I recently gave a presentation on chronic kidney disease to a group of NPs and PAs in our latest ThriveAP+ cohort. They asked a number of excellent questions on the topic which led to some discussion about screening for proteinuria. It seems there’s a need to clear up some confusion around microalbuminuria. So, today, let’s get back to primary care basics with some Q&A on the topic.
Why do we screen for microalbuminuria?
Abnormal excretion of small amounts of albumin in the urine (called ‘moderately increased albuminuria’) can be an early marker of kidney injury caused by chronic diseases like diabetes or hypertension. Albuminuria is also a marker for cardiovascular disease risk.
Who should be screened for microalbuminuria?
Annual screening is indicated for all individuals with diabetes. Annual screening for proteinuria may also be effective in high-risk patients (older individuals and/or those with kidney disease risks like hypertension or diabetes).
Who should not be screened for microalbuminuria?
Screening for proteinuria is not considered cost effective in the general population of healthy individuals under the age of 60.
How should you test for microalbuminuria?
The standard urine dipstick generally won’t cut it for microalbuminuria. Its not sensitive enough unless the urine is highly concentrated. A few dipsticks have been formulated to test specifically for small amounts of albumin in the urine, but these still don’t yield quantitative results – we’ve got better options.
There are two recommended ways to test for albumin in the urine:
- 24-hour urine collection
- Spot urine collection / urine albumin-to-creatinine ratio
24-hour urine collection was the initial gold-standard for detection of albumin in the urine. But, collecting urine in a jug over the course of an entire day is a pretty cumbersome process. So, there is an allowable shortcut – measuring the urine albumin-to-creatine ratio from your run-of-the-mill pee in a cup urine collection. This test gives quantifiable results that are comparative to 24-hour urine collection; it measures the estimated protein excretion in grams per day.
A few pointers about spot urine collection for microalbuminuria:
- First morning void specimens are best. But, if this is inconvenient you can use urine collected at other times of the day.
- If you a repeat test is preformed to confirm results, comparing results collected at the same time of day is best.
- Patients should refrain from vigorous exercise within 24 hours of the test as exercise can cause transient microalbuminuria.
What’s the reference range for microalbuminuria?
A tiny amount of protein in the urine is normal – less than 30mg/day.
Moderately increased microalbuminuria (also called microalbuminuria) is defined by albumin excretion between 30mg and 300mg/day.
Severely increased albuminuria (also called macroalbuminuria) is defined as albumin excretion over 300 mg/day.
To establish a diagnosis of microalbuminuria, you must repeat the test twice, showing elevated albumin excretion on two of three urine collections over a three to six month period.
What if there’s protein in my patient’s urine and it’s not someone who’s at risk for kidney disease?
A number of conditions from UTI to vigorous exercise can cause microalbuminuria. If you can identify another cause, recheck the patient’s urine once the condition (ex. UTI) has resolved. In a patient with proteinuria and no obvious cause, your next step is to evaluate the patient for transient proteinuria (temporary excretion of protein caused by things like exercise or stress) and orthostatic proteinuria (protein appears in the urine when in the standing position).