A phosphorus- Serum test, performed like any blood test, is done to determine if you have high or low phosphorus. Either too low or too high phosphorus levels can lead to health problems. The test helps in assessing if you have any Kidney or bone disease or have any problems with glands like the parathyroid glands. This also helps to find out reason for abnormal vitamin D levels. The amount of phosphorus differs in adults and children. The lab report generated will give you standard value range for your age group and gender and also your current phosphorus levels.