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Calcium-Phosphate Product Calculator

Get the calcium × phosphate product instantly.

Result

44.2 mg²/dL²

How it is calculated

The calcium-phosphate product is a single multiplication: Product = Ca × P, where Ca is serum calcium and P is serum phosphate, both in mg/dL. The result is shown in mg²/dL² with one decimal place, so 44.16 appears as 44.2. Both values must be above zero, and empty, zero or negative entries return no result. The tool does not convert units. Many labs outside the US report calcium and phosphate in mmol/L, and those values must be converted to mg/dL before multiplying (roughly 4 times for calcium and 3.1 times for phosphate). It also does not mark the product as high or normal; the threshold around 55 comes from the general guidance and is only one input to a clinician's judgement.

Worked example

A kidney panel shows serum calcium 9.2 mg/dL and phosphate 4.8 mg/dL. Multiply the two: 9.2 × 4.8 = 44.16. The tool rounds to one decimal and shows 44.2 mg²/dL². This is below the figure of about 55 mentioned in the general guidance above. That comparison alone does not say a person is safe, because the calcium and phosphate levels, PTH and the clinical picture still need to be reviewed by the treating team.

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Common mistakes

  • Entering mmol/L values. Calcium 2.3 and phosphate 1.5 mmol/L give 3.5, which looks far too low, so convert both to mg/dL first.
  • Entering a calcium that has not been corrected for albumin when your lab or clinician uses the corrected value. The tool multiplies exactly what you type.
  • Reading 44.2 mg²/dL² as if the unit were mg/dL. It is a product of two concentrations, so the square units are part of the answer.
  • Comparing results from different units or labs in the same trend. Keep the same units for every entry.
  • Using this number alone. Calcium and phosphate can each be abnormal while the product looks acceptable, so look at the two values separately as well.

Sources

About this calculator

The calcium-phosphate product (Ca × P, also written Ca × PO4) is a simple multiplication of a patient's serum calcium (mg/dL) by serum phosphate (mg/dL) used in nephrology to gauge the risk of ectopic calcification. It is a core marker in CKD-MBD (chronic kidney disease–mineral and bone disorder), the syndrome of disturbed calcium, phosphate, PTH and vitamin D metabolism that develops as kidney function declines.

Nephrologists and dialysis teams track Ca × P because when the product climbs above roughly 55 mg²/dL², soluble calcium phosphate can precipitate out of the blood and deposit in soft tissue, blood vessels, and heart valves — a process called vascular and metastatic calcification that is linked to higher cardiovascular risk in dialysis patients. The older K/DOQI guideline (2003) used this threshold, alongside individual calcium and phosphate targets, to guide phosphate-binder and vitamin-D-analog management in end-stage renal disease; current KDIGO CKD-MBD guidance (2017 update) no longer sets a Ca × P target and assesses calcium and phosphate separately.

Multiply serum calcium by serum phosphate from the same lab report and the product appears at once, a reference point for clinicians and patients to read alongside the full CKD-MBD panel (PTH, vitamin D, alkaline phosphatase), not on its own.

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