case_images: PMC11347025_01
case_images: Impact of calcium-binding proteins on overall calcium distribution in plasma. In normal conditions (middle), approximately 50% of the calcium in blood is present as free ions, termed "ionized calcium"; about 40% of the calcium is bound to proteins (e.g. albumin); and the remainder of calcium is bound to anions, such as citrate and phosphate. The balance between these fractions is dependent on pH, the concentration of calcium-binding proteins, and the concentration of involved anions. Disruptions in this balance can result in temporary shifts in the fraction size, for instance, due to changes in the concentration of calcium-binding proteins, either due to loss of albumin (hypoalbuminemia), or by additional presence of a calcium-binding protein. Homeostatic mechanisms will respond to keep the (biologically important) ionized calcium fraction constant. As a result, the total calcium is either decreased or increased, leading to pseudohypocalcemia (left): a combination of decreased total calcium and normal ionized calcium (e.g., caused by hypoalbuminemia) or pseudohypercalcemia (right): a combination of increased total calcium and normal ionized calcium (caused by a larger protein-bound fraction, e.g., due to the presence of a calcium-binding paraprotein).
case_images: CRIHEM2024-8844335.001.jpg
case_images: PMC11347025_01_CRIHEM2024-8844335.001.jpg
case_images: fig1
case_images: In blood, calcium is present in the following three distinct fractions: "free" ionized calcium (the biologically active fraction), bound to protein (such as albumin), and complexed to anions such as citrate, phosphate, and lactate (Figure 1).
case_images: A calcium-binding plasma protein causes pseudohypercalcemia in the patient of interest, acting as a fully exploited calcium-binding reservoir. Recovery for total calcium (a) and recovery for ionized calcium (b) in plasma of the patient of interest (two different samples, two time points, and two months apart) and six controls with normal to high total calcium. Recovery is defined as the post-PEG treatment concentration of calcium as a percentage of the pretreatment calcium concentration (total calcium in (a) and ionized calcium in (b)). Bars represent the mean with SD. Statistical analysis (unpaired t-test) indicated a significant difference between patient and controls (***p  <  0.05) for total calcium (a) but no significant difference between patient and controls for ionized calcium (NS) (b). Increase in total calcium levels (c) and increase in ionized calcium levels (d) in plasma of the patient of interest (two different samples, two time points, and two months apart) and five controls after addition of 0, 0.3, 0.6, and 0.9 M calcium. Control samples were available plasma samples from five persons (different from the six controls in (a) and (b)), selected based on total calcium values, albumin values, and total protein levels within reference interval and kidney function with GFR > 70 ml/min/1.73 m2.
case_images: CRIHEM2024-8844335.002.jpg
case_images: PMC11347025_01_CRIHEM2024-8844335.002.jpg
case_images: fig2
case_images: Surprisingly, similar calcium increases were observed in patient and control plasma upon addition of the calcium-containing solution, both in total and ionized calcium (Figures 2(c) and 2(d)), indicating that the extra calcium-binding capacity of the monoclonal protein was already maximally used.
case_images: Calcium, hemoglobin and monoclonal protein levels in blood during patient follow-up and treatment. Total calcium and ionized calcium levels (a), hemoglobin levels, (b) and monoclonal paraprotein levels, and (c) in the patient's blood during follow-up and treatment over time, starting from the date of presentation. In (a), upper and lower limits of the reference interval for total calcium and ionized calcium are indicated in orange and in green, respectively. In (b), upper and lower limits of the reference interval of hemoglobin are indicated in orange.
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case_images: PMC11347025_01_CRIHEM2024-8844335.003.jpg
case_images: fig3
case_images: Plasma calcium parameters, hemoglobin level, and monoclonal paraprotein level were monitored over time (Figure 3). While total calcium levels were consistently high and above the reference interval, ionized calcium levels remained within the normal range, i.e., pseudohypercalcemia persisted (Figure 3(a)). Hemoglobin levels continued to be below the reference interval, only minimally declining after more than one year since presentation (Figure 3(b)). The monoclonal paraprotein steadily increased over time (Figure 3(c)). During the first cycle of treatment, the paraprotein level dropped from 45 to 15 g/L within four weeks (Figure 3(c)), with no significant changes in albumin levels or kidney function (data not shown). Within the same timeframe, the plasma total calcium level gradually dropped from 3.27 mmol/L to 2.51 mmol/L (which is within the normal range), whereas ionized calcium levels continued to be within the normal range (Figure 3(a)).