Calcium is measured to evaluate function and adequacy of a physiologic processes. Calcium plays a critical role in several body functions such as, coagulation pathways, bone health, nerve conduction, and other functions. It is important whenever you are evaluating laboratory results that you look at the whole picture of the person, including medications, other laboratory studies and health history. One value is not a stand alone result. There are many factors that effect calcium results.
Factors that effect calcium results: (not an all inclusive list)
The two most common issues following Weight loss Surgery or Duodenal Switch may be albumin level and Vitamin D level. Please see past blogs on Vitamin D. Magnesium may also play a role in a Duodenal Switch patient.
The most common calcium result drawn is the total calcium level. Laboratory results may not explicitly label it as such, however, it measures the calcium that is bound to protein. Ionized calcium is the free calcium that is representative of the true total calcium. Ionized Calcium can be measured by ordering specific lab. Alternatively, the Ionized calcium can be calculated by the following formula: Corrected calcium mg/dL = (0.8 * (Normal Albumin – Pt’s Albumin)) + Serum Ca ) or use the calculator at the bottom of this post.
The low Albumin level accounts for the low calcium level. This may be the reason for a patient with a low albumin/protein level, also having their calcium level reported as low. However, when adjusted for the protein deficiency the corrected calcium comes into normal range. Video of Trouseau’s sign of a patient with calcium deficiency.
The first step in a patient who has low calcium reported, is to make sure their protein and albumin levels are normal, along with Vitamin D.
Calcium levels are managed by two processes major regularly hormones and influencing hormones. Controlling or major regulatory hormones include PTH, calcitonin, and vitamin D. In the kidney, vitamin D and PTH stimulate the activity of the epithelial calcium channel and the calcium-binding protein (ie, calbindin) to increase calcium absorption. Influencing hormones include thyroid hormones, growth hormone, and adrenal and gonadal steroids.
Corrected calcium = 0.8 * (4.0 – serum albumin) + serum calcium
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