CKD lab panel: eGFR, creatinine, albuminuria, and what your kidney team is actually watching
Anchor biomarkers: eGFR, creatinine, urine albumin-to-creatinine ratio (uACR), cystatin C
TL;DR
- •CKD is staged on TWO axes, not one: eGFR (how well the kidneys filter) AND albuminuria (uACR — how much protein leaks into urine). A 'normal' eGFR with an elevated uACR is still kidney disease, and the albuminuria axis is the one most often missed.
- •A single eGFR value is not a diagnosis. CKD means abnormalities persisting for more than 3 months — the trajectory across repeated panels matters more than any one number.
- •Creatinine-based eGFR can mislead in people with very high or very low muscle mass. Cystatin C offers a muscle-independent check, and the combined creatinine + cystatin C equation is the most accurate routine estimate.
What each marker tells you
| Marker | Reference range | What it means |
|---|---|---|
| eGFR (estimated glomerular filtration rate) | ≥ 90 (G1) · 60–89 (G2) · 45–59 (G3a) · 30–44 (G3b) · 15–29 (G4) · < 15 (G5) mL/min/1.73m² | The core filtration estimate, calculated from creatinine (and ideally cystatin C) using the race-free 2021 CKD-EPI equations. Staging requires persistence over 3+ months. |
| Creatinine (serum) | ~0.6 – 1.3 mg/dL (varies by lab, sex, muscle mass) | Muscle-derived waste product the kidneys clear. The input to creatinine-based eGFR — which is why muscle mass, diet, and certain drugs can skew the estimate. |
| Cystatin C | ~0.6 – 1.0 mg/L (varies by lab) | Filtration marker produced by all nucleated cells — largely independent of muscle mass. Used to confirm CKD when creatinine-based eGFR is borderline or body composition is atypical. |
| uACR (urine albumin-to-creatinine ratio) | < 30 mg/g (A1) · 30–300 mg/g (A2) · > 300 mg/g (A3) | The second staging axis. Albumin leaking into urine signals glomerular damage and independently predicts both kidney progression and cardiovascular risk — even when eGFR is normal. |
| BUN (blood urea nitrogen) | ~7 – 20 mg/dL | A second waste-product marker. Affected by hydration, protein intake, and steroids — interpreted alongside creatinine, not alone. |
| Potassium | 3.5 – 5.0 mEq/L | Failing kidneys can lose the ability to excrete potassium. Also monitored because key CKD medications (ACE inhibitors, ARBs, MRAs) can raise it. |
| Bicarbonate (CO2) | 22 – 29 mEq/L | Low values indicate metabolic acidosis, which accelerates CKD progression and muscle loss — treatable when caught. |
| Phosphorus | 2.5 – 4.5 mg/dL | Rises as filtration falls (usually stage 4+). Drives the bone-mineral complications of advanced CKD. |
| PTH (parathyroid hormone) | ~15 – 65 pg/mL (varies by lab and CKD stage) | Rises early in CKD as the body compensates for phosphate retention and low active vitamin D — a window into bone-mineral health. |
| Hemoglobin | 13.5 – 17.5 g/dL (men) · 12.0 – 15.5 g/dL (women) | The kidneys make erythropoietin. Anemia appearing alongside falling eGFR is a common, treatable CKD complication. |
Reference ranges vary by laboratory and CKD stage. The eGFR (G1–G5) and albuminuria (A1–A3) categories follow the KDIGO 2024 staging system — your risk is read off the combination of the two, not either alone.
Three real patterns Phi Longevity has seen
Example patterns · synthetic data drawn from Phi Longevity's scenario library. Not real patient records.
Pattern 1 — The "normal creatinine, disappearing kidney" pattern.
A 74-year-old with creatinine 1.1 mg/dL — 'normal' on the lab report. But she weighs 52 kg with low muscle mass, and her calculated eGFR is 48 (stage G3a). Her uACR is 85 mg/g (A2). Because creatinine looked normal, no one flagged it for two years while the eGFR drifted from 61 to 48. This is the most common way early CKD hides in plain sight: creatinine stays in range while filtration quietly declines. The right read: stage G3a/A2 CKD — confirm with cystatin C, check the trajectory across every prior panel, and start kidney-protective therapy discussion now, not at stage 4.
Example pattern · synthetic data
Pattern 2 — The "missed albuminuria" pattern.
A 58-year-old with type 2 diabetes. eGFR 88 — comfortably 'normal.' But uACR is 240 mg/g (A2, nearly A3). By eGFR alone he has no kidney disease; on the KDIGO two-axis grid he is already at high risk of progression and elevated cardiovascular risk. Large consortium data show albuminuria predicts mortality and kidney failure independently of eGFR. This pattern is exactly why guidelines call for annual uACR screening in diabetes — and why a panel that never included a urine albumin test can produce false reassurance.
Example pattern · synthetic data
Pattern 3 — The "stable stage 3, well-defended" pattern.
eGFR 44 (G3b) — but the trend over three years reads 47 → 45 → 44, uACR fell from 210 to 60 mg/g on an ACE inhibitor plus an SGLT2 inhibitor, potassium 4.6, bicarbonate 24, hemoglobin 13.1, PTH mildly elevated and stable. Blood pressure at target. This is what successfully defended CKD looks like: the stage number sounds alarming, but the trajectory is nearly flat and the albuminuria is falling. Most patients with stage 3 CKD on modern therapy never reach dialysis — the trend across panels is what tells you the defense is working.
Example pattern · synthetic data
Questions to bring to your doctor
- What is my eGFR trend over the last 2–3 years — not just today's value?
