Urine Protein to Creatinine Ratio (PCR) Calculator
Enter your urine protein and creatinine values from a spot urine sample to calculate the protein-to-creatinine ratio (PCR), a reliable estimate of daily proteinuria without the inconvenience of a 24-hour urine collection. You get the PCR value, the Ginsberg classification, and the KDIGO proteinuria category. Switch between mg/dL, mg/L, and mmol/L depending on how your lab reports the results.
Formula
Worked example
A spot urine sample shows protein 30 mg/dL and creatinine 150 mg/dL. PCR = 30 / 150 = 0.20 g/g. This sits at the upper limit of normal on the Ginsberg scale and represents an estimated protein excretion of about 200 mg/day, which is KDIGO A1-A2 borderline. Clinically, it should be repeated on a first-morning void.
What is the protein-to-creatinine ratio?
The urine protein-to-creatinine ratio (PCR, also called UPCR) is calculated by dividing the protein concentration by the creatinine concentration in a spot (random) urine sample. Because urine creatinine is excreted at a relatively constant rate throughout the day, it corrects for variable urine dilution - a very dilute sample with 100 mg/dL protein means something very different from a concentrated one. The ratio therefore gives a reliable estimate of how much protein is being lost per day without the inconvenience of collecting all urine for 24 hours. Ginsberg et al. (1983) demonstrated that the PCR in mg/mg (or g/g) closely approximates grams of protein excreted per day, a finding since confirmed in large studies of adults with glomerular disease, diabetes, and hypertension.
How to read your result
A PCR below 0.2 g/g is considered normal for adults. Healthy kidneys keep almost all protein in the bloodstream - the glomerular filtration barrier is too tight to let large proteins through, and any small proteins that do pass are largely reabsorbed in the tubules. A PCR of 0.2-3.5 g/g signals proteinuria that requires further investigation. This range covers a wide spectrum of conditions, from benign orthostatic (postural) proteinuria in young adults to progressive glomerular diseases such as IgA nephropathy, focal segmental glomerulosclerosis, and diabetic nephropathy. A PCR above 3.5 g/g is in the nephrotic range, associated with nephrotic syndrome (edema, hypoalbuminemia, hyperlipidemia, hypercoagulability). In pregnancy, a PCR of 0.3 g/g or above is the threshold for diagnosing significant proteinuria in the context of preeclampsia screening.
KDIGO 2012 proteinuria categories
The Kidney Disease: Improving Global Outcomes (KDIGO) guidelines introduced three proteinuria categories to stage chronic kidney disease alongside eGFR. Category A1 covers normal to mildly increased proteinuria (below 150 mg/day for total protein, or below 30 mg/day for albumin). Category A2 is moderately increased (150-500 mg/day). Category A3 is severely increased (above 500 mg/day). Higher categories predict faster CKD progression, greater cardiovascular risk, and greater benefit from renin-angiotensin system blockade. An eGFR alone, without proteinuria staging, misses a major dimension of risk - two patients with the same eGFR of 45 mL/min/1.73m2 but PCRs of 0.1 versus 2.0 g/g have very different prognoses.
Limitations and important caveats
The PCR is a good but imperfect surrogate for 24-hour protein excretion. It can be falsely low if the urine is highly concentrated (very high creatinine) or falsely high if urine is very dilute. Samples should ideally be taken from the second morning void (not first, which accumulates overnight), avoiding exercise, fever, or urinary tract infection, which can all transiently raise protein. The test is for total protein. When glomerular disease causes primarily albumin loss, an albumin-to-creatinine ratio (ACR) is often preferred, because early diabetic nephropathy and other conditions initially cause albumin leakage before total protein rises significantly. A PCR below 0.3 g/g that is predominantly non-albumin protein (as in tubular disease or multiple myeloma) is easy to miss with ACR alone. Always interpret PCR alongside clinical history, blood pressure, serum creatinine, eGFR, and urine microscopy.
