Laboratory Evaluation in Osteoporosis
Diagnosis of osteoporosis is primarily done by measuring bone mineral density. In addition to this, certain laboratory tests are also required to be performed in all patients.
For an uncomplicated patient with osteoporosis, a lab workup would be a chemistry panel (electrolytes, bicarbonate, creatinine, albumin, calcium, alkaline phosphatase), CBC, phosphate, TSH and 24-hour urine calcium. Males should have testosterone measured. The main purpose of laboratory tests is to check for secondary causes of osteoporosis such as cases of renal or hepatic failure, anemia, acidosis, hypercalciuria, and abnormalities of calcium/phosphate.
Complete blood count is an indicator of general health including anaemia, protein nutrition, immune status etc. Also, bone mineral density is also influenced by several factors such as age, body weight, co-morbid conditions some of which can influence blood counts. Anemia may indicate multiple myeloma.
Elevated calcium suggests hyperparathyroidism and decreased calcium suggests malabsorption or vitamin D deficiency/resistance. Vitamin D is often recommended for patients who have osteoporosis.
Vitamin D deficiency is associated with osteoporosis and various clinical conditions including cardiovascular diseases, autoimmune diseases and cancer risk. Two laboratory tests for vitamin D that are available are 25-hydroxy vitamin D [25(OH)D], and1,25-dihydroxyvitamin D. Vitamin D status is commonly assessed by measuring the serum 25(OH)D levels. The 25(OH)D metabolite provides a measure of the vitamin D originating from both dietary/supplement sources and that produced from the skin.
Alkaline phosphatase is an enzyme found in the blood. The total ALP is often a routine part of blood tests. The normal levels of ALP with people are various by age, blood type, gender and pregnancy. Abnormal concentrations of ALP in blood generally indicate issues with liver, gall bladder, or bones. The ALP test can be used for diagnosis of bone problems such as rickets, osteomalacia and Paget’s disease. Measurement of Bone specific Alkaline Phosphatase is applied as the assistance for the management of osteoporosis in premenopausal and postmenopausal women.
There are a number of secondary causes of osteoporosis such as hypogonadism or hyperparathyroidism, which are treatable, and renal failure, which should be considered more seriously. Chronic liver diseases also play an important role among secondary factors of osteoporosis. Various studies have demonstrated associations between hepatic disease and osteoporosis or decreased bone mass. Low bone mass has been observed in various liver disorders.
Additional laboratory tests such as parathyroid hormone, thyroid-stimulating hormone, and serum protein electrophoresis may be indicated after the initial evaluation. Parathyroid hormone is not routinely checked because it is expensive, but when the calcium is abnormal or the patient has serious osteoporosis without other explanation then it should be measured. Protein electrophoresis should be done whenever a patient presents with new fractures. Both serum and urine tests should be done because some patients with myeloma have abnormalities in only one.
Sprue tests, such as antibodies to tissue transglutaminase, are indicated in a patient with low urine calcium, signs of diarrhoea and weight loss, or unexplained anemia with osteoporosis. Celiac sprue can cause osteoporosis without any intestinal complaints, although that is somewhat unusual.
Besides imaging techniques, an alternative is essential for early and accurate diagnosis of osteoporosis since correct and early diagnosis of osteoporosis helps in better management. Several biomarkers have been investigated in the past decade that have been used in measuring bone remodelling.
These are divided into three categories as follows:
I.Markers of Bone Resorption
a.In blood -
ii.Cathepsin K (CTSK)
iii.Bone Sialoprotein (BSP)
iv.Pro-collagen type 1 C-terminal portion (S-CTX)
v.Tartarate resistant acid phosphatase (TRACP)
b.In Urine –
iv.Amino terminal portion of pro-collagen 1 (U-NTX)
v.Carboxy terminal portion of pro-collagen 1 (U-CTX)
II.Markers of Bone Formation
ii.Total Alkaline Phosphatase
iii.Pro-collagen Type 1 amino terminal propeptide (P1NP)
iv.Pro-collagen Type 1 carboxy terminal propeptide (P1CP)
III.Regulators of Bone Turnover
i.Receptor activator of NF-κB ligand (RANKL)
iii.Others : Dickkopf-1 (DDK-1), Sclerostin
Although bone markers may not be used to diagnose osteoporosis, they are often required to aid in predicting the future rate of bone loss and risk of osteoporotic fractures. They are also useful in monitoring response to therapy.
Levels of bone turnover markers are age dependant. The levels are usually higher in men than in women. In women, the levels are lowest between 35-45 years age range usually, showing an elevation following menopause. Marker levels are elevated during pregnancy and lactation and tend to normalize after a few months following weaning The ethnic background of the patient is also to be considered since data suggest that the Caucasians usually have lower levels as compared to their age and sex matched adult counterparts. It is very important to consider certain factors while interpreting biomarker levels:
1. They follow circadian rhythm (peak levels observed early morning hours and tapering off during the day).
2. Seasonal variation.
3. Physical Exercise.
5. Phase of menstrual period in women.
If measurements of bone markers are properly conducted, in experienced facilities, they can contribute to a better appraisal of the underlying pathophysiological process and, in some cases, to confirm either adherence to treatment or to predict, to some extent, the long-term efficacy of the treatment.
There is increasing evidence that the best solution may be a panel of biomarkers, covering the range of physiological effects, or a combination of tissue biomarkers with other parameters (eg, imaging/USG) into single diagnostic tests. A well-selected panel of biomarkers may also assist in identifying the patients who are most likely to respond. Thus, targeting responders would reduce the cost of treatment by eliminating redundant prescriptions and improving benefits for patients. The ideal panel should include, for example, biomarkers of turnover, synthesis and degradation and tissue-specific biomarkers.