Symptoms or Clinical Syndromes Associated with Primary Hyperparathyroidism,with Estimated Incidence
Urologic: nephrolithiasis, 30%-40% (21%-81%); renal failure
Skeletal: 15%-30% (6%-55%); osteoporosis, fracture, osteitis fibrosa cystica
Gastrointestinal: peptic ulcer, 15% (9%-16%); pancreatitis, 3% (2%-4%)
Neurologic: weakness, 25% (7%-42%); mental changes 25% (20%-33%)
Hypertension: 30%-40% (18%-53%)
Multiple endocrine neoplasia syndrome: 2% (1%-7%)
Asymptomatic hypercalcemia: 45% (2%-47%)
*Numbers in parentheses refer to literature range.
About 5% (literature range, 2%-10%) of patients with renal stones have PHPT. Laboratory tests. Among nonbiochemical tests, the hemoglobin level is decreased in less than 10% of cases (2%-21%) without renal failure or bleeding peptic ulcer. A large number of biochemical tests have been advocated for diagnosis of PHPT. The classic findings on biochemical testing are elevated serum calcium, PTH, and alkaline phosphatase levels and a decreased serum phosphate level.Serum calcium (total serum calcium). Most investigators consider an elevated serum calcium level the most common and reliable standard biochemical test abnormality in PHPT. Even when the serum calcium level falls within the population reference range, it
can usually be shown to be inappropriately elevated compared with other biochemical indices. However, PHPT may exist with serum calcium values remaining within the reference range; reported incidence is about 10% of PHPT patients (literature range,0%-50%). Normocalcemic PHPT has been defined by some as PHPT with at least one normal serum calcium determination and by others as PHPT in which no calcium value exceeds the upper reference limit. Some of the confusion and many of the problems originate from the various factors that can alter serum calcium values in normal persons, as listed here.
1. Reference range limits used. Reference range values may be derived from the literature or from the reagent manufacturer or may be established by the laboratory on the local population. These values may differ significantly. For example, the values supplied by the manufacturer of our calcium method are 8.7-10.8 mg/100 ml (2.17-2.69 mmol/L), whereas our values derived from local blood donors (corrected for effects of posture) are 8.7-10.2 mg/100 ml (2.17-2.54 mmol/L).
2. The patient's normal serum calcium value before developing PHPT compared with population reference values. If the predisease value was in the lower part of the population reference range, the value could substantially increase and still be in the upper part of the range.
3. Diet. A high-calcium diet can increase serum calcium levels up to 0.5 mg/100 ml. A high-phosphate diet lowers serum calcium levels, reportedly even to the extent of producing a normal calcium value in PHPT.
4. Posture. Changing from an upright to a recumbent posture decreases the serum calcium concentration by an average of 4% (literature range, 2%-7%). A decrease of 4% at the 10.5 mg/100 ml level is a decrease of 0.4 mg/100 ml. Therefore, reference ranges derived from outpatients are higher than those established in blood donors or others who are recumbent. This means that high-normal results for outpatients would appear elevated by inpatient standards.
5. Tourniquet stasis. Prolonged stasis is reported to produce a small increase in serum calcium and total protein values.
6. Changes in serum albumin concentration (discussed under ionized calcium).
7. Laboratory error or, in borderline cases, usual laboratory test degree of variation.
