TmP/GFR (Renal Phosphate Threshold)
TmP/GFR renal phosphate threshold (Payne 1998): tubular reabsorption of phosphate (1 − urine P × serum Cr / (serum P × urine Cr)) times serum P, using the Payne hyperbolic branch when TRP > 0.86.
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Example
- Serum phosphate
- 1.2
- Urine phosphate
- 15
- Serum creatinine
- 0.09
- Urine creatinine
- 9
Result: TmP/GFR 1.05 (in the serum-phosphate unit) — TRP 0.875, hyperbolic branch.
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What the result means
- Interpretation
- TmP/GFR carries the serum-phosphate unit; adult reference ≈ 0.80–1.35 mmol/L (2.5–4.2 mg/dL). Low = renal phosphate wasting (hyperparathyroidism, FGF23 excess); high = retention.
What you enter
- Serum phosphate (shared phosphate unit)
- Urine phosphate (shared phosphate unit)
- Serum creatinine (shared creatinine unit)
- Urine creatinine (shared creatinine unit)
How this is calculated
- Formula
- TRP = 1 − (U_P × S_Cr)/(S_P × U_Cr). TmP/GFR = TRP × S_P when TRP ≤ 0.86 (linear), else (0.3 × TRP)/(1 − 0.8 × TRP) × S_P (Payne hyperbolic).
Payne RB. Renal tubular reabsorption of phosphate (TmP/GFR): indications, interpretation and clinical usefulness. Ann Clin Biochem. 1998;35(Pt 2):201-206. Nomogram: Walton RJ, Bijvoet OLM. Lancet. 1975;2(7929):309-310. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.