This is a matter of judgment, a decision to be made by the operating physician, balancing benefits of information to be obtained against possibly increased risks of a) a larger bore needle versus b) more sticks with a smaller bore needle.)

        Factors and considerations regarding the amount of tissue needed in various situations is a complex and important topic discussed herein.

        The following photomicrographs will illustrate typical examples of the amount of renal tissue which can be expected to be obtained using needles of various sizes.

        The Franklin-Silverman needle is approximately a 14 gauge.   A typically excellent core obtained by a Silverman needle is shown in the following  picture, at the left, and on the right, at approximately the same magnification, a photomicrograph of a portion of a typical biopsy core obtained with an 18 gauge "automatic" needle.

A comparison of core size with 14- and 18-gauge biopsy needles.

        Other features to keep in mind in comparing the amount of tissue obtainable from each stick of an 18 gauge needle versus a 14 gauge needle are these:

        With a 14-gauge needle the width of the biopsy core is about three or four times the width of a glomerulus, while with an 18-gauge needle the biopsy core is only slightly wider than a single glomerulus.

        This 3-to-1 or 4-to-1 ratio between the diameter of the core of the 14 and 18 gauge needles is further and meaningfully magnified when one considers that the total amount of tissue obtained in a single stick is proportional to the Square of the diameter of the core.   Thus, a biopsy which is two to three times greater diameter,  contains four to nine times more tissue.  

        Since kidney biopsies are ordinarily and routinely serially sectioned, the amount of tissue actually observable and available for evaluation is several fold greater in biopsies obtained by larger gauge needles.  

        Multiple passes by an 18-gauge needle are required to obtained the same sample size which can be obtained by a single pass of a 14 gauge needle.

       The major risk of a kidney biopsy, that of hemorrhage, is generally and perhaps reasonably assumed to be greater with a needle of larger caliber, but I am aware of no evidence which establishes what the increased risk might be.   I strongly suspect that multiple passes with a smaller gauge needle is at least equally likely to increase the probability of excessive bleeding over that associated with the fewer passes ordinarily required using a larger gauge needle.

       That an 18 gauge needle can and often does neatly plug an small muscular artery is well illustrated in the figure immediately above, where a large portion of the wall of an interlobular size artery is clearly shown to have been removed by the biopsy needle.

       An often amazing amount of information is often obtained from a percutaneous kidney biopsy.

       The likelihood that a lesion or lesions will be found is proportional to the amount of tissue obtained. 

       In attempting to estimate the risk-benefit ratio in the performance of the kidney biopsy, the operating physician must bear in mind the possible significance of missing meaningful lesions which may be present.  

      A discussion of factors involved in estimating how much biopsy tissue is needed is included in another section.

      It is my deeply held conviction, that a kidney biopsy is not truly adequately examined, unless tissue is examined thoroughly by an experienced pathologist, using the techniques of light microscopy, immunofluorescence microscopy and electron microscopy.

      The clinical syndromes of medical renal disease are many and complex, and for each one of them, multiple underlying etiologies are possible.  Many patients have more than one pathologic process in the kidney.   Many disorders can ONLY be diagnosed by electron microscopy and/or immunofluorescence.

     It is pertinent to know that a lesion is present, and conversely, that it is not present.

    You will not know, if you do not look, and look carefully.