Normal Serum Phosphorus Range in Adults
The normal serum inorganic phosphorus (phosphate) concentration range in adults is 2.5 to 4.5 mg/dL (0.81 to 1.45 mmol/L), with specific reference values determined by local laboratory standards. 1
Standard Reference Ranges
The normal phosphorus range varies slightly depending on the clinical context and population:
- General adult population: 2.5-4.5 mg/dL (0.81-1.45 mmol/L) 1
- Higher levels are physiologically normal in childhood, adolescence, and pregnancy 1
Clinical Context: Chronic Kidney Disease
In patients with chronic kidney disease, target phosphorus ranges differ from the general population and are stratified by disease stage:
- CKD Stages 3-4 (GFR 15-59 mL/min/1.73 m²): Maintain serum phosphate at 2.7-4.6 mg/dL (0.87-1.49 mmol/L) 2
- CKD Stage 5 (dialysis patients): Maintain serum phosphate between 3.5-5.5 mg/dL (1.13-1.78 mmol/L) 2
Guidelines recommend maintaining serum phosphate concentrations within the normal range according to local laboratory reference values for patients with advanced CKD (GFR <45 mL/min/1.73 m²). 2
Important Clinical Considerations
Why Normal Range Matters for Mortality and Morbidity
- Elevated phosphorus levels are associated with increased mortality, vascular calcification, and valvular calcification, particularly in CKD populations 2
- Even within the normal range, higher phosphorus concentrations (3.6-4.0 mg/dL and >4.0 mg/dL) are associated with significantly increased coronary artery calcification in subjects with normal kidney function 3
- Lower phosphorus levels within the normal range (2.0-2.49 mg/dL) are paradoxically associated with higher 30-day and 90-day all-cause mortality and increased hospitalization rates 4
Laboratory Screening Recommendations
- Measure serum phosphate at least once in adults with GFR <45 mL/min/1.73 m² (CKD stages G3b-G5) to establish baseline values 2
- In large cohorts (NHANES and KEEP) of participants with GFR <45 mL/min/1.73 m², phosphorus values were within normal range in 87-90% of patients 2
Common Pitfalls to Avoid
- Do not assume all "normal" phosphorus levels are equally safe: Even high-normal values (>3.6 mg/dL) may increase cardiovascular calcification risk in patients with normal kidney function 3
- Do not target the lower end of normal indiscriminately: Very low-normal phosphorus levels (2.0-2.49 mg/dL) are associated with worse outcomes and higher mortality 4
- Recognize that phosphorus regulation involves multiple hormones: PTH, FGF23, and active vitamin D all play critical roles in maintaining serum phosphate within the normal range 5
- Consider phosphorus source when making dietary recommendations: Processed foods contain highly bioavailable phosphate additives that are absorbed more efficiently than naturally occurring phosphates in fresh foods 2