Background: Shrunken pore syndrome (SPS), defined by cystatin C (CysC) based estimated glomerular filtration rate (eGFR _CysC ) < 60% of creatinine (Cr) based eGFR (eGFR _Cr ) in the absence of extrarenal influences on the plasma levels of CysC or Cr, is associated with a higher increase in mortality. SPS often causes reduced bone mineral density (BMD).

Objectives: In this study, relationship between BMD and SPS was investigated.

Methods: Patient with rheumatic diseases who were measured BMD with dual-energy X-ray absorptiometry and at the same time, CysC and Cr were also measured, were picked up. eGFR _CysC and eGFR _Cr, were calculated, and a patient group with SPS were recruited. Relationship between serum PTH and CysC, or Cr was evaluated with univariate linear regression analysis. Between the SPS groups and the other patient group, statistical difference was evaluated regarding sex, age, Cr, CysC, serum Cr-CysC ratio (Cr/CysC), serum calcium corrected with albumin (Ca), creatinine phosphokinase (CPK), parathyroid hormone (PTH), eGFR _CysC , eGFR _Cr, , BMD in the lumbar spine (BMD_LS) and femoral neck (BMD_FN) were evaluated with Mann-Whitney U-test. Relationship between BMD for each bone and sex, age, CPK, PTH, Cr/CysC, eGFR _CysC , and being SPS was statistically evaluated with multivariate linear regression analysis. Furtherly, sensitivity and specificity regarding being SPS for T-score < -2.5, that is defined as diagnosis criteria of osteoporosis calculated from BMD, was evaluated with chi square test.

Results: A total of 819 participants with 75 males and 744 females joined. Patient with SPS counted 31 and without SPS counted 782. Underlying diseases are shown in Table 1 . Average age, CysC, Cr, PTH, eGFR _Cr, and eGFR _CysC were 76.5, 1.18, 0.76, 42.1, 66.2 and 59.0, respectively. PTH significantly correlated with CyC (p=0.015), but not correlated with Cr (p=0.079). SPS demonstrated significantly higher ratio for being male (P<1.0x10 ^-10 ), higher age (p=1.07x10 ^-3 ), higher titer of CysC (p=5.5x10 ^-10 ), lower titer of CPK (p=1.5x10 ^-4 ), lower Cr/CysC (P<1.0x10 ^-10 ), lower eGFR _CysC (p=2.8x10 ^-7 ), BMD_LS (P<1.0x10 ^-10 ) and BMD_FN (P<1.0x10 ^-10 ), however no significant difference demonstrated for Cr (2.4x10 ^-1 ), PTH (p=1.7x10 ^-1 ) and Ca (p=6.3x10 ^-1 ). BMD_LS demonstrated significant positive correlation with CPK (p=2.6x10 ^-4 ), and negative correlation with being female (p=4.9x10 ^-7 ), age (p=2.1x10 ^-3 ), PTH (p=2.2x10 ^-2 ), eGFR _CysC (p=2.5x10 ^-9 ) and being SPS (p=4.9x10 ^-3 ), while BMD-FN demonstrated significant positive correlation with Cr/CysC (p=7.3x10 ^-4 ), and negative correlation with being female (p=1.5x10 ^-6 ), age (p=4.9x10 ^-8 ) and being SPS (7.3x10 ^-3 ). Sensitivity and specificity of T-score < -2.5 in the LS regarding SPS was 50.0% and 74.0% (p=6.9x10 ^-3 ), while in the FN 67.9% and 61.7% (p=1.7x10 ^-3 ), respectively.

Conclusion: These results suggested that SPS has serious potential risk of osteoporosis. BMD_LS loss may correlate elevation of PTH due to filtration disorder, however BMD_FN loss is not affected. Split of Cr and CysC is more important.

Disclosure of Interests: None declared