Walton and Bijvoet developed a nomogram for predicting a patient's renal threshold for phosphate. The authors are from University Hospital Leiden in the Netherlands.
(1) serum phosphorus in mg/dL over the range of 1 to 5 mg/dL
(2) ratio of phosphate to creatinine clearance over a range 0.1 to 1.0 (= fractional phosphate excretion)
(3) TRP (tubular reabsorption of phosphate)
ratio of phosphate to creatinine clearance =
= 1 - (tubular reabsorption of phosphate) = 1 - (TRP) =
= ((urine phosphate in mg/dL) * (serum creatinine in mg/dL)) / ((urine creatinine in mg/dL) * (serum phosphate in mg/dL))
• The conversion factors for mg/dL to mmol/L is 0.4 in the nomogram, but according to Tietz it is 0.323.
predicted threshold in mg/dL for clearance ratio from 0.1 to 0.2 =
= (serum phosphate) * (1.225 - (2.55 * (ratio)) + (2.5 * ((ratio)^2)))
predicted threshold in mg/dL for clearance ratio from 0.2 to 1.0 =
= (serum phosphate) * (1 - (ratio))
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Specialty: Nephrology, Clinical Laboratory