Alkaline phosphatase improves predictive power of Cl/PO4 ratio for primary hyperparathyroidism
The chloride/phosphate ratio (Cl/PO4) combined with alkaline phosphatase (ALP) is a simple and effective predictor of primary hyperparathyroidism (PHPT) in a Chinese population, a new study shows.
Compared with normal controls, ALP and Cl/PO4 levels were significantly higher in patients with normocalcaemic PHPT (NPHPT; 107.0 vs 61.5 U/L; p<0.001; 2.6 vs 2.4; p=0.001) and hypercalcaemia PHPT (114 vs 61.5 U/L; p<0.001; 43.1 vs 29.9; p<0.001).
Stepwise multiple regression showed that Cl/PO4 was an independent risk factor for the hypercalcaemia PHPT (odds ratio [OR], 0.832; 95 percent CI, 0.769 to 0.900; p<0.001) and NPHPT (OR, 0.797; 0.667 to 0.951; p=0.012) after adjusting for confounders like age, BMI and sodium levels.
While Cl/PO4 alone (area under the receiver operating curve [ROC-AUC], 0.73; 0.587 to 0.899) was a good predictor for NPHPT, including ALP in the model significantly increased predictive power (ROC-AUC, 0.913; 0.744 to 1.000).
The combined model also had greater specificity and sensitivity (83 and 94 percent, respectively) than CL/PO4 (80 and 73.7 percent, respectively) and ALP (66 and 94.7 percent, respectively) alone.
CL/PO4 alone was also a good predictor in the hypercalcaemia PHPT group (ROC-AUC, 0.897; 0.851 to 0.942). Including ALP in the model similarly increased its predictive value (ROC-AUC, 0.932; 0.897 to 0.966).
Sensitivity and specificity of the combined model (98 and 92.8 percent, respectively) were again greater than the models with Cl/PO4 (88.9 and 80 percent, respectively) and ALP (67.3 and 92 percent, respectively) alone.
The study included 172 PHPT patients categorized as having either NPHPT (n=19; mean age 59.1±14.3 years; 26.3 percent male) or hypercalcaemic PHPT (n=153; mean age 56.3±16.0 years; 21.6 percent male).
Exclusion criteria included vitamin D deficiency, secondary hyperparathyroidism, patients without surgery, renal diseases and use of diuretics among others.
A parallel control group of 50 normal, healthy individuals (mean age 45.5 years; 60.0 percent male) was also established.