Proximal Renal Tubulopathy (PRT)

Indications and Tests for Proximal Renal Tubulopathy (PRT)

Indications for proximal renal tubulopathy tests

Proximal renal tubulopathy tests(iv), including

Replace TDF by non-tenofovir drug or TAF* alternative drug if:

  • Progressive decline in eGFR(i) & eGFR ≤ 90 mL/min & no other cause and/or
  • Confirmed hypophosphataemia(ii) and/or
  • Confirmed increase in UP/C(iii)
  • Renal insufficiency even if stable (eGFR ≤ 60 mL/min)
  • Tubular proteinuria(v)
  • Blood phosphate and urinary phosphate excretion(vi)
  • Blood glucose and glucosuria
  • Serum bicarbonate and urinary pH(vii)
  • Blood uric acid level and urinary uric acid excretion(viii)
  • Serum potassium and urinary potassium excretion
  • Confirmed proximal renal tubulopathy with no other cause

 

  1. For eGFR: use CKD-EPI formula. The abbreviated MDRD (Modification of Diet in Renal Disease) or the Cockcroft-Gault (CG) equation may be used as an alternative, https://www.chip.dk/Tools-Standards/Clinical-risk-scores
  2. Serum phosphate < 0.8 mmol/L or according to local thresholds; consider renal bone disease, particularly if alkaline phosphatase increased from baseline: measure 25(OH) vitamin D, PTH
  3. UP/C in spot urine, detects total urinary protein, including protein of glomerular or tubular origin. The urine dipstick analysis primarily detects albuminuria as a marker of glomerular disease and is inadequate to detect tubular disease
  4. It is uncertain which tests discriminate best for TDF renal toxicity
    Proximal tubulopathy is characterised by: proteinuria, hypophosphataemia, hypokalaemia, hypouricaemia, renal acidosis, glucosuria with normal blood glucose level. Renal insufficiency and polyuria may be associated. Most often, only some of these abnormalities are observed
  5. Tests for tubular proteinuria include retinol binding protein, α1- or β2-microglobulinuria, urine cystatin C, aminoaciduria.
  6. Quantified as fractional excretion of phosphate (FEPhos): (PO4(urine) / PO4(serum) / (Creatinine(urine) / Creatinine(serum) in a spot urine sample collected in the morning in fasting state. Abnormal > 0.2 (> 0.1 with serum phosphate < 0.8 mmol/L)
  7. S-bicarbonate < 21 mmol/L and urinary pH > 5.5 suggests renal tubular acidosis
  8. Fractional excretion of uric acid (FEUricAcid): (UricAcid(urine) / UricAcid(serum) / (Creatinine(urine) / Creatinine(serum) in a spot urine sample collected in the morning in fasting state; abnormal > 0.1

* Particularly if eGFR > 30 mL/min, as there are limited data on use of TAF with eGFR ≤ 30 mL/min