EXPERTQ&A

Proteinuria and : What’s the Difference? Cynthia A. Smith, DNP, CNN-NP, FNP-BC, APRN, FNKF

What exactly is the difference between TABLE Qthe -to- ratio and the Persistent Albuminuria Categories microalbumin in the lab report? How do they compare? Category Description UACR For the non- provider, the options for A1 Normal to mildly < 30 mg/g evaluating urine protein or albumin can seem con- increased (< 3 mg/mmol) fusing. The first thing to understand is the impor- tance of assessing for , an established A2 Moderately 30-300 mg/g marker for chronic disease (CKD). Higher increased (3-30 mg/mmol) protein levels are associated with more rapid pro- A3 Severely > 300 mg/g gression of CKD to end-stage renal disease and in- increased (> 30 mg/mmol) creased risk for cardiovascular events and mortality in both the nondiabetic and diabetic populations. Abbreviation: UACR, -to-creatinine ratio. Monitoring proteinuria levels can also aid in evaluat- Source: KDIGO. Kidney Int. 2012.1 ing response to treatment.1 Proteinuria and albuminuria are not the same low-up testing. While the UACR is typically reported thing. Proteinuria indicates an elevated presence as mg/g, it can also be reported in mg/mmol.1 Other of protein in the urine (normal excretion should be options include the spot urine protein-to-creatinine < 150 mg/d), while albuminuria is defined as an “ab- ratio (UPCR) and a manual reading of a reagent strip normal loss of albumin in the urine.”1 Albumin is a (urine dipstick test) for total protein. Only if the first type of plasma protein normally found in the urine 2 choices are unavailable should a provider consider in very small quantities. Albuminuria is a very com- using a dipstick. mon (though not universal) finding in CKD patients; Reagent strip urinalysis may assess for protein or is the earliest indicator of glomerular diseases, such as more specifically for albumin; tests for the latter are diabetic ; and is typically present becoming more common. These tests are often used even before a decrease in the glomerular filtration rate in a clinic setting, with results typically reported in the (GFR) or a rise in the creatinine.1 protein testing section. It is important to know which Albuminuria, without or with a reduction in esti- reagent strip urinalysis you are using (protein vs al- mated GFR (eGFR), lasting > 3 months is considered bumin) and how this is being reported. Additionally, a marker of kidney damage. There are 3 categories of test results depend on the urine concentration: Con- persistent albuminuria (see Table).1 Staging of CKD centrated samples are more likely to indicate higher depends on both the eGFR and the albuminuria cat- levels than may actually be present, while dilute sam- egory; the results affect treatment considerations. ples may test negative (or positive for a trace amount) While there are several ways to assess for protein- when in reality higher levels are present. uria, their accuracy varies. The 2012 : If a reagent strip urinalysis tests positive for protein, Improving Global Outcomes (KDIGO) guideline on confirmatory testing is recommended using the UACR the evaluation and management of CKD recom- or the UPCR (if the former is not an option). A 24-hour mends the spot urine albumin-to-creatinine ratio urine screen for total protein excretion or an albumin (UACR) as the preferred test for both initial and fol- excretion rate can be obtained if there are concerns about the accuracy of the previously discussed tests. Cynthia A. Smith practices at Renal Consultants, PLLC, in A urine albumin excretion rate ≥ 30 mg/24 h corre- South Charleston, West Virginia. sponds to a UACR of ≥ 30 mg/g (≥ 3 mg/mmol).1 Al-

OCTOBER 2019 mdedge.com/clinicianreviews Clinician Reviews 8e EXPERTQ&A

though 24-hour urine has been considered the gold is recommended. This can include assessment with standard, it is used less frequently today due to poten- urine protein electrophoresis.1­ —CS CR tial for improper sample collection, which can nega- tively affect accuracy, and inconvenience to patients.2 REFERENCES 1. Kidney Disease Improving Global Outcomes (KDIGO) CKD Work Group. As a final note, if there is suspicion for nonalbumin KDIGO 2012 clinical practice guidelines for the evaluation and manage- proteinuria (eg, when increased plasma levels of low- ment of . Kidney Int. 2013;3(suppl):1-150. 2. Ying T, Clayton P, Naresh C, Chadban S. Predictive value of spot versus molecular-weight or immunoglobulin light 24-hour measures of proteinuria for death, end-stage kidney disease chains are present), testing for specific urine proteins or chronic kidney disease progression. BMC Nephrology. 2018;19:55.

The National Kidney Foundation Renal Consult is edited by Jane S. Davis, CRNP, DNP, Council of Advanced Practitioners' a member of the Clinician Reviews editorial board, who (NKF-CAP) mission is to serve as is a nurse practitioner in the Division of Nephrology at an advisory resource for the NKF, the University of Alabama at Birmingham and is the nurse practitioners, physician communications chairperson for the National Kidney assistants, clinical nurse specialists, Foundation’s Council of Advanced Practitioners (NKF- and the community in advancing CAP); and Kim Zuber, PA-C, MSPS, DFAAPA, a semi- the care, treatment, and education retired PA who works with the American Academy of of patients with kidney disease and their families. Nephrology PAs and is a past chair of the NKF-CAP. CAP is an advocate for professional development, Clinician Reviews is the proud recipient of NKF-CAP’s research, and health policies that impact the delivery Nostradamus Award, recognizing the journal’s of patient care and professional practice. For more forethought and vision in supporting the contributions information on NKF-CAP, visit www.kidney.org/CAP. of Advanced Practitioners in nephrology.

OCTOBER 2019 mdedge.com/clinicianreviews Clinician Reviews 9e