Several tests can be done to assess a lupus patient for kidney disease.
Measurement of Glomerular Filtration Rate and Proteinuria – The glomerular filtration rate is a measure of the efficiency of kidneys in filtering blood to excrete metabolic products. Typically this is done by collecting a 24-hour urine sample for measurement of creatinine clearance. Impairment of renal function by lupus nephritis results in reduced levels of creatinine clearance. The 24-hour urine sample can also quantify protein loss.
Protein/Creatinine Ratio – Performed on a one-time voided specimen, rather than from a 24hour collection, this test is useful as a measure of protein loss and is more convenient for patients.
Urinalysis – Urinalysis can indicate the presence or extent of renal disease. For example, proteinuria can be a reliable indicator of renal disease. The presence of RBCs, WBCs, and cellular casts, particularly red cell casts, in the urine also indicates renal disease.
Measurement of Serum Creatinine Concentration – Creatinine is a waste product of muscle metabolism that is excreted by the kidneys. Loss of renal function as a consequence of lupus nephritis causes increases in serum levels of creatinine. The concentration of creatinine in the serum can be used to assess the degree of renal impairment.
Kidney Biopsy –Kidney biopsy can be used to determine the presence of immune complexes and the presence, extent, and type of inflammation in the glomeruli. Diagnosing the extent and type of inflammation may help to determine a treatment program for lupus.