Knowledge of the diameter of a structure or particle is required for stereological calculations. However, there is no consensus on the methodology for its measurement. This study aims to assess the differences between direct and indirect methods of measuring diameter. It is hypothesised that kidneys were removed, fixed, processed, sectioned, and stained. The stained slides were imaged using a digital microscope. The images were processed using the ImageJ software. The diameters of the renal glomeruli and collecting tubules were measured using direct and indirect methods. The measured diameters were analysed using the SPSS software v20. The differences between the measurements were assessed using a Z-test and test of association, and P < 0.05 was considered significant. No significant differences were observed between the diameters of the glomeruli (P = 0.82) and proximal (P = 0.86) and distal (P = 0.55) convoluted tubules as measured via direct and indirect methods. There was a strong positive correlation between the diameters of glomeruli (P = 0.97) and proximal (P = 0.82) and distal (P = 0.93) convoluted tubules measured using the two methods, both of which are convenient, accurate and suitable. The P-values based on these measurements were more than 0.05. Therefore, the study hypothesis was rejected. There was no significant difference between the direct and indirect methods of measuring diameter, and the null hypothesis was rejected; thus, both methods can be applied either independently or jointly.

KEY WORDS: Measurement; Diameter; Direct; Indirect; Glomerulus; Proximal, distal; Convoluted tubules.