UACR testing:
intended use and more.

Intended use
In vitro diagnostic test for quantitative determination of albumin, creatinine and albumin/creatinine ratio (ACR) in human urine.

Summary and test explanation
Albumin is a small protein present in high concentrations in plasma. Normally only small amounts of albumin are excreted in urine. Sustained elevations of urinary albumin concentrations are known as microalbuminuria. Microalbuminuria is defined as an ACR between 30 -300 mg/g in at least two of three urine samples within a three-to-six-month period1,3.

Creatinine is a degradation product of the muscle tissue protein creatine. All creatinine crosses the glomerular basement membrane and is excreted in the urine. As muscle degradation is a continuous process, creatinine is filtered at a constant rate. Measurements of creatinine in urine will thus correct for varying diuresis and calculating the ACR will give a more accurate result of the albumin excretion rate2,3.

Microalbuminuria is connected to several late complications of diabetes such as retinopathy and neuropathy, as well as essential hypertension, preeclampsia, cardiovascular diseases, inflammatory conditions, and mortality. Today ACR is a predictive marker of great importance in the early detection of kidney disease and identification of patients at risk for complications of diabetes or hypertension4,5,6.

Recommendations from American Diabetes Association: At least once a year, assess urinary albumin (e.g., spot urinary albumin-to-creatinine ratio) and estimated glomerular filtration rate in patients with type 1 diabetes with duration of ≥ 5 years, in all patients with type 2 diabetes, and in all patients with comorbid hypertension2.)

Test inclusions
Urine Albumin, Urine Creatinine, Albumin: Creatinine ratio.

Expected turnaround time

  • One day
  • Turnaround time is defined as the amount of time it takes for the sample to arrive in the lab and results are reported

Specimen requirements

  • Volume: 10mL (min 2mL)
  • Container: Plastic urine container
  • Collection: Collect random urine without preservatives

Storage/stability

  • Human urine samples can be stored refrigerated for 5 days. Stored samples should be mixed well by inverting the cup 8–10 times before collecting the sample.
  • Do not use urine samples which have been previously frozen.
Refrigerated 5 days
Ambient Unacceptable
Frozen Unacceptable

Causes for rejection

  • Bloody specimen

Methodology

  • Albumin: Solid Phase Immunochemistry
  • Creatinine: Enzymatic

Reference interval

Albumin
(mg/L)		 Creatinine
(mg/dL)		 ACR
(mg/g)
Reportable range 5.0 – 200.0 16.4 – 339.9 1.0 – 1225.0
Interval 0.1 0.1 0.1
Expected values (may fluctuate based on gender or age)

The expected values are according to recommendations given by the American Diabetes Association1, 2.

Category Spot Collection ACR
mg/g
Normal 0 – 29
Moderately 30 – 300
Severely increased > 300

The concentration of creatinine in urine is normally within the range of 34–147 mg/dL7.

References:

  1. KDIGO, Kidney Int Suppl. 2013;3:1-150
  2. American Diabetes Association, Standards of Medical Care in Diabetes – 2019. Diabetes Care, January 2019;42(Supplement 1)
  3. Burtis C. A., Ashwood E. R., Tietz Fundamentals of Clinical Chemistry, 5th ed.
  4. Janssen, W. M. T. et al., Low Levels of Urinary Albumin Excretion are Associated with Cardiovascular Risk Factors in the General Population. Clin Chem Lab Med 2000; 38(11):1107-2000.
  5. Nisell H. et al., Acta Obstet Gynecol Scand 2006;85(11): 1327-30.
  6. Bloomgarden Z. T., Nephropathy and retinopathy. American Association Annual meeting, 1998.
  7. Foss OP. Fysiologi Patofysiologi Klinisk Kjemi. Noen momenter for fysiokjemikere, 2nd ed. Ullevål sykehus, Oslo, 1981; 99.