily non-prescription anti-inflammatories (ibuprofen, naproxen): if used regularly for more than a few weeks, check kidney function once and discuss with a clinician.
• Long-term lithium: every 3 to 6 months.
• Long-term certain blood-pressure medications (e.g., ACE inhibitors, ARBs): check 2 to 4 weeks after starting or changing dose, then annually.
• Long-term diuretics ("water pills"): annually.
• Certain biologic medications and some antibiotics have specific monitoring schedules - your prescribing clinician will advise.

• Control blood pressure - the single most important factor.
• Control blood sugar if you have diabetes or prediabetes.
• Stay well-hydrated - but no need to over-drink water.
• Avoid regular use of non-prescription anti-inflammatories unless discussed with a clinician.
• Stop smoking.
• Maintain a healthy weight.
• Limit excess protein if you already have reduced kidney function (your clinician will be specific).
• Limit alcohol.

It depends on the cause. Sudden ("acute") kidney injury from dehydration, illness, or a medication often improves once the cause is addressed. Long-standing ("chronic") reduction from diabetes or high blood pressure usually does not fully reverse, but the rate of decline can be slowed substantially with good blood-pressure and blood-sugar control.

Diabetes Canada recommends:

• Annual eGFR and urine ACR for everyone with diabetes
• More often if any abnormality is found
• More often if you have new high blood pressure or symptoms

This is one of the earliest signs of kidney damage, especially in diabetes and high blood pressure. It often precedes a drop in eGFR by years. Steps to take:

• Confirm with a repeat urine ACR (one abnormal result is not definitive).
• Tight control of blood pressure and blood sugar.
• Certain blood-pressure medications (ACE inhibitors and ARBs) specifically reduce urine protein and are often started in this situation.

A 24-hour urine collection directly measures creatinine clearance and is more precise. However, it is cumbersome (you collect every drop of urine for 24 hours) and the eGFR estimate from a blood test is accurate enough for most clinical purposes. A 24-hour urine is usually only done in specialty situations (very high or very low muscle mass, kidney transplant evaluation, certain hormone studies).

eGFR naturally declines about 1 mL/min/year after age 30, so many healthy older adults have eGFR in the 60 to 80 range. The KDIGO guideline considers eGFR 60 to 89 as mildly reduced (stage G2), which in an older adult with no other abnormalities is often considered normal aging and not a disease state. The combination matters: if your eGFR is 65, your urine ACR is normal, your blood pressure is well controlled, and you have no diabetes, your kidney health is generally fine - just monitored more regularly.