What is the value of measuring renal parenchymal thickness before renal biopsy?

Reduced renal length is widely used to diagnose chronicity in patients with renal impairment. A length of 9 cm or less measured ultrasonographically is considered to indicate irreversible disease. However, some patients with normal renal length have thin parenchyma. The aim of this study was to determine the relationship between ultrasonographically measured parenchymal thickness and renal length and to correlate parenchymal thickness with the histology obtained at renal biopsy. Sixty-four patients, aged 16-74 years, who had had a renal biopsy were evaluated retrospectively. Histology was considered in five categories: I, interstitial nephritis (n = 13); II, glomerulonephritis (28); III, diabetes mellitus/metabolic/other (8); IV, chronic renal disease (CRD) (11); V, hypertension/vascular disease (4). There was a good linear correlation between renal length and renal parenchymal thickness (r = 0.64, P < 0.001). Both were reduced most in patients with CRD. Sixty-four per cent of patients with CRD had renal parenchymal thickness 1.5 cm or less, compared to 38% in group I, 25% in groups II and V, and 7% in group II. Although 11/37 (30%) of patients whose serum creatinine had increased 3 months post-biopsy had parenchymal thickness 1.5 cm or less, so did 6/27 (23%) whose creatinine decreased. Like renal length, parenchymal thickness gives an indication of the chronicity of renal failure. However, some patients with parenchymal thickness 1.5 cm or less still have potential for improvement. This measurement alone should not be used to obviate renal biopsy.