TABLE 2.

Overview of urinary renal biomarkers in cats with CKD

Biomarker	Origin	Type of molecule	Mechanism underlying increased levels	Validated assays in cats	Changes in cats with azotemic‐CKD	Non‐renal factors to consider
Biomarkers of glomerular damage
Albumin	Hepatocytes	IMW protein	Increased glomerular permeability	Feline‐specific ELISA 20 Human PETIA 33 Electrophoresis 86	Insignificant 33	Lower urinary tract disease; systemic disease 86 , 87 , 88 , 89
Transferrin	Liver (primarily) and other tissues	IMW protein iron‐transporting protein	Increased glomerular permeability	SDS‐PAGE 90	Increased 90
Biomarkers of tubular impairment
L‐FABP	Proximal tubular cells	LMW and fatty acid‐binding proteins	Increased tubular excretion	ELISA 91	Increased 91 , 92 , 93	Hyperthyroidism 91
NGAL	Epithelial cells of proximal tubules, neutrophils and other tissues	LMW protein and glycoprotein	Decreased tubular reabsorption and increased tubular excretion	ELISA 91 , 94	Increased 94 , 95 or insignificant 91	Pyuria; systemic disease 95
KIM‐1	Proximal tubular cells	Renal tubular transmembrane glycoprotein	Decreased reabsorption and increased excretion	ELISA 96	Not assessed
VEGF	Renal proximal tubules	Signaling protein	Decreased production	ELISA 97	Decreased 97	Hyperthyroidism 98
CysC	All nucleated cells	LMW protein and cysteine protease inhibitor	Decreased tubular reabsorption	Human PENIA 31 Human PETIA 32 , 36	Increased 32 or decreased 36	Hyperthyroidism 24
HSP72	Renal tubular cells	Stress‐induced cytoprotective protein	Increased tubular excretion	ELISA 99	Increased 99	Urethral obstruction 99
F2‐Isoprostanes	Kidney	Antioxidant	Increased production	ELISA 100	Decreased 100	Hyperthyroidism 101
CysB	Proximal tubular cells	LMW protein and cysteine protease inhibitor	Ruptured and death of tubular epithelial cells	ELISA 27	Not assessed
Clusterin	Renal tubular cells	LMW protein and glycoprotein	Increased production	ELISA 27	Not assessed
Biomarkers of renal fibrosis
TGF‐β1	Parenchymal and inflammatory cells	Cytokine and pro‐fibrotic mediator	Increased production	ELISA 102 , 103	Increased 102 or insignificat 103
PIIINP	Collagen	Amino‐terminal propeptide of type III collagen	Decreased reabsorption	ELISA 104	Increased 104

Abbreviations: CysB cystatin B, CysC, cystatin C; HSP‐72, heat shock protein‐72; IMW, intermediate molecular weight; KIM‐1, kidney injury molecule‐1; L‐FABP, liver‐type fatty acid‐binding protein; LMW, low molecular weight; NGAL, neutrophil gelatinase‐associated lipocalin; PENIA, particle‐enhanced nephelometric immunoassay.