Calcium-Phosphate Lab Questions

Question 1

A 56-year-old woman complains of fatigue. According to her medical records, she has hypertension, peptic ulcer and nephrolithiasis.

Laboratory findings:
serum Ca: 2.8 mmol/l
serum phosphate: 0.6 mmol/l
serum ALP: 450 U/l
*DEXA scan: T-score of –2.8 SD on the hip and forearm.
What test(s) would you order to determine the exact cause of her disease?

*DEXA = Dual Energy Xray Absorptiometry

Answer 1

• [ALP] ↑ - Here it means Osteoblast Activity ↑
• Osteoporotic T score :DEXA measured compared with young population (~30).
• [Calcium] ↑ , [Phosphate] ↓ - PTH Effect ↑
• [Calcium] ↑ is →Gastrin→[HCl]↑→Peptic Ulcers
• Primary Hyperparathyroidism : Intrinsic Hyperactivity of the parathyroid glands due to adenoma/hyperplasia. Leads to Secondary Osteoporosis.
• Additional Tests: Scintography(99mTc), US , FNA, PTH and VitD level.

Question 2

A 68-year-old nonsmoking man has been complaining of progressive weakness for 2 weeks. In addition to these symptoms he has developed intermittent cough, pleuritic chest pain and exertional dyspnea for 6 days. In the last weeks he frequently experienced nausea and vomited several times. Medical history reveals no
hypertension or coronary artery disease. He has a long history of heartburn – he takes
regularly antacids and drinks 1–2 l milk a day. Laboratory findings:
serum Ca: 2.8 mmol/l
serum phosphate: 1.8 mmol/l
BUN: 24 mmol/l
HCO3–: 38 mmol/l
PTH and vitamin D: normal.
What is the most likely diagnosis?

Answer 2

• Probable diagnosis: Milk-Alkali Syndrome - Antacid negative charge → high Ca absorption from Milk = Hypercalcemia.
• [BUN] ↑ and [Phosphate] ↑ - Sign of Kidney Failure due to Neprhocalcinosis
• [Bicarbonate]↑ → Mild Metabolic Alkalosis
• Hypercalcemia → Lung Calcifications → Pleuritic Chest Pain, Cough and Dyspnea
• Normal PTH and VitD rules out other causes.

Question 3

A 35-year-old woman is complaining about frequent muscle cramps. She was admitted to the hospital after having a convulsion. She had thyroidectomy 3 months
ago and she is on thyroid hormone substitution since then. Physical examination revealed a positive Chvostek’s sign and Trousseau’s phenomenon. Laboratory findings:
serum Ca: 1 mmol/l
serum phosphate: 2.0 mmol/l
serum ALP 140 U/l
What is your diagnosis? What further test(s) would you order to support your
diagnosis?

• Chvostek Sign: Masseter Twiches when touched.
• Trousseau’s Phenomenon: Forearm Muscles Spasm when BP cuff is used.

Answer 3

• Probable Diagnosis: PTH Deficiency due to Thyroidectomy (cause of +Parathyroids removal)
• Severe Hypocalcemia - Risk of Laryngeal Spasm, Muscle Excitability ↑ → Chvostek Sign, Trousseau’s Phenomenon.
• Hyperphosphatemia → Fails to Induce PTH↑ this time (Normal ALP)
• Additional: PTH, VitD levels, scintography
• Tx: First Ca IV then VitD IV

Question 4

A 66-year-old woman felt a sharp, sudden lumbar pain as she was lifting a bag of groceries out of the supermarket cart. An X-ray taken in the emergency department showed a compression fracture of L1 vertebra.

Laboratory findings:
serum Ca: 2.4 mmol/l
serum phosphate: 1.1 mmol/l
What is your diagnosis? What further tests would you order?

Answer 4

• Diagnosis: Pathological Fracture; ← Primary (Postmenopausal) Osteoporosis (during normal activity)
• Postmenopausal Osteoporosis : Estrogen↓ → OPG↓ → Osteoclast Activity↑
• Normophosphatemia and Normocalcemia is typical for Primary Osteoporosis
• Additional tests: DEXA, Estrogen levels and [PTH, ALP, Urinary Calcium] should be normal

Question 5

A 60-year-old diabetic woman has been on hemodialysis for 15 years. She recently started to complain of cardiac pain. She has no history of cardiac illness. Physical examination reveals pale, grey-yellow colored skin, but nothing else remarkable.
Exercise electrocardiogram shows ST-T alterations. Laboratory findings:
ALAT: 45 U/l
ASAT: 52 U/l
ALP: 120 U/l
serum creatinine: 180 μmol/l
serum Ca: 2.1 mmol/l
serum phosphate: 2.8 mmol/l
serum PTH: elevated
What is the possible diagnosis?? What further tests would you perform?

Answer 5

• _Renal Failure (**3 Mechanisms)→ Secondary Hyperparathyroidism_ (**See Image)
• [ASAT]↑: Organ Damge
• Renal Failure: [Creatinine]↑= GFR↓, [Phosphate]↑
• ST-T ECG Changes due to Hypocalcemia (Ca-P complex) or Hyperkalemia
• Renal Failure → EPO ↓ → Anemia and Paleness
• Normalizing Ca: If PTH level stays high = Tertiary Hyperparathyroidsim
• Additional Tests: DEXA, Troponin T, K+, US, 99mTc,

Question 6

A 65-year-old man complains of frequent urination and urinary retention. There is no macrosopic hematuria, urination is not painful. He complains of recurrent abdominal pain in the last weeks. Laboratory findings:
serum Ca: 3.5 mmol/l
serum Phosphate: 2 mmol/l
BUN: normal
What is the possible diagnosis? What further tests would you perform to support your diagnosis?

Answer 6

• Prostate Carcinoma with Bone Metaplasia - This causes cycles of Hypercalcemia and Hypocalcemia due to the osteolytic Lesions and PTH response. PTHR or PTHrP could also be up.
• Severe Hypercalcemia → NMJ Excitability↓, risk of coma or cardiac arrest. Reccurent abdominal pain could link to it by GI Tonicity↓.
• BUN Normal = Kidney functions well
• Diagnosis is Only by Core Needle Biopsy ,Screening - Digital Rectal Examination / PSA. Lesion Conformation: ALP and PTH +CT/US.