PCR interpretation: Ginsberg criteria and KDIGO proteinuria categories
| PCR (g/g) | Estimated g/day | Ginsberg category | KDIGO category | Clinical action |
|---|---|---|---|---|
| <0.2 | <200 mg | Normal | A1 (<150 mg/day) | Reassure, retest if symptomatic |
| 0.2-0.5 | 200-500 mg | Elevated | A1-A2 boundary | Repeat on first-morning void |
| 0.5-1.0 | 500 mg-1 g | Elevated | A2-A3 boundary | eGFR, sediment, BP assessment |
| 1.0-3.5 | 1-3.5 g | Elevated | A3 (severe) | Nephrology referral, renal workup |
| >3.5 | >3.5 g | Nephrotic range | A3 (severe) | Urgent nephrology referral |
Ginsberg et al. (1983) validated spot PCR as a surrogate for 24-hour protein excretion. KDIGO 2012 categories are used in CKD staging. Values are in g/g or the equivalent mg/day.
Frequently asked questions
What is a normal protein-to-creatinine ratio?
For adults, a PCR below 0.2 g/g (corresponding to roughly 200 mg of protein per day) is considered normal. Many laboratories use a slightly lower cut-off of 0.15 g/g (150 mg/day) as the upper limit of normal, in line with the KDIGO A1 category. In pregnancy, the key threshold is 0.3 g/g (300 mg/day), above which significant proteinuria is present and preeclampsia screening is warranted.
Is a spot PCR as accurate as a 24-hour urine collection?
For most clinical purposes, yes. Ginsberg et al. showed strong correlation between spot PCR and 24-hour protein excretion. The spot test is more practical, avoids errors from incomplete 24-hour collections, and gives results within minutes. The 24-hour collection is still used in some research settings and for monitoring in specific conditions, but guidelines increasingly favour the spot PCR for both diagnosis and routine monitoring.
What causes protein in urine?
The most common causes of persistent proteinuria are diabetic nephropathy, hypertensive nephrosclerosis, IgA nephropathy, focal segmental glomerulosclerosis, and minimal change disease. Transient proteinuria (resolving on repeat testing) can result from fever, heavy exercise, orthostatic proteinuria (common in healthy young adults who are upright all day), or urinary tract infection. Overflow proteinuria from light chains in multiple myeloma or myoglobin in rhabdomyolysis causes elevated total protein with a low or normal albumin fraction.
What is nephrotic-range proteinuria?
Nephrotic-range proteinuria is conventionally defined as protein excretion above 3.5 g per day (or a PCR above 3.5 g/g). This level of protein loss causes the clinical syndrome of nephrotic syndrome: generalized edema from low serum albumin, high blood cholesterol and triglycerides, and an increased risk of clotting. Common causes include minimal change disease, membranous nephropathy, focal segmental glomerulosclerosis, and diabetic nephropathy. Renal biopsy is usually needed to identify the specific cause and guide treatment.
What is the difference between PCR and ACR?
Both ratios correct for urine dilution by dividing by creatinine. PCR (protein-creatinine ratio) measures total urine protein including albumin, globulins, and other proteins. ACR (albumin-creatinine ratio) measures only albumin. ACR is more sensitive for early glomerular damage - particularly early diabetic nephropathy and hypertensive nephrosclerosis - because these conditions initially cause selective albumin leakage before total protein rises. PCR detects a wider range of conditions including tubular proteinuria and overflow proteinuria from immunoglobulin light chains. Guidelines often recommend ACR for CKD screening in diabetes and hypertension, and PCR for broader proteinuria assessment.
How should I prepare for a urine protein test?
For the most accurate result, avoid vigorous exercise for 24 hours before the test (exercise can transiently raise protein levels), collect the second morning void rather than the first (which can be concentrated from overnight), and postpone if you have a urinary tract infection or fever. Avoid collecting during your menstrual period if possible. Your doctor may also ask you to temporarily hold medications such as ACE inhibitors or NSAIDs in specific protocols, but do not stop any medication without medical advice.