PHOSPHORUS, whole blood
fB-P ATK 8008

The primary portion, accounting for approximately 80-85%, of phosphorus in the body is situated within the bones in the form of hydroxyapatite (Ca10(PO4)6(OH)2). About 15% is found within cells, while only 1% is present in the plasma and extracellular fluid. Phosphorus performs a vital role in cellular energy metabolism through energy-rich molecules (ATP, ADP, AMP), as well as in the regulation of the body’s acid-base equilibrium. It also acts as a structural element in cell membrane phospholipids and in cellular genetic material. Furthermore, phosphorus plays a role in the metabolism of carbohydrates, proteins, and fats.

Phosphate metabolism is closely intertwined with calcium metabolism, both being regulated by parathyroid hormone (PTH), 1,25-(OH)2-vitamin D (calcitriol), and skeletal fibroblast growth factor 23 (FGF23). The kidneys play a crucial role in maintaining the body’s phosphorus balance, reacting promptly to fluctuations in phosphorus levels.

Plasma phosphate levels do not provide an accurate reflection of the body’s phosphorus reserves. Instead, measuring phosphate concentration in whole blood offers a more accurate representation of the body’s phosphorus status.


Assessment of phosphorus reserves in the body.


5 mL of lithium or sodium heparin blood. Mix the sample well. The tube must not contain any clots. Take trace element samples last in order to cleanse the sampling needle of possible trace element residues. If this is the only test requisition, first take one extra tube.

No fasting is needed. No trace element supplements 12 hours before sampling. The result is normalised to whole blood hematocrit (Hct) value (Complete Blood Count, B -CBC). The client should determine the hematocrit prior to shipping the sample and write the result on the test requisition.

The Hct is essential for interpretation of results. Without a measured Hct value, standard Hct is used.

Storage and delivery

Ship at room temperature on sampling day (shipping Mon-Thu). Store frozen over the weekend, ship at room temperature.

Method principle

ICP-MS, Accredited method

Turnaround time

10 weekdays

Reference ranges, calculated

women 9.3 – 13.4 mmol/L (Hct 0.39)
men 9.4 – 13.6 mmol/L (Hct 0.42) 

The Hct value affects the reference ranges. The same sample can be used to measure Cu, K, Mg, Mn, Se and Zn.

The reference areas have been calculated from the Mineral Laboratory Milan research database. Outliers that significantly differed from the reference distribution were excluded. A mid-percentile range of 90% has been established based on the refined dataset. The most recent update was in 2017.

Interpretation of results

Dairy and grain products, meat, fish, and eggs are notable dietary sources of phosphate. These sources are absorbed to a range of 60-70 percent. In the case of cereal products, phytate content can hinder phosphate absorption. Processed foods, including items like processed cheeses, meat products, and cola drinks, often contain added phosphate as additives. Remarkably, these additive phosphates are absorbed most efficiently, with nearly 100% absorption. The absorption of dietary phosphate occurs within the intestines.

Phosphorus deficiency can arise due to elevated urine excretion or reduced absorption within the intestines. The underlying causes of such disorders can be attributed to hereditary factors, kidney issues, intestinal diseases, or medication/toxin effects. Among severely ill individuals, particularly those in malnourished states like anorexia, alcoholism, or unbalanced diabetes, phosphate deficiency is common. Hyperparathyroidism, marked by excessive parathyroid hormone (PTH) production, elevates phosphate excretion into urine, leading to phosphorus deficiency. Acute phosphorus deficiency exhibits neuromuscular symptoms such as irritability, confusion, muscle weakness, and diminished consciousness levels. In the long term, chronic phosphorus deficiency contributes to osteomalacia and rickets.

The most prevalent cause of hyperphosphatemia is acute or chronic renal failure. In kidney failure scenarios, phosphorus intake surpasses urinary phosphate excretion, potentially causing excessive PTH secretion and secondary hyperparathyroidism due to hypocalcemia. This situation could impact the emergence of cardiovascular issues and increased mortality rates. Furthermore, sustained high intake of phosphate from processed foods, particularly those with added phosphates, in conjunction with low calcium intake, can pose a problem and trigger bone degradation. The maximum safe daily phosphorus intake is set at 3000 mg.


Last update 8.8.2023