- When was my last urine albumin-to-creatinine ratio (uACR)? If never — can we add it today?
- What is my KDIGO risk category on the combined eGFR + albuminuria grid (e.g., G3a/A2)?
- Would a cystatin C–based eGFR change my staging, given my body composition?
- Am I a candidate for kidney-protective therapy — ACE inhibitor/ARB, SGLT2 inhibitor, or finerenone?
- Which of my other medications (NSAIDs, PPIs, contrast dye) should be adjusted or avoided to protect my kidneys?
- Do my potassium, bicarbonate, phosphorus, PTH, and hemoglobin show any treatable CKD complications?
- At what eGFR or uACR threshold would you refer me to (or escalate within) nephrology?
What Phi Longevity adds beyond a single number
CKD care is fragmented by design: the primary-care doctor orders the metabolic panel, the endocrinologist watches the diabetes labs, the cardiologist adjusts the blood-pressure medications, and the nephrologist sees you twice a year — each holding a different slice of the record. Phi Longevity consolidates every lab report you upload into one longitudinal view: your eGFR trajectory across years and labs, your uACR trend against therapy changes, and the complication markers (potassium, bicarbonate, PTH, hemoglobin) in one place. You get a single printable summary that travels with you to every appointment — so no clinician is reading your kidneys from a single snapshot again.
Frequently asked questions
My eGFR is 55 — do I have kidney disease?
One value below 60 is a flag, not a diagnosis. CKD requires the abnormality to persist for more than 3 months, so the first step is a repeat panel (ideally with cystatin C) plus a uACR. Hydration, recent illness, medications, and muscle mass can all move a single reading.
Why does my doctor keep asking for a urine test when my blood work is fine?
Because albuminuria (uACR) is the second axis of kidney disease. Protein leaking into urine marks glomerular damage and predicts progression and cardiovascular events independently of eGFR. A normal eGFR with high uACR is still CKD — and still treatable.
What actually slows CKD down?
Blood-pressure control (often with an ACE inhibitor or ARB), SGLT2 inhibitors, treating the underlying cause (most commonly diabetes and hypertension), avoiding kidney-toxic drugs like chronic NSAIDs, and treating complications such as acidosis. Modern combination therapy has changed the trajectory of the disease — most stage 3 patients on current therapy never reach kidney failure.
Is eGFR accurate if I'm very muscular or very slight?
Creatinine-based eGFR assumes roughly average muscle mass, so it underestimates kidney function in bodybuilders and overestimates it in frail or sarcopenic patients. Cystatin C doesn't depend on muscle, and the combined creatinine + cystatin C equation is the most accurate routine option.
What stage means I need dialysis?
Dialysis or transplant becomes relevant at stage 5 (eGFR below 15) with symptoms — and preparation conversations typically begin in stage 4. The overwhelming majority of people with CKD never get there; cardiovascular protection is actually the more pressing issue at stages 1–3.
Why do potassium and bicarbonate matter for my kidneys?
They're the treatable complications. High potassium limits which protective medications you can take and carries cardiac risk; low bicarbonate (acidosis) accelerates both kidney decline and muscle loss and can be corrected. Both are cheap tests that change management.
My creatinine went up after starting an ACE inhibitor or SGLT2 inhibitor — is the drug hurting my kidneys?
A modest, stable creatinine bump (and a small early eGFR dip with SGLT2 inhibitors) is expected and usually reflects a pressure change inside the kidney's filters, not damage — these drugs protect kidneys long-term. A large or progressive rise is different and needs review. Never stop a kidney-protective drug without discussing the trend with your clinician.
References
All citations verified against PubMed / publisher of record 2026-05-25.
- 1.Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. (2024). KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney International. 105(4S):S117-S314. — Current global standard for CKD definition, the two-axis G/A staging grid, and management.PubMed →DOI →
- 2.Inker LA, Eneanya ND, Coresh J, et al. (2021). New Creatinine- and Cystatin C–Based Equations to Estimate GFR without Race. New England Journal of Medicine. 385(19):1737-1749. — The 2021 race-free CKD-EPI equations — basis for current eGFR reporting and the combined creatinine + cystatin C estimate.PubMed →DOI →
- 3.Levey AS, Coresh J. (2012). Chronic kidney disease. The Lancet. 379(9811):165-180. — Definitive review of CKD epidemiology, staging, and progression.PubMed →DOI →
- 4.Chronic Kidney Disease Prognosis Consortium; Matsushita K, van der Velde M, Astor BC, et al. (2010). Association of estimated glomerular filtration rate and albuminuria with all-cause and cardiovascular mortality in general population cohorts: a collaborative meta-analysis. The Lancet. 375(9731):2073-2081. — 1.2M-participant meta-analysis establishing eGFR and albuminuria as independent mortality predictors — basis for the two-axis framing.PubMed →DOI →
Reference ranges vary by laboratory. eGFR staging thresholds follow KDIGO 2024. Every link above opens in a new tab.
By Steve Pinedo
Co-founder, Phi Longevity
Last updated: 2026-07-22
Steve Pinedo is the Co-founder of Phi Longevity, the AI application that turns a confusing stack of lab reports, wearable data, and clinical notes into a single, integrated picture of your health. He started Phi Longevity to make proactive health and wellness far easier to achieve. He realized how difficult it was for clients to manage their own care, records and coordination so he assembled a comprehensive M.D. led clinical team behind the platform, packaging the proactive-care experience that delivered measurable outcomes (lower triglycerides, reduced body fat, improved LDL, balanced hormones, relief from long-running autoimmune conditions) for any patient with a complicated lab to use now with an application. More about Phi Longevity →