Why does a spot ratio estimate 24-hour excretion?

Creatinine is excreted into the urine at a fairly constant rate of about 10 mmol per day, so dividing protein or albumin by creatinine cancels out how dilute or concentrated the sample is. The resulting ratio tracks the daily excretion closely enough to replace most timed collections.

How do PCR and ACR differ?

PCR measures total protein and is useful for detecting and following heavier proteinuria such as glomerular disease. ACR measures albumin specifically and is more sensitive at low levels, which is why it is the preferred test for screening diabetic and chronic kidney disease patients.

What are the KDIGO albuminuria categories?

On ACR, A1 is below 3 mg/mmol and is normal to mildly increased, A2 is 3 to 30 mg/mmol and moderately increased, and A3 is above 30 mg/mmol and severely increased. These categories combine with the eGFR stage to grade chronic kidney disease risk.

How do I convert from the older mg/g units?

Some labs report in milligrams per gram of creatinine rather than milligrams per millimole. Divide a mg/g value by about 8.84 to convert it to mg/mmol, which is the unit this calculator and most international guidelines use.

When is the spot ratio unreliable?

Very high or very low muscle mass changes creatinine excretion away from the 10 mmol assumption, and rapidly changing kidney function, heavy exercise or a high-protein meal can distort a single sample. An early-morning specimen and, where it matters, a confirmatory timed collection improve accuracy.

Protein:Creatinine Ratio & Albumin:Creatinine Ratio Calculator

Quantifying how much protein a patient is leaking into the urine once meant an awkward and unreliable 24-hour collection. A spot urine ratio gives almost the same information from a single sample, and this calculator turns the two raw lab numbers into a ratio, a daily estimate and a guideline category.

How it works

Because urinary creatinine excretion is roughly constant, dividing the analyte by creatinine corrects for urine concentration:

PCR (mg/mmol) = urine_protein (mg/L)  / urine_creatinine (mmol/L)
ACR (mg/mmol) = urine_albumin (mg/L)  / urine_creatinine (mmol/L)

With about 10 mmol of creatinine excreted per day, the 24-hour estimates follow directly. A PCR of 100 mg/mmol corresponds to roughly 1 g of protein per day, and an ACR multiplied by 10 estimates the daily albumin loss in milligrams. The tool maps the ACR onto the KDIGO A1, A2 and A3 bands and the PCR onto common proteinuria severity bands.

Tips and notes

Use an early-morning sample where possible, as it best reflects the steady state and avoids the effect of upright posture on protein leak. Keep both values from the same specimen and in the units shown: protein and albumin in mg/L, creatinine in mmol/L. If your laboratory reports milligrams per gram, divide by about 8.84 to convert to mg/mmol first. Remember that the 10 mmol creatinine assumption breaks down at the extremes of muscle mass and during acute kidney injury, so a confirmatory timed collection is still worthwhile when a precise figure changes management.