Determination of NTx in second-morning urine: a proposal for the standardization of morning urine collection.
According to the instruction manual from the producer of kits for determining the levels of aminoterminal telopeptide of type I collagen of organic bone matrix (NTx), the time of the collection of second-morning urine is arbitrary, i.e., a patient can urinate anytime within the period from about 6 to 8:30 a.m. This time interval is within the period of change in the circadian rhythm of the NTx excretion (maximum excretion with transition into fast decrease of excretion). Therefore, we considered it appropriate to standardize the conditions for the collection of second-morning urine and proposed applying the so-called 2-hour morning urine NTx2 (from 6 to 8.00 a.m. after an overnight fast). We examined 48 female patients aged 33-65 years with primary or secondary osteopenia or osteoporosis (all patients had normal renal functions). In these patients we determined NTx (Osteomark, OSTEX, USA) in standardly used 24-hour urine (NTx24) and in the proposed 2-hour morning urine (NTx2).


OBJECTIVE
1) To find a mathematical character for the dependence of values of dependent variable NTx2 on independent variable NTx24 and to evaluate the statistical significance of this dependence; 2) to compare the ratio of the widths of 95% confidence intervals (C. I.) for NTx2 and NTx24 in patients (index: IO) with the ratio of the widths of reference limits for NTx in arbitrary second-morning urine (NTx2ostex) and in 24-hour urine (NTx24ostex) in healthy women (index: IR); 3) to evaluate the proposed 2-hour urine for the determination of NTx.


METHODS
Stochastic and deterministic linear regressive analysis. Index of 95% C. I., index of reference limits.


RESULTS
A statistically significant (P < 0.01) regressive dependence (r2 = 0.781) was found between the values of NTx24 and NTx2. The index for the widths of reference limits (IR) was 1.5 times greater than the index for osteopenic and osteoporotic patients (IO), meaning that the scatter of the NTx2ostex values was greater than NTx2 in the proposed 2-hour urine.


CONCLUSIONS
Based on the statistically significant linear regressive dependence between NTx24 and NTx2 values, it is possible to use the proposed 2-hour morning urine to determine NTx levels in women. The introduction of 2-hour morning urine NTx2 could decrease the fluctuation range of NTx values in repeated examinations and in comparison with the determination of NTx2ostex in a random second-morning urine sample could make its values more accurate.
Wendlová
J
J
Osteological Clinic, Derer's University Hospital and Polyclinics, and the Department of Ergonomics and Biometry, Institute of Preventive and Clinical Medicine, Bratislava, Slovakia. jaroslavaw@kiwwi.sk
Mikulecký
M
M
D000328:Adult; D000367:Age Factors; D000368:Aged; D001857:Bone Matrix / Q000737:chemistry*; D002940:Circadian Rhythm / Q000502:physiology; D024042:Collagen Type I / Q000652:urine*; D005260:Female; D006801:Humans; D008875:Middle Aged; D015663:Osteoporosis, Postmenopausal / Q000175:diagnosis / Q000652:urine; D010446:Peptide Fragments / Q000652:urine*; D011933:Reagent Kits, Diagnostic; D012016:Reference Values; D013048:Specimen Handling / Q000592:standards*
D024042:Collagen Type I; D010446:Peptide Fragments; D011933:Reagent Kits, Diagnostic