Synonyms

Renal tubular maximum reabsorption rate of phosphate to glomerular filtration rate

Clinical Indications

Conditions that cause phosphate redistribution (e.g. glucose infusion, respiratory alkalosis) also increase renal phosphate loss, so if hypophosphataemia persists, a low (fasting) TmP/GFR indicates the need for phosphate replacement. In the treatment of severe phosphate deficiency, TmP/GFR can be used as an indicator of intracellular repletion.

The measurement of TmP/GFR (together with plasma 1,25-DHCC) is required for diagnosis of X-linked hypophosphataemic rickets and hereditary hypophosphataemic rickets with hypercalciuria. Measurement of TmP/GFR and 1,25-DHCC are central to the diagnosis of oncogenic osteomalacia

Test Includes

Serum and urine phosphate and creatinine. TmP/GFR is calculated from these parameters

Request Form

Combined Pathology Blood form (Yellow/Black)

Availability

On request.

Patient Preparation

Patient should be fasted (overnight if possible). The overnight urine is discarded. The next untimed urine is collected and a blood specimen is taken.

Turnaround Time

Same day

Specimen

Fasting serum/plasma and spot urine

Volume

2 ml

Container

Yellow top (SST) tube or Paediatric lithium heparin tube. Plain universal for urine.

Lab. Handling

Aliquot and store at 4C

Causes for Rejection

 Unlabelled samples. Not collected fasting.

Reference Range

Adult: 0.80 - 1.35 mmol/L. Age-related reference ranges.