<s>[INST] context: This child has :-


Hypocalcemia
Hyperphosphatemia
	Normal PTH levels


Option b & d can be ruled out because:-


In Vitamin D deficiency:- serum calcium is normal or slightly reduced (7.5 ­ 8 mg/dl); serum P043 is normal or slightly reduced, and parathormone levels are increased.
hypoxic-ischemic encephalopathy is not related to calcium and phosphate metabolism.


Now, we are left with Pseudohypoparathyroidism and hypoparathyroidism both of which have hypocalcaemia and hyperphosphatemia.
In Pseudohypoparathyroidism, there is an increased concentration of parathyroid most of the times. Thus, this option is also excluded.
Coming to hypoparathyroidism: As the name suggests, PTH is low in hypoparathyroidism. But, sometimes PTH may be in normal range (10-60 Pg/ml) and this is inappropriately normal PTH.
However, it is generally believed that 'Normal' levels of PTH in a patient with hypocalcaemia indicate 'inappropri­ately normal PTH' and relative Hypoparathyroidism should always be considered as the initial diagnosis. `Serum PTH levels should be related to the concurrent serum calcium. High PTH is the normal response to hypocalcaemia and therefore 'normal' PTH in a patient with Hypocalcaemia indicates relative Hypoparathyroidism' ­Practical Algorithms in Pediatric Endocrinology' by Hochberg (2007)/71.
Because normally hypocalemia is a potent stimulus for secretion of PTH, patients with intact parathyroid gland function should be expected to have high circulating levels of PTH, during hypocalcaemia episodes. Low levels of serum PTH and in some assays even inappropriately 'normal' levels despite hypocalcaemia should prompt consider­ation of various form of hypoparathyroidism' - Principles and Practice of Endocrinology & Metabolism ' by Beeker. [/INST] question: A 15 days old baby is brought to the hospital with complains of seizures.;Mood tests revealed serum Ca++ = 5 mg/dL, Phosphorous levels = 9mg/dL, and PTH levels 30pg/ml (normal range = 10–60 pg/ml). What is the most probable diagnosis? | options: A: Pseudohypoparathyroidism B: Vitamin D deficiency C: Hypoparathyroidism D: Hypoxic ischemic encephalopathy | answer: C </s>