5
Table 3. Laboratory Indicators of Proximal Tubular
Dysfunction (continued)
Abnormality
Definition of
Abnormality Comment
Tubular maximum
for phosphate
corrected for GFR
(TmP/GFR)
Lower than
reference value
(normal, 2.8-4.4
mg/dL)
Assess renal phosphate handling
independent of plasma phosphate and
renal function
Fractional excretion
of uric acid (FE
UA
)
<15% is normal and
>20% is abnormal
• Increased FE
UA
in the setting of normal
kidney function is of more clinical
relevance than when kidney function
is impaired
• Upward trend in urinary uric acid
wasting is strongly suggestive of
proximal tubular dysfunction
Urine albumin-
to-protein ratio
(uAPR)
uAPR <0.4 suggests
predominantly
tubulointerstitial
disease, whereas
uAPR >0.4 suggests
predominantly
glomerular disease
• Based on theory that albumin accounts
for a lower proportion of protein in
urine when loss is from tubular as
opposed to glomerular disease
• Evaluated only in individuals
with urine protein/creatinine ratio
>200 mg/g
Other laboratory indicators of proximal tubular dysfunction
Nonspecific
indicators
• Proteinuria/
albuminuria
• Hematuria
Investigational markers or markers with
limited clinical availability
• Aminoaciduria
• Urinary α-1 microglobulin
• Urinary β-2 microglobulin
• Urinary retinol binding protein
• Urinary cytochrome C
• Urinary cystatin C
