ObstetricsTier 2Topic

Urine protein: creatinine ratio

What it is

Spot urine protein:creatinine ratio (UPCR) - a quantitative estimate of proteinuria from a single random urine sample, avoiding the need for a 24-hour collection
Used primarily to confirm/quantify proteinuria in suspected pre-eclampsia
Well correlated with 24-hour urine protein (the historical gold standard) and has largely replaced it in routine practice due to speed and convenience

Principle

Creatinine excretion is relatively constant over time - normalising urine protein concentration to urine creatinine concentration corrects for variation in urine dilution, unlike a raw protein concentration (dipstick)

Thresholds and use

UPCR >=30 mg/mmol (approximately >=0.3 mg/mg) = significant proteinuria, consistent with >=300mg/24h
Should be sent whenever dipstick shows >=1+ protein in a hypertensive pregnant woman, or when pre-eclampsia is otherwise suspected
Values in an indeterminate mid-range are less reliable - if clinical suspicion remains high despite a borderline UPCR, a 24-hour collection can still be used

Acting on the result

Positive UPCR in a hypertensive woman after 20 weeks -> supports a diagnosis of pre-eclampsia (proteinuria is one of several possible end-organ features under current definitions, and remains the most commonly used)
Confirmed proteinuria -> escalate surveillance, consider admission, involve the obstetric team for delivery planning

Associations

Pre-eclampsia, gestational hypertension, chronic kidney disease unmasked/exacerbated by pregnancy

Key point

UPCR does not need to be repeated serially once pre-eclampsia is diagnosed - the degree of proteinuria does not predict severity and is not used to guide the timing of delivery once the diagnosis is made

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