Polycystic Kidney Disease (PKD) is a common genetic disorder marked by the growth of numerous fluid-filled sacs, called cysts, within the kidneys. These cysts slowly replace healthy kidney tissue, causing the organs to enlarge and ultimately reducing their ability to filter waste from the blood. This progressive loss of function can lead to chronic kidney disease and, in many cases, kidney failure. Because PKD is inherited, diagnosis involves confirming the presence of cysts, assessing their impact, and determining the genetic type.
Recognizing the Need for Testing and Initial Review
Diagnosis often begins when a person experiences certain symptoms or when family medical history raises a flag. Common signs that prompt a medical visit include high blood pressure, back or side pain, and the presence of blood in the urine (hematuria).
A detailed review of medical and family history is an important initial step, as Autosomal Dominant PKD (ADPKD) accounts for the vast majority of cases and is passed down genetically. The doctor will specifically look for a history of kidney disease, kidney failure, or unexplained strokes in immediate family members. A strong family history of PKD often leads to proactive screening, allowing for earlier management.
Visualizing the Cysts
Imaging is the primary non-invasive method used to confirm a PKD diagnosis by directly visualizing the cysts. Ultrasound is generally the first and most widely used tool, as it is non-invasive, widely available, and effective at detecting fluid-filled cysts. The technique provides real-time images that help assess the number, size, and location of the cysts.
Diagnosis of ADPKD relies on specific, age-based criteria determining the number of cysts required for a positive result. For individuals with a family history between the ages of 15 and 39, at least three total kidney cysts are sufficient for diagnosis. The criteria become more stringent with age: at least two cysts in each kidney are required for those aged 40 to 59, and four or more cysts in each kidney for individuals over 60. This age-adjusted approach is necessary because simple, non-hereditary cysts become common as people get older.
If ultrasound results are inconclusive, especially in younger individuals, advanced imaging may be employed. Computed tomography (CT) or magnetic resonance imaging (MRI) scans can detect smaller cysts than ultrasound and are used to measure the total kidney volume. Measuring this volume is crucial, as increasing kidney size indicates disease progression and helps guide treatment decisions.
Evaluating Organ Function
While imaging confirms the physical presence of the disease, laboratory tests are essential to evaluate the functional impact of the cysts on the kidneys. These tests determine the severity of the disease and provide a baseline for monitoring its progression. Blood tests check the level of creatinine, a waste product that healthy kidneys efficiently remove from the blood.
The concentration of creatinine is used to calculate the estimated Glomerular Filtration Rate (eGFR), which is the best measure of kidney function. The eGFR represents the volume of blood the kidneys can filter per minute; a rate below 60 milliliters per minute suggests chronic kidney disease. A healthy eGFR reading in a person with confirmed cysts indicates the disease is in an early stage.
Urine analysis is also performed to look for abnormalities like protein or blood, which are signs of kidney damage. The presence of protein, specifically albumin, in the urine is an early indicator that the kidney’s filtering units are beginning to fail. These laboratory results, combined with imaging, provide a comprehensive picture of both the physical damage and the functional status.
Genetic Confirmation and Typing
Genetic testing offers definitive confirmation of PKD by identifying the specific gene mutations responsible for the condition. Although imaging is often sufficient for diagnosis, molecular testing is used when imaging results are atypical, when there is no known family history, or when pre-implantation genetic diagnosis is being considered. Identifying the exact gene mutation can also offer prognostic information, as the disease course differs depending on the faulty gene.
The most common form, ADPKD, is primarily linked to mutations in the PKD1 and PKD2 genes. Mutations in PKD1 typically lead to a more rapidly progressive disease form than those in PKD2. Genetic analysis also confirms the diagnosis of the much rarer Autosomal Recessive PKD (ARPKD), which is caused by a mutation in the PKHD1 gene and usually presents in infancy or childhood. Genetic confirmation provides the most precise typing of the disease, but it does not replace the need for regular monitoring of cyst growth and kidney